CaltechAUTHORS: Combined
https://feeds.library.caltech.edu/people/Pellegrino-S/combined.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenWed, 19 Jun 2024 07:50:21 -0700Disordering of InGaAs/GaAs strained quantum well structures induced by rare gas ion implantation
https://resolver.caltech.edu/CaltechAUTHORS:20180605-131242041
Year: 1994
DOI: 10.1117/12.175013
In this work we have investigated the effect of various implantation schemes on In(0.2)GaAs/GaAs/AlGaAs Single Quantum Well, where the implanted species are Argon and Helium, with doses in the range 1E12 to 1E14 at cm^2, at energy spanning 270 - 400 KeV and 30 to 50 KeV for Ar and He, respectively. Repetitive annealing processes were carried out between 735 and 870 degree(s)C and the interdiffusion was deduced by photoluminescence measurements. A maximum of 20 nm shift from He ion implanted Quantum Well with an high degree of reconstruction has been recorded, thus allowing the application of this disordering scheme for the realization of optoelectronic devices.https://resolver.caltech.edu/CaltechAUTHORS:20180605-131242041Design of Al-free and Al-based InGaAs/GaAs strained quantum well 980-nm pump lasers including thermal behavior effects on E/O characteristics
https://resolver.caltech.edu/CaltechAUTHORS:20180614-160352068
Year: 1994
DOI: 10.1117/12.175004
A 2D thermal simulator and a model to evaluate high power lasers characteristics have been developed. With these models it was possible to optimize cavity length of InGaAs/GaAs (Multiple) Quantum Well 980 nm lasers realized both with Al-based and Al-free confining layers. A comprehensive experimental investigation of the influence of cavity length and temperature on the laser emission wavelength has been performed. This allows a fine trimming of the devices to match the Erbium doped fiber absorption bandwidth.https://resolver.caltech.edu/CaltechAUTHORS:20180614-160352068Design of high-power ridge waveguide 980-nm pump lasers
https://resolver.caltech.edu/CaltechAUTHORS:20180605-132224863
Year: 1994
DOI: 10.1117/12.176643
The design of ridge waveguide semiconductor pump lasers poses particular simulation problems, since an accurate modeling of the electric and thermal effects and of the optical guiding capabilities is needed. We developed a model whose self-consistent application allows the evaluation of, among others, the threshold current of the lasing mode and the gain margin of the higher order modes, the P-I characteristic, the power coupled in the fiber, and the far field pattern. Particular attention is paid to the experimental verification of the transverse single mode operation region, and its evolution at high injection levels. The appropriate conditions for operation in the 150 - 200 mW single mode output power range have been found.https://resolver.caltech.edu/CaltechAUTHORS:20180605-132224863Quantum-well-laser mirror degradation investigated by microprobe optical spectroscopy
https://resolver.caltech.edu/CaltechAUTHORS:20180614-161010885
Year: 1995
DOI: 10.1117/12.226195
A study of facet degradation of InGaAs quantum well lasers is reported. We tune up a Raman and photoluminescence micro-probe technique for determining the crystal structure and the temperature profile of the cladding layer, in steps of approximately 1 micrometer, with a temperature resolution better than 1 degree Kelvin. The cladding layer composition and cross- section temperature profile have been monitored during operation. A clear correlation between the facet degradation and the type of protective coating is found.https://resolver.caltech.edu/CaltechAUTHORS:20180614-161010885Cable-Stiffened Pantographic Deployable Structures Part 2: Mesh Reflector
https://resolver.caltech.edu/CaltechAUTHORS:YOUaiaaj97
Year: 1997
The general concept of deployable structures based on pantographs that are deployed and stiffened by means of cables is applied to the design of the support structure for a large mesh reflector. The two main components of this structure are a cable-stiffened pantographic ring that deploys and pretensions a cable network that, in turn, provides a series of stiff, geometrically accurate support points to which a reflective wire mesh or flexible membrane would be connected. The pantographic ring is a highly redundant structure with an internal mechanism that permits synchronous deployment without any strain in the rods. The geometric conditions that have to be satisfied in order for an n-sided ring to fold without any strain are investigated, including the effects of joint size. An experimental model has been designed and tested. In the folded configuration, it has a diameter of 0.6 m and height of 1.2 m; in the deployed configuration, it has a diameter of 3.5 m. Stiffness and deployment tests on this model have shown its behavior to be linear and the maximum shape error to be ±0.3 mm.https://resolver.caltech.edu/CaltechAUTHORS:YOUaiaaj97Modeling and Control of a Flexible Structure Incorporating Inertial Slip-Stick Actuators
https://resolver.caltech.edu/CaltechAUTHORS:DARjgcd99
Year: 1999
Shape and vibration control of a linear flexible structure by means of a new type of inertial slip-stick actuator are investigated. A nonlinear model representing the interaction between the structure and a six-degree-of-freedom Stewart platform system containing six actuators is derived, and closed-loop stability and performance of the controlled systems are investigated. A linearized model is also derived for design purposes. Quasistatic alignment of a payload attached to the platform is solved simply by using a proportional controller based on a linear kinematic model. The stability of this controller is examined using a dynamic model of the complete system and is validated experimentally by introducing random thermal elongations of several structural members. Vibration control is solved using an H∞ loop-shaping controller and, although its performance is found to be less satisfactory than desired, the nonlinear model gives good predictions of the performance and stability of the closed-loop system.https://resolver.caltech.edu/CaltechAUTHORS:DARjgcd99Interaction Between Gravity Compensation Suspension System and Deployable Structure
https://resolver.caltech.edu/CaltechAUTHORS:FISjsr00
Year: 2000
DOI: 10.2514/6.1998-1835
Gravity compensation suspension systems are essential to support space structures during tests on Earth, but also impose constraints on the structures that have the effect of changing their behavior. A computational and experimental study of the interaction of a rigid panel solar array model with a manually adjustable suspension system during quasi-static deployment tests in the 1-g environment of the laboratory is presented. A methodology is established for modeling this interaction, for predicting the effects of suspension system adjustments, and for optimization of the suspension system through these adjustments. Some improvements can be achieved by manual adjustments, but further optimization requires an active system.https://resolver.caltech.edu/CaltechAUTHORS:FISjsr00Deployable Tensegrity Reflectors for Small Satellites
https://resolver.caltech.edu/CaltechAUTHORS:TIBjsr02
Year: 2002
Future small satellite missions require low-cost, precision reflector structures with large aperture that can be packaged in a small envelope. Existing furlable reflectors form a compact package which, although narrow, is too tall for many applications.An alternative approach is proposed, consisting of a deployable "tensegrity" prism forming a ring structure that deploys two identical cable nets (front and rear nets) interconnected by tension ties; the reflecting mesh is attached to the front net. The geometric configuration of the structure has been optimized to reduce the compression in the struts of the tensegrity prism. A small-scale physical model has been constructed to demonstrate the proposed concept. A preliminary design of a 3-m-diam, 10-GHz reflector with a focal-length-to-diameter ratio of 0.4 that can be packaged within an envelope of 0.1 x 0.2 x 0.8 m^3 is presented.https://resolver.caltech.edu/CaltechAUTHORS:TIBjsr02Thin-Shell Deployable Reflectors with Collapsible Stiffeners Part 1: Approach
https://resolver.caltech.edu/CaltechAUTHORS:TANaiaa06
Year: 2006
DOI: 10.2514/1.16320
Thin-shell deployable reflector structures that are folded elastically in a nearly inextensional mode have been recently realized, exploiting the recent availability of high-modulus, ultrathin composite materials. An inherent and significant limitation of this approach is that these structures remain "floppy" in their deployed configuration. This paper presents a general concept for increasing the deployed stiffness of such structures, through the addition of a collapsible edge stiffener around the rim of a reflector dish. Ananalytical expression of the frequency/stiffness related to the softest deformation mode of a thin-shell reflector structure is presented, both with and without the stiffener. During folding, the stiffener collapses elastically, and this behavior is facilitated by the introduction of suitable discontinuities within the stiffener, or between the dish and the stiffener. A detailed study of a range of different options is presented, and one particular scheme is selected and optimized. For a specific example, a stiffness increase by a factor of 31 and a fundamental frequency increase by a factor of 4 are achieved, with a mass increase of only 16%.https://resolver.caltech.edu/CaltechAUTHORS:TANaiaa06Space Frames with Multiple Stable Configurations
https://resolver.caltech.edu/CaltechAUTHORS:SCHIaiaaj07
Year: 2007
DOI: 10.2514/1.16825
This paper is concerned with beamlike spaceframes that include a large number of bistable elements, and exploit the bistability of the elements to obtain structures with multiple stable configurations. By increasing the number of bistable elements, structures with a large number of different configurations can be designed. A particular attraction of this approach is that it produces structures able to maintain their shape without any power being supplied. The first part of this paper focuses on the design and realization of a low-cost snap-through strut, whose two different lengths provide the required bistable feature. A parametric study of the length-change of the strut in relation to the peak force that needs to be applied by the driving actuators is carried out. Bistable struts based on this concept have been made by injection molding nylon. Next, beamlike structures based on different architectures are considered. It is shown that different structural architectures produce structures with workspaces of different size and resolution, when made from an identical number of bistable struts. One particular architecture, with 30 bistable struts and hence over 1 billion different configurations, has been demonstrated.https://resolver.caltech.edu/CaltechAUTHORS:SCHIaiaaj07A bistable structural element
https://resolver.caltech.edu/CaltechAUTHORS:SCHIpime08
Year: 2008
DOI: 10.1243/09544062JMES982
This article presents a novel bistable structural element that has high stiffness in stable configurations, but requires only a small amount of energy to be switched from one configuration to the other. The element is based on a planar linkage of four bars connected by revolute joints,
braced by tape-spring diagonals. A description of the concept is presented, along with a detailed theoretical analysis of its mechanical behaviour. Experimental measurements obtained from a prototype structure are found to be in very good agreement with the predictions from this
analytical model.https://resolver.caltech.edu/CaltechAUTHORS:SCHIpime08Systematically Creased Thin-Film Membrane Structures
https://resolver.caltech.edu/CaltechAUTHORS:PAPjsr08
Year: 2008
DOI: 10.2514/1.18285
This paper presents a study of a square membrane, creased according to the Miura-ori folding pattern. When the membrane is allowed to expand from its packaged configuration, it initially expands elastically under zero corner forces. Starting from this naturally expanded configuration, the paper investigates the stress distribution and the load-displacement relationship when in-plane, diagonal loads are applied at the corners. It is found that out-of-plane bending is the main load-carrying mode and, for stress magnitudes typical of current solar-sail designs, the behavior of the membrane remains linear elastic. A simple analytical model, originally proposed for randomly creased membranes, is shown to predict with good accuracy the load-displacement relationship of the corners. It uses physically based and hence directly measurable membrane parameters.https://resolver.caltech.edu/CaltechAUTHORS:PAPjsr08Simulation of Quasi-Static Folding and Deployment of Ultra-Thin Composite Structures
https://resolver.caltech.edu/CaltechAUTHORS:20200330-081459739
Year: 2008
DOI: 10.2514/6.2008-2053
This paper presents a detailed study of the folding and deployment of a slotted tube hinge made from a two-ply laminate of carbon-fibre reinforced plastic. A physical model of a particular version of this binge has been used to carry out quasi-static deployment tests and this process has been fully captured through a finite element simulation. The first stage in this simulation was to generate the fully folded, strained configuration of the hinge. The second stage in the simulation was to gradually decrease the relative rotation between the ends until it became zero. By analysing the in-plane strains and out-of-plane curvatures in the folded configuration we have confirmed that the particular hinge design that has been studied could be folded without permanent damage.https://resolver.caltech.edu/CaltechAUTHORS:20200330-081459739Computation of Partially Inflated Shapes of Stratospheric Balloon Structures
https://resolver.caltech.edu/CaltechAUTHORS:20200330-082659500
Year: 2008
DOI: 10.2514/6.2008-2133
This paper studies the relationship between height, volume and stress distribution in a superpressure pumpkin balloon with the differential pressure applied to the balloon. Two different approaches are presented. A simple two-dimensional solution based on previous work and a novel, detailed finite element simulation that provides three-dimensional solutions are investigated. It is found that the finite element solution provides a much better agreement with experimental results for the case of a flat facet ULDB balloon. It is also found that a region of tensile hoop stress remains in the crown region of the balloon until the bottom pressure becomes negative. This region prevents the formation of clefts in the balloon and keeps its shape axisymmetric.https://resolver.caltech.edu/CaltechAUTHORS:20200330-082659500Folding Large Antenna Tape Spring
https://resolver.caltech.edu/CaltechAUTHORS:SOYjsr08
Year: 2008
DOI: 10.2514/1.28421
This paper presents a novel concept for a low-mass, 50-m^2-deployable, P-band dual polarization antenna that can measure terrestrial biomass levels from a spacecraft in a low Earth orbit. A monolithic array of feed and radiating patches is bonded to a transversally curved structure consisting of two Kevlar sheets. The first sheet supports the array and the other sheet supports a ground plane. The two sheets are connected by a compliant Kevlar core that allows the whole structure to be folded elastically and to spring back to its original, undamaged shape. Test pieces have been made to demonstrate both the radio frequency and mechanical aspects of the design, particularly the radio frequency performance before and after folding the structure. It is concluded that the proposed design concept has high potential for large, low-frequency antennas for low-cost missions.https://resolver.caltech.edu/CaltechAUTHORS:SOYjsr08Compliant multistable structural elements
https://resolver.caltech.edu/CaltechAUTHORS:SANijss08
Year: 2008
DOI: 10.1016/j.ijsolstr.2008.07.014
Compliant multistable structures are presented which exhibit a large geometric change when actuated between their stable states. It is demonstrated how asymmetric-bistability is achieved through the combination of linear and nonlinear springs. Finite element analytical techniques are provided which enable the design of such structures, and which illustrate how the presence of imperfections can substantially alter their structural performance. A multistable structure is developed which consists of four connected bistable tetrahedral units. The validity of the analytical techniques is confirmed through observation of several physical models.https://resolver.caltech.edu/CaltechAUTHORS:SANijss08Topological optimization of compliant adaptive wing structure
https://resolver.caltech.edu/CaltechAUTHORS:20090506-151236424
Year: 2009
DOI: 10.2514/1.36679
Load-path-based topology optimization is used to synthesize a compliant adaptive aircraft wing leading edge, which deforms in a prescribed way when subject to a single point internal actuation. The load-path-based optimization method requires the specification of a parent lattice. Increasing the complexity of this lattice means the number of parameters required for a complete representation of the structure in the topology optimization becomes prohibitive, although it is desirable to enable a full exploration of the design space. A new method based on graph theory and network analysis is proposed, which enables a substantial reduction in the required number of parameters to represent the parent lattice. The results from this load-path-based approach are compared with those obtained from the better-known density-based topology optimization method.https://resolver.caltech.edu/CaltechAUTHORS:20090506-151236424Multi-objective optimization of free-form grid structures
https://resolver.caltech.edu/CaltechAUTHORS:20091216-121728405
Year: 2010
DOI: 10.1007/s00158-009-0358-4
Computational modeling software facilitates the creation of any surface geometry imaginable, but it is not always obvious how to create an efficient grid shell structure on a complex surface. This paper presents a design tool for synthesis of optimal grid structures, using a Multi-Objective Genetic Algorithm to vary rod directions over the surface in response to two or more load cases. A process of grid homogenization allows the tool to be rapidly applied to any grid structure consisting of a repeating unit cell, including quadrilateral, triangular and double layer grids. Two case studies are presented to illustrate the successful execution of the optimization procedure.https://resolver.caltech.edu/CaltechAUTHORS:20091216-121728405Optimized Designs of Composite Booms with Tape Spring Hinges
https://resolver.caltech.edu/CaltechAUTHORS:20191016-092056718
Year: 2010
DOI: 10.2514/6.2010-2750
This paper presents an optimization study of a lightweight hinge consisting of a thin walled tube made of carbon fiber reinforced plastic with two longitudinal slots. The slot geometry is parameterized in terms of slot length, width and end circle diameter. Previously developed numerical simulation techniques to analyze the folding and deployment of this kind of hinges are used to carry out a series of parametric studies. The maximum strains are estimated by using the mid-surface strain and curvature obtained from a macro model of the structure to a micro model and averaging the strains over a half a tow width in the micro model. A maximum strain failure criterion is used for failure analysis. The optimization study is focused on finding a hinge design that can be folded 180 deg with the shortest possible slot length. Simulations show that the maximum strains can be significantly reduced by allowing the end-cross sections to deform freely. Based on simulations a failure critical model and a failure safe model were selected and experimentally validated. The optimized design is six times stiffer in torsion, twice stiffer axially and stores two and a half times more strain energy than the previously considered design.https://resolver.caltech.edu/CaltechAUTHORS:20191016-092056718Shape Recovery of Viscoelastic Deployable Structures
https://resolver.caltech.edu/CaltechAUTHORS:20191016-090847709
Year: 2010
DOI: 10.2514/6.2010-2606
The paper investigates the shape recovery behavior of a simple beam and a tape spring made of LDPE under prescribed deformation history at room temperature. The linear viscoelastic material properties of LDPE were measured via creep tests. An analysis of a LDPE beam under four-point bending with an imposed history of vertical deflection and reaction force was performed. A theoretical solution was constructed by employing the Alfrey's Correspondence Principle to the Euler-Bernoulli beam equation. The result was validated against a four-point bending experiment and a detailed nonlinear finite element simulation. Excellent agreement was obtained between theory, experiments and numerical simulations. A LDPE tape spring was fabricated and tested to provide an example of a simple deployable structure that recovers its deployed shape through a viscoelastic process for both equal sense and opposite sense folding.https://resolver.caltech.edu/CaltechAUTHORS:20191016-090847709Shape Accuracy of a Joint-Dominated Deployable Mast
https://resolver.caltech.edu/CaltechAUTHORS:20191016-085828334
Year: 2010
DOI: 10.2514/6.2010-2605
This paper presents a study to capture and model friction related changes in the un-loaded configuration of deployable masts with articulated joints. A finite model of a rep-resentative mast structure is described. This model includes a detailed treatment of the latching mechanism. The parameters of the computational model are based on direct mea-surements on components of a physical model. The moment-rotation relationship for a complete single bay of the physical model has been measured and the overall behavior is predicted well by the model, however the model predicts the residual rotation at zero moment to be zero and so it is concluded that a more refined model for the latch will need to be developed.https://resolver.caltech.edu/CaltechAUTHORS:20191016-085828334Wrinkling of Orthotropic Viscoelastic Membranes
https://resolver.caltech.edu/CaltechAUTHORS:20110223-131222888
Year: 2010
This paper presents a simplified simulation technique for orthotropic viscoelastic films.
Wrinkling is detected by a combined stress-strain criterion and an iterative scheme searches
for the wrinkle angle using a pseudo-elastic material stiffness matrix based on a nonlinear
viscoelastic constitutive model. This simplified model has been implemented in
ABAQUS/Explicit and is able to compute the behavior of a membrane structure by superposition
of a small number of response increments. The model has been tested against
a published solution for a time-independent isotropic membrane under simple shear and
also against experimental results on StratoFilm 420 under simple shear.https://resolver.caltech.edu/CaltechAUTHORS:20110223-131222888Maximally stable lobed balloons
https://resolver.caltech.edu/CaltechAUTHORS:20100607-120558442
Year: 2010
DOI: 10.1016/j.ijsolstr.2010.02.013
This paper is concerned with the optimization of the cutting pattern of n-fold symmetric super-pressure balloons made from identical lobes constrained by stiff meridional tendons. It is shown that the critical buckling pressure of such balloons is maximized if the unstressed surface area of the balloon is minimized under a stress constraint. This approach results in fully stressed balloon designs that in some cases have a smaller unstressed surface area than the corresponding axisymmetric surface that is in equilibrium with zero hoop stress. It is shown that, compared to current designs, the buckling pressures can be increased by up to 300% without increasing the maximum stress in the lobe.https://resolver.caltech.edu/CaltechAUTHORS:20100607-120558442Shape correction of thin mirrors in a reconfigurable modular space telescope
https://resolver.caltech.edu/CaltechAUTHORS:20110321-085232350
Year: 2010
DOI: 10.1117/12.861442
In order to facilitate the construction of future large space telescopes, the development of low cost, low mass
mirrors is necessary. However, such mirrors suffer from a lack of structural stability, stiffness, and shape accuracy.
Active materials and actuators can be used to alleviate this deficiency. For observations in the visible wavelengths,
the mirror surface must be controlled to an accuracy on the order of tens of nanometers. This paper presents
an exploration of several mirror design concepts and compares their effectiveness at providing accurate shape
control. The comparison test is the adjustment of a generic mirror from its manufactured spherical shape to the
shape required by various off-axis mirrors in a segmented primary mirror array. A study of thermal effects is
also presented and, from these results, a recommended design is chosen.https://resolver.caltech.edu/CaltechAUTHORS:20110321-085232350A Zero-Stiffness Elastic Shell Structure
https://resolver.caltech.edu/CaltechAUTHORS:20110726-075004792
Year: 2011
DOI: 10.2140/jomms.2011.6.203
A remarkable shell structure is described that, due to a particular combination of geometry and initial stress, has zero stiffness for any finite deformation along a twisting path; the shell is in a neutrally stable state of equilibrium. Initially the shell is straight in a longitudinal direction, but has a constant, nonzero curvature in the transverse direction. If residual stresses are induced in the shell by, for example, plastic deformation, to leave a particular resultant bending moment, then an analytical inextensional model of the shell shows it to have no change in energy along a path of twisted configurations. Real shells become closer to the inextensional idealization as their thickness is decreased; experimental thin-shell models have confirmed the neutrally stable configurations predicted by the inextensional theory. A simple model is described that shows that the resultant bending moment that leads to zero stiffness gives the shell a hidden symmetry, which explains this remarkable property.https://resolver.caltech.edu/CaltechAUTHORS:20110726-075004792Quasi-Static Folding and Deployment of Ultrathin Composite Tape-Spring Hinges
https://resolver.caltech.edu/CaltechAUTHORS:20110322-091936641
Year: 2011
DOI: 10.2514/1.47321
Deployable structures made from ultrathin composite materials can be folded elastically and are able to selfdeploy
by releasing the stored strain energy. This paper presents a detailed study of the folding and deployment of a
tape-spring hinge made from a two-ply plain-weave laminate of carbon-fiber reinforced plastic. Aparticular version
of this hinge was constructed, and its moment-rotation profile during quasi-static deployment was measured. The
present study is the first to incorporate in the simulation an experimentally validated elastic micromechanical model
and to provide quantitative comparisons between the simulations and the measured behavior of an actual hinge.
Folding and deployment simulations of the tape-spring hinge were carried out with the commercial finite element
package Abaqus/Explicit, starting from the as-built unstrained structure. The folding simulation includes the effects
of pinching the hinge in the middle to reduce the peak moment required to fold it. The deployment simulation fully
captures both the steady-state moment part of the deployment and the final snap back to the deployed configuration.
An alternative simulation without pinching the hinge provides an estimate of the maximum moment that could be
carried by the hinge during operation. This is about double the snapback moment.https://resolver.caltech.edu/CaltechAUTHORS:20110322-091936641Viscoelastic effects in tape-springs
https://resolver.caltech.edu/CaltechAUTHORS:20190930-110458819
Year: 2011
DOI: 10.2514/6.2011-2022
Following recent interest in constructing large self-deployable structures made of reinforced polymer materials, this paper presents a detailed study of viscoelastic effects in folding, stowage, and deployment of tape-springs which often act as deployment actuators in space structures. Folding and stowage behavior at different temperatures and rates are studied. It is found that the peak load increases with the folding rate but reduces with temperature. It is also shown that a load reduction of as much as 60% is possible during stowage due to relaxation behavior. Deployment behavior after significant load relaxation demonstrates features distinct from elastic tape-springs. It starts with a short dynamic response, followed by a quasi-static deployment, and ends with a slow creep recovery process. A key feature is that the localized fold stays stationary throughout deployment. Finite element simulations that incorporate an experimentally characterized viscoelastic material model are presented and found to capture the folding and stowage behavior accurately. The general features of deployment response are also predicted, but with larger discrepancy.https://resolver.caltech.edu/CaltechAUTHORS:20190930-110458819Effects of Component Properties on the Accuracy of a Joint-Dominated Deployable Mast
https://resolver.caltech.edu/CaltechAUTHORS:20190930-110458917
Year: 2011
DOI: 10.2514/6.2011-2163
Jointed-dominated deployable masts are used in space applications, including telescopes, where there is a demand for a long, slender structure that can be packed into a conven-tional launch shroud. Depending on the application, there may be stringent demands on the stiffness and shape accuracy of the mast. This paper presents a parametric study of the significance of a number of mast part properties for a precision deployable mast's perfor-mance under quasi-static shear load. The mast's cable preload, latching system behavior, and joint friction are explored as candidates for parts requiring detailed characterization for accurate mast performance prediction.https://resolver.caltech.edu/CaltechAUTHORS:20190930-110458917Design and Validation of Thin-Walled Composite Deployable Booms with Tape-Spring Hinges
https://resolver.caltech.edu/CaltechAUTHORS:20190930-110458726
Year: 2011
DOI: 10.2514/6.2011-2019
This paper presents a 1 m long self-deployable boom that could be folded around a spacecraft. Previously developed simulation techniques are used to analyze this two-hinge boom, made from two-ply plain weave carbon fiber laminate. A stress-resultant based failure criterion is used to study safety of the structure during both stowage and dynamic deployment. A safe design that latches without any overshoot is selected and validated by a dynamic deployment experiment.https://resolver.caltech.edu/CaltechAUTHORS:20190930-110458726Shape Correction of Thin Mirrors
https://resolver.caltech.edu/CaltechAUTHORS:20190930-110457762
Year: 2011
DOI: 10.2514/6.2011-1827
Future large space observatories will require large apertures to provide better resolution and greater light gathering power; thin mirror technologies provide one possible route for addressing this need. This paper presents a study of a 10 m diameter sparse aperture based on a collection of thin, active mirror segments with identical initial shapes. A preliminary design for a 1 m diameter mirror segment is proposed and an investigation into the performance of this design is carried out utilizing finite element modeling tools. The results indicate that it is possible to adapt the generic segment shapes to fit the local mirror shape, and achieve near diffraction-limited performance through the use of lightweight, surface-parallel actuators. These actuators may also be used for thermal compensation. Additionally, a design for a scaled 10 cm diameter prototype mirror to test and validate the envisioned scheme is presented.https://resolver.caltech.edu/CaltechAUTHORS:20190930-110457762Concept and Design of a Multistable Plate Structure
https://resolver.caltech.edu/CaltechAUTHORS:20110921-112358749
Year: 2011
DOI: 10.1115/1.4004459
A concept is presented for a compliant plate structure that deforms elastically into a variety
of cylindrical shapes and is able to maintain such shapes due to the presence of bistable
components within the structure. The whole structure may be fabricated as a
monolithic entity using low-cost manufacturing techniques such as injection molding.
The key steps in the analysis of this novel concept are presented, and a functional model
is designed and constructed to demonstrate the concept and validate the analysis.https://resolver.caltech.edu/CaltechAUTHORS:20110921-112358749DEORBITSAIL: De-orbiting of satellites using solar sails
https://resolver.caltech.edu/CaltechAUTHORS:20191004-152131563
Year: 2011
DOI: 10.1109/icspt.2011.6064667
Historical practice of abandoning satellites at the end of their lifetime has left 8,500 tonnes of space waste in Low Earth Orbit. In the future, this practice must change. DEORBIT SAIL proposes an innovative system, allowing the safe de-orbiting of spacecraft at the end of their lifetime. Increasingly, space debris poses a risk for spacecraft. Hundreds of old satellites and thousands of pieces of space junk orbit Earth. Such debris collide, which in turn increases the amount of debris, as pieces of old satellites break of when hit by pieces of other retired spacecraft. Indeed, without a change of practice and the establishment of effective systems for safe de-orbiting of spacecraft at the end of their lifetime, it is estimated that the number of debris particles will grow with a growth rate in the order of 5 percent per year - a percentage which would raise over time as the number of possible collisions increase. The DEORBITSAIL project addresses this challenge, as it is set to develop a novel low cost low risk de-orbiting device for smaller spacecraft with a mass less than 500 kg that circulate Earth in Low Earth Orbit less than 900 km above us. DEORBITSAIL proposes to develop a 25 square metre Solar Sail, which would weight no more than 3 kg. Upon the end of its lifetime, the retired spacecraft would deploy this sail. Within 25 years, drag will drive the spacecraft downwards, taking the spacecraft home into Earth's atmosphere, where it would burn off safely. The 25 year de-orbiting period adheres to established recommendations by the European Space Agency (ESA), and deployed on all new small size spacecraft. DEORBITSAIL has the potential to reduce future debris by 70 percent. DEORBITSAIL is a fully funded space mission, sponsored by the EU FP7 program.https://resolver.caltech.edu/CaltechAUTHORS:20191004-152131563Constitutive modeling of fiber composites with a soft hyperelastic matrix
https://resolver.caltech.edu/CaltechAUTHORS:20120321-092722311
Year: 2012
DOI: 10.1016/j.ijsolstr.2011.11.006
This paper presents an experimental and numerical study of unidirectional carbon fiber composites with a silicone matrix, loaded transversally to the fibers. The experiments show nonlinear behavior with significant strain softening under cyclic loading. The numerical study uses a plane-strain finite element continuum model of the composite material in which the fiber distribution is based on experimental observations and cohesive elements allow debonding to take place at the fiber/matrix interfaces. It is found that accurate estimates of the initial tangent stiffness measured in the experiments can be obtained without allowing for debonding, but this feature has to be included to capture the non-linear and strain-softening behavior.https://resolver.caltech.edu/CaltechAUTHORS:20120321-092722311Folding of fiber composites with a hyperelastic matrix
https://resolver.caltech.edu/CaltechAUTHORS:20120321-093716989
Year: 2012
DOI: 10.1016/j.ijsolstr.2011.09.010
This paper presents an experimental and numerical study of the folding behavior of thin composite materials consisting of carbon fibers embedded in a silicone matrix. The soft matrix allows the fibers to microbuckle without breaking and this acts as a stress relief mechanism during folding, which allows the material to reach very high curvatures. The experiments show a highly non-linear moment vs. curvature relationship, as well as strain softening under cyclic loading. A finite element model has been created to study the micromechanics of the problem. The fibers are modeled as linear-elastic solid elements distributed in a hyperelastic matrix according to a random arrangement based on experimental observations. The simulations obtained from this model capture the detailed micromechanics of the problem and the experimentally observed non-linear response. The proposed model is in good quantitative agreement with the experimental results for the case of lower fiber volume fractions but in the case of higher volume fractions the predicted response is overly stiff.https://resolver.caltech.edu/CaltechAUTHORS:20120321-093716989Thin-Shell Deployable Reflectors with Collapsible Stiffeners: Experiments and Simulations
https://resolver.caltech.edu/CaltechAUTHORS:20120416-095858746
Year: 2012
DOI: 10.2514/1.J051254
This paper presents an experimental and computational study of four deployable reflectors with collapsible edge
stiffeners, to verify the differences in behavior that had been predicted in a previous theoretical study. The
experimental models have different geometric configurations and are made of two different plastics. Both folding
experiments and vibration tests in the fully deployed configuration are carried out on each model, and it is shown that
good correlation with finite element simulations can be achieved if detailed effects such as material nonlinearity,
geometric imperfections, air, and gravity effects are included in the computer models.https://resolver.caltech.edu/CaltechAUTHORS:20120416-095858746Wrinkling of Orthotropic Viscoelastic Membranes
https://resolver.caltech.edu/CaltechAUTHORS:20120402-094931274
Year: 2012
DOI: 10.2514/1.J051255
This paper presents a simplified simulation technique for orthotropic viscoelastic membranes. Wrinkling is
detected by a combined stress–strain criterion and iterative scheme searches for the wrinkle angle using a
pseudoelastic material stiffness matrix based on a nonlinear viscoelastic constitutive model. This simplified model has
been implemented in ABAQUS/Explicit and is able to compute the behavior of a membrane structure by
superposition of a small number of response increments. The model has been tested against a published solution for a
time-independent isotropic membrane under simple shear and against experimental results on Stratofilm 420 under
simple shear.https://resolver.caltech.edu/CaltechAUTHORS:20120402-094931274Thin deformable mirrors for a reconfigurable space telescope
https://resolver.caltech.edu/CaltechAUTHORS:20160303-153240359
Year: 2012
DOI: 10.2514/6.2012-1668
As part of a small satellite technology demonstration that will utilize autonomous assembly, reconfiguration, and docking technology to form the primary mirror for the mission's telescope payload, the mirror segments are required to modify and control their shape, in order to allow for imaging in different configurations. This paper focuses on the development of 10 cm diameter active lightweight mirrors. The current mirror design, control scheme, and fabrication methods are described, as well as experimental results on initial samples. The data demonstrates that the mirrors are capable of at least 100 microns of displacement during operation, and that fabrication on polished molds can result in high quality reflective surfaces.https://resolver.caltech.edu/CaltechAUTHORS:20160303-153240359Design of Lightweight Structural Components for Direct Digital Manufacturing
https://resolver.caltech.edu/CaltechAUTHORS:20190826-092412796
Year: 2012
DOI: 10.2514/6.2012-1807
The rapid growth in direct digital manufacturing technologies has opened the challenge of designing optimal micro-structures for high-performance components. Current topology optimization techniques do not work well for this type of problems and hence in this paper we propose a technique based on an implicit representation of the structural topology. The detailed microstructure is defined by a continuous variable, the size distribution field, defined over the design domain by chosen shape functions. We can optimize the structural topology by optimizing only the weights of the size distribution field and, for any given size distribution, we use standard meshing software to determine the actual detailed micro-structure. We have implemented the optimization loop using commercial CAD and FEA software, running under a genetic algorithm in MATLAB. Application this novel technique to the design of a sandwich beam has produced designs that are superior to any standard solid beam or even optimized truss structure.https://resolver.caltech.edu/CaltechAUTHORS:20190826-092412796Micromechanical modeling of deployment and shape recovery of thin-walled viscoelastic composite space structures
https://resolver.caltech.edu/CaltechAUTHORS:20190828-102318423
Year: 2012
DOI: 10.2514/6.2012-1910
The first part of the paper presents an experimental study of the deployment and shape recovery of composite tape-springs after stowage at an elevated temperature. It is found that tape-springs deploy quickly and with a slight overshoot, but complete recovery takes place asymptotically over time. Stowage has the effect of slowing down both the shortterm deployment and long-term shape recovery. The second part of the paper presents a micromechanical finite element homogenization scheme to determine the effective viscoelastic properties of woven composite laminas. This solution scheme is employed in numerical simulations of deployment and shape recovery of composite tape-springs. The proposed micromechanical model predicts both the short-term deployment and long-term shape recovery response with close agreement to the experimental measurements.https://resolver.caltech.edu/CaltechAUTHORS:20190828-102318423Characterization of a high strain composite material
https://resolver.caltech.edu/CaltechAUTHORS:20190828-102318305
Year: 2012
DOI: 10.2514/6.2012-1909
L'Garde has designed and developed a high-strain composite material consisting of car- bon FIbers embedded in a silicone matrix. The behavior of this material is significantly different from standard composites and the paper presents special test methods to measure the properties of this material. It is found that rule of mixtures estimates are quite accurate for the longitudinal moduli in tension and bending, but less accurate for compression. The Poisson's ratio prediction is also not accurate. Regarding the strength of the composite, it is found that conservative predictions of tensile and compressive strengths can be obtained respectively from the Weibull distribution of the strength of a single fiber combined with a simple bundle theory, and the elastic fiber microbuckling stress.https://resolver.caltech.edu/CaltechAUTHORS:20190828-102318305Structural Architectures for a Deployable Wideband UHF Antenna
https://resolver.caltech.edu/CaltechAUTHORS:20190826-092412894
Year: 2012
DOI: 10.2514/6.2012-1836
This paper explores concepts for a wideband deployable antenna suitable for small satellites. The general approach taken was to closely couple antenna theory and structural mechanics, to produce a deployable antenna that is considered efficient in both fields. Approaches that can be deployed using stored elastic strain energy have been favored over those that require powered actuators or environmental effects to enforce deployment. Two types of concepts were developed: thin shell structure and pantograph. These concepts cover four antenna topologies: crossed log periodic, conical log spiral, helical and quadrifilar helix. Of these, the conical log spiral antenna and the accompanying deployment concepts are determined to be the most promising approaches that warrant further study.https://resolver.caltech.edu/CaltechAUTHORS:20190826-092412894Satellite Hardware: Stow-and-Go for Space Travel
https://resolver.caltech.edu/CaltechAUTHORS:20120604-143122907
Year: 2012
Man-made satellites have to fit a lot into a compact package. Protected inside a rocket while blasted through the atmosphere, a satellite is launched into Earth orbit, or beyond, to continue its unmanned mission alone. It uses gyroscopes, altitude thrusters, and magnets to regulate sun exposure and stay pointed in the right direction. Once stable, the satellite depends on solar panels to recharge its internal batteries, mirrors, and lenses for data capture, and antennas for communication back to Earth. Whether it is a bread-loaf-sized nano, or the school bus sized Hubble Telescope, every satellite is susceptible to static electricity buildup from solar wind, the very cold temperatures the Earth's shadow (or deep space), and tiny asteroids along the route.https://resolver.caltech.edu/CaltechAUTHORS:20120604-143122907A Technique to Predict Clefting of Lobed Super-Pressure Balloons
https://resolver.caltech.edu/CaltechAUTHORS:20190918-090257435
Year: 2012
DOI: 10.2514/6.2011-6830
Lobed super-pressure balloons have shown a tendency to deploy into unexpected asymmetric shapes, hence their design has to strike a balance between the lowest stresses achieved by increasing lobing and the risk of incomplete deployment. This paper proposes a computational clefting test that can be applied to any given balloon design. The test consists in setting up the balloon in its symmetrically inflated configuration, then breaking the symmetry of this shape by artificially introducing a clefting imperfection, and finally determining the equilibrium shape of the balloon. Wrinkling of the balloon film and frictionless contact are included in the computation. The clefting test is applied successfully to three 27 m diameter super-pressure balloons that have been tested indoors by NASA, of which one had remained clefted when it was inflated and the other two had deployed completely.https://resolver.caltech.edu/CaltechAUTHORS:20190918-090257435Large Strain Viscoelastic Model for Balloon Film
https://resolver.caltech.edu/CaltechAUTHORS:20190918-093409950
Year: 2012
DOI: 10.2514/6.2011-6939
This paper presents a constitutive model capable of predicting the anisotropic viscoelastic behavior of balloon film subject to large strains and cyclic loading. The model is based on the free volume theory of nonlinear viscoelasticity enhanced with a switching rule for treating loading and unloading differently. The model has been implemented in the finite element analysis program Abaqus/Standard and the results have been compared with experiments on the balloon film StratoFilm 420 under biaxial tension and shear.https://resolver.caltech.edu/CaltechAUTHORS:20190918-093409950Folding of Thin Composite Structures with a Soft Matrix
https://resolver.caltech.edu/CaltechAUTHORS:20191218-112129907
Year: 2012
DOI: 10.2514/6.2009-2633
The paper presents detailed micromechanical finite element simulations of composite materials with soft materials undergoing large macroscopic bending deformation. The simulations allow the study of fibre microbuckling under bending, including the kinematics of the fibres, as well as the strains in the matrix. These simulations lead to a simple analytical model that allows a quite accurate estimation of the buckling wavelength. It also provides the moment-curvature relationship. Finally, the model is also able to predict the maximum strain in the fibres for a given curvature.https://resolver.caltech.edu/CaltechAUTHORS:20191218-112129907Deployment Dynamics of Composite Booms with Integral Slotted Hinges
https://resolver.caltech.edu/CaltechAUTHORS:20191218-095027064
Year: 2012
DOI: 10.2514/6.2009-2631
This paper considers a lightweight boom with an integral hinge consisting of a thin-walled tube made of carbon fibre reinforced plastic with two longitudinal slots. The dynamic deployment of this boom is studied both experimentally and by means of detailed finite-element simulations. The deployment of the boom can be divided into three phases: deployment; incomplete latching, buckling of the tape springs and large rotation of the boom; and vibration of the boom in latched configuration. The simulations show that the most critical phase is the second one, as the highest strains in both the fibres and the matrix occur at this stage. Through the simulations it is found that the deployment of the particular boom design studied in this paper is quite sensitive to the details of the gravity offload system.https://resolver.caltech.edu/CaltechAUTHORS:20191218-095027064Space-quality data from balloon-borne telescopes: the High Altitude Lensing Observatory (HALO)
https://resolver.caltech.edu/CaltechAUTHORS:20121212-100123634
Year: 2012
DOI: 10.1016/j.astropartphys.2012.05.015
We present a method for attaining sub-arcsecond pointing stability during sub-orbital balloon flights, as
designed for in the High Altitude Lensing Observatory (HALO) concept. The pointing method presented here
has the potential to perform near-space quality optical astronomical imaging at ~1–2% of the cost of
space-based missions. We also discuss an architecture that can achieve sufficient thermo-mechanical stability
to match the pointing stability. This concept is motivated by advances in the development and testing
of Ultra Long Duration Balloon (ULDB) flights which promise to allow observation campaigns lasting
more than three months. The design incorporates a multi-stage pointing architecture comprising: a gondola
coarse azimuth control system, a multi-axis nested gimbal frame structure with arcsecond stability,
a telescope de-rotator to eliminate field rotation, and a fine guidance stage consisting of both a telescope
mounted angular rate sensor and guide CCDs in the focal plane to drive a Fast-Steering Mirror. We discuss
the results of pointing tests together with a preliminary thermo-mechanical analysis required for subarcsecond
pointing at high altitude. Possible future applications in the areas of wide-field surveys and
exoplanet searches are also discussed.https://resolver.caltech.edu/CaltechAUTHORS:20121212-100123634Failure of Carbon Fibers at a Crease in a Fiber-Reinforced Silicone Sheet
https://resolver.caltech.edu/CaltechAUTHORS:20130204-114025514
Year: 2013
DOI: 10.1115/1.4007082
Thin sheets of unidirectional carbon fibers embedded in a silicone matrix can be folded to very high curvatures, as elastic microbuckles with a half-wavelength on the order of 1 mm decrease the maximum strain in the fibers near the compression surface. This paper shows that probabilistic failure models derived from tension tests on individual fibers can be used to predict accurately the value of the outer surface curvature of the sheet, at which a small percentage of fibers break when a crease is formed in the sheet. The most accurate results are obtained by using a strain-based Weibull distribution of the failure probability in tension.https://resolver.caltech.edu/CaltechAUTHORS:20130204-114025514Deployable Helical Antennas for CubeSats
https://resolver.caltech.edu/CaltechAUTHORS:20131120-152814552
Year: 2013
DOI: 10.2514/6.2013-1671
This paper explores the behavior of a self-deploying helical pantograph antenna for CubeSats. The helical pantograph concept is described along with concepts for attachment to the satellite bus. Finite element folding simulations of a pantograph consisting of eight helices are presented and compared to compaction force experiments done on a prototype antenna. Reflection coefficient test are also presented, demonstrating the operating frequency range of the prototype antenna. The helical pantograph is shown to be a promising alternative to current small satellite antenna solutions.https://resolver.caltech.edu/CaltechAUTHORS:20131120-152814552Design and testing of imperfection-insensitive monocoque cylindrical shells
https://resolver.caltech.edu/CaltechAUTHORS:20190826-092412987
Year: 2013
DOI: 10.2514/6.2013-1768
The high efficiency of monocoque cylindrical shells in carrying axial loads is curtailed by their extreme sensitivity to imperfections. For practical applications, this issue has been alleviated by introducing closely stiffened shells which, however, require expensive manufacturing. Here we present an alternative approach that provides a fundamentally different solution. We design symmetry-breaking wavy cylindrical shells that avoid imperfection sensitivity. Their cross-section is formulated by NURBS interpolation on control points whose positions are optimized by evolutionary algorithms. We have applied our approach to both isotropic and orthotropic shells and have also constructed optimized composite wavy shells and measured their imperfections and experimental buckling loads. Through these experiments we have confirmed that optimally designed wavy shells are imperfection-insensitive. We have studied the mass efficiency of these new shells and found them to be more efficient than even a perfect circular cylindrical shell and most stiffened cylindrical shells.https://resolver.caltech.edu/CaltechAUTHORS:20190826-092412987Origami Sunshield Concepts for Space Telescopes
https://resolver.caltech.edu/CaltechAUTHORS:20190816-144340816
Year: 2013
DOI: 10.2514/6.2013-1594
This paper presents two origami inspired concepts for sunshields for a deployable X-ray space telescope. Analytical models of the fold layout and sunshield deployment have been derived, and these models have been used to match the sunshield design to a set of geometric constraints. To validate the design, a proof-of-concept physical model of the optimized analytical design was constructed at 1:10 scale.https://resolver.caltech.edu/CaltechAUTHORS:20190816-144340816Ultra-Thin Highly Deformable Composite Mirrors
https://resolver.caltech.edu/CaltechAUTHORS:20190816-144340709
Year: 2013
DOI: 10.2514/6.2013-1523
Optical quality mirrors are heavy, expensive and difficult to manufacture. This paper presents a novel mirror concept based on an active laminate consisting of an ultra-thin carbon-fiber shell bonded to a piezo-ceramic active layer coated with patterned electrodes. Mirrors based on this concept are less than 1 mm thick and hence are very lightweight and flexible. They also have a large dynamic range of actuation that allows them to take up a wide range of deformed configurations. This concept is compatible with relatively high-volume manufacturing processes and can potentially achieve a significant reduction in cost in comparison to currently available active mirrors. It is also suitable for applications ranging from concentrators for solar power generation to primary mirrors for optical telescopes. The paper presents an overview of the mirror components as well as a simple design relationship for sizing the active layer. The expected performance of a preliminary design for a 1 m diameter mirror with a radius of curvature of 15 m is computed numerically, showing that a set of 96 actuators can remove an edge-to-edge manufacturing-induced cylindrical curvature of 5 mm to an RMS accuracy of 50 μm. The prescription of the mirror can also be adjusted to a radius of curvature of 11 m with an accuracy of 160 μm. The development and characterization of a proof-of-concept prototype mirror is also presented.https://resolver.caltech.edu/CaltechAUTHORS:20190816-144340709Failure criterion for two-ply plain-weave CFRP laminates
https://resolver.caltech.edu/CaltechAUTHORS:20130625-091951266
Year: 2013
DOI: 10.1177/0021998312447208
We present an experimentally based failure criterion for symmetric two-ply plain-weave laminates of carbon fiber reinforced plastic. The criterion is formulated in terms of six force and moment stress resultants and consists of a set of three inequalities, related to in-plane, bending, and combined in-plane and bending types of failure. All failure parameters in the criterion are measured directly from five sets of tests. The new criterion is validated against an extensive data set of failure test results that use novel sample configurations to impose different combinations of stress resultants. It is found that the proposed criterion is safe for all test conditions and yet avoids excessive conservatism.https://resolver.caltech.edu/CaltechAUTHORS:20130625-091951266Parylene origami structure for intraocular implantation
https://resolver.caltech.edu/CaltechAUTHORS:20140520-140334969
Year: 2013
DOI: 10.1109/Transducers.2013.6627077
This paper presents the use of origami technique to construct a 3D spherical structure from a 2D parylene-C (PA-C) film with designed folding crease patterns. This origami technique is developed or intended for intraocular epiretinal implant application, which requires a "curved" electrode array to match the curvature of the macula. The folding method and process are described here using silicone oil as a temporary glue to hold the folded structures through meniscus force. The temporary origami is then thermally set into permanent 3D shapes at 100 °C for 30 minutes in vacuum utilizing parylene-C's viscoelastic properties. The reported origami technique enables the possibility of first making an extended device in 2D format and, after a possible minimal surgical cut and insertion, then folding it into a 3D device inside the eye for necessary geometric matching with host tissues.https://resolver.caltech.edu/CaltechAUTHORS:20140520-140334969Folding, Stowage, and Deployment of Viscoelastic Tape Springs
https://resolver.caltech.edu/CaltechAUTHORS:20130829-140823015
Year: 2013
DOI: 10.2514/1.J052269
This paper presents an experimental and numerical study of the folding, stowage, and deployment behavior of
viscoelastic tape springs. Experiments show that during folding the relationship between load and displacement is
nonlinear and varies with rate and temperature. In particular, the limit and propagation loads increase with the
folding rate but decrease with temperature. During stowage, relaxation behavior leads to a reduction in internal
forces that significantly impacts the subsequent deployment dynamics. The deployment behavior starts with a short,
dynamic transient that is followed by a steady deployment and ends with a slow creep recovery. Unlike elastic tape
springs, localized folds in viscoelastic tape springs do not move during deployment. Finite-element simulations based
on a linear viscoelastic constitutive model with an experimentally determined relaxation modulus are shown to
accurately reproduce the experimentally observed behavior, and to capture the effects of geometric nonlinearity, time
and temperature dependence.https://resolver.caltech.edu/CaltechAUTHORS:20130829-140823015Effects of Viscoelasticity on the Deployment of Bistable Tape Springs
https://resolver.caltech.edu/CaltechAUTHORS:20191002-151926429
Year: 2013
The effects of stowage on the deployment of composite bistable tape springs are studied. A viscoelastic analytical model is used to predict the relaxation and stability of the structure in its coiled state. The time-dependent stability analysis reveals that the structure remains bistable throughout the relaxation process. A dynamic model is then applied to predict the deployment of the structure once it is released. Experimental deployment results match the deployment predictions within 3% for the case where no stowage is applied. It is shown that stowage causes an increase in the deployment time; in this case, experimental deployment times overshoot those predicted by the model. Secondary effects are observed at high stowage temperatures, which are not predicted by the analytical model. These effects include an abrupt change in the
deployment dynamics and a large increase in the deployment time (deployment latency). At higher temperatures still, i.e. for stowage at 100°C, the structure fails to deploy and becomes stable at all extended lengths.https://resolver.caltech.edu/CaltechAUTHORS:20191002-151926429Manufacture of Arbitrary Cross-Section Composite Honeycomb Cores Based on Origami Techniques
https://resolver.caltech.edu/CaltechAUTHORS:20130919-145814478
Year: 2013
DOI: 10.1115/DETC2013-12743
In recent years, the use of composite materials has drastically increased in the construction of aerospace components. In the case of sandwich panels, they have been extensively used as face sheets with aluminum honeycomb cores. Currently, space structures are increasing in size and require greater degrees of accuracy; hence, the use of composites as a core material is a natural progression. However, these composite core materials are not regularly used in sandwich construction. Compared to standard aluminum honeycombs, their manufacturing costs are very high and they have limited applications. Another problem is difficulty of machining. In the manufacture of complex-shaped parts, the cores must have some degree of curvature. For aluminum honeycombs, this can be done using a contour cutter, a 3-D tracer, and numerically controlled machines. However, burrs and buckling of cell walls present a difficult problem for surface accuracy. It is clear that the machining of composite cores requires more expensive and sophisticated systems. This study illustrates a new strategy to fabricate arbitrary cross-section honeycomb cores with applications of advanced composite materials. These types of honeycombs are usually manufactured from normal flat honeycombs by curving or carving, but the proposed method enables us to construct objective shaped honeycombs directly. The basic idea originates from the fold-made paper honeycombs proposed by authors, in which they attempted to apply origami and kirigami techniques to the creation of sandwich structures. Origami is the traditional Japanese art of paper folding. Kirigami is a variation of origami. We first introduce the concept of the origami honeycomb, which is made from single flat sheets with periodical slits resembling origami. In previous studies, honeycombs having various shapes were made using this method, and were realized by only changing folding line diagrams (FLDs). In this study, these 3D origami honeycombs are generalized by numerical parameters and fabricated using a newly proposed FLD design method, which enables us to draw the FLD of arbitrary cross-section honeycombs. Next, we describe a method of applying this technique to advanced composite materials. For partially soft composites, folding lines are materialized by silicon rubber hinges on carbon fiber reinforced plastic. Complex FLD patterns are then printed using masks on carbon fabrics. Finally, these foldable composites that are cured in corrugated shapes in autoclaves are folded into honeycomb shapes, and some typical samples are shown with their FLDs.https://resolver.caltech.edu/CaltechAUTHORS:20130919-145814478Ultralightweight deformable mirrors
https://resolver.caltech.edu/CaltechAUTHORS:20130822-142341866
Year: 2013
DOI: 10.1364/AO.52.005327
This paper presents a concept for ultralightweight deformable mirrors, based on a thin substrate of optical surface quality, coated with continuous active layers that provide separate modes of actuation at different length scales. This concept eliminates any kind of stiff backing structure for the mirror surface and exploits microfabrication technologies to provide tight integration of the active materials into the mirror structure, to avoid actuator print-through effects. Proof-of-concept, 10 cm diameter mirrors with an areal density of 0.6 kg/m^2 have been designed, built, and tested to measure their shape-correction performance and verify the finite-element models used for design. The low-cost manufacturing scheme involves low-temperature processing steps (below 140°C) to minimize residual stresses, does not require precision photolithography, and is therefore scalable to larger diameters depending on application requirements.https://resolver.caltech.edu/CaltechAUTHORS:20130822-142341866Failure of Polyethylene Thin Film Membrane Structures
https://resolver.caltech.edu/CaltechAUTHORS:20190821-102001622
Year: 2013
The failure of balloons made of Linear Low Density PolyEthylene (LLDPE) is investigated. The chosen film is 38 μm thick StratoFilm 420, currently used for the NASA Super-Pressure balloons [1]. The visco-elastic behaviour of the film has been extensively studied and is already accounted for in the balloon design [2, 3, 5]. The next step in the development of accurate predictive tools for super-pressure balloons requires models that capture the transition from visco-elastic and visco-plastic behaviour to fracture. It is shown that realistic estimates of failure of LLDPE membrane structures can be obtained from visco-elastic simulations based on the non-linear visco-elastic model of the balloon film proposed by Kwok [5], supplemented with a fracture resistance criterion derived from the experimentally-based J-integral.https://resolver.caltech.edu/CaltechAUTHORS:20190821-102001622UHF deployable antenna structures for CubeSats
https://resolver.caltech.edu/CaltechAUTHORS:20190814-154556302
Year: 2014
DOI: 10.1109/usnc-ursi-nrsm.2014.6928057
Antenna design for small satellites such as CubeSats constitute a challenge for designers especially at UHF frequencies. The small size of the CubeSat (10 cm x 10 cm x 10 cm) imposes several constraints on the antenna design. Extreme packaging ratios and advanced deployment mechanisms have to be employed to cater for UHF antennas on a CubeSat platform.https://resolver.caltech.edu/CaltechAUTHORS:20190814-154556302Multi-layered membrane structures with curved creases for smooth packaging and deployment
https://resolver.caltech.edu/CaltechAUTHORS:20140324-181344254
Year: 2014
DOI: 10.2514/6.2014-1037
We present a design for a deployable multi-layered membrane structure that uses a curved crease pattern
to enable smooth wrapping around a spool. The crease pattern is parameterized to enable a variety of designs,
and a specific implementation was selected based on an existing patch antenna array design. We constructed a
prototype structure based on this geometry, and conducted deployment tests to measure the deployment force
profile required to unfold the structure and to unwrap it from a spool. We find that the deployment force
for unwrapping is significantly higher than for unfolding. These force profiles are repeatable over multiple
deployments and the global trends do not depend on deployment rates over the range tested, between 1 and
8 mm/s. However, the local dynamic behavior can depend on deployment rate.https://resolver.caltech.edu/CaltechAUTHORS:20140324-181344254Self-Supporting Membrane Structures with Curved Creases for Smooth Packaging and Deployment
https://resolver.caltech.edu/CaltechAUTHORS:20190820-140510587
Year: 2014
DOI: 10.2514/6.2014-1037
We present a design for a deployable multi-layered membrane structure that uses a curved crease pattern to enable smooth wrapping around a spool. The crease pattern is parameterized to enable a variety of designs, and a specific implementation was selected based on an existing patch antenna array design. We constructed a prototype structure based on this geometry, and conducted deployment tests to measure the deployment force profile required to unfold the structure and to unwrap it from a spool. We find that the deployment force for unwrapping is significantly higher than for unfolding. These force profiles are repeatable over multiple deployments and the global trends do not depend on deployment rates over the range tested, between 1 and 8 mm/s. However, the local dynamic behavior can depend on deployment rate.https://resolver.caltech.edu/CaltechAUTHORS:20190820-140510587Deployment mechanics of highly compacted thin membrane structures
https://resolver.caltech.edu/CaltechAUTHORS:20190820-141521974
Year: 2014
DOI: 10.2514/6.2014-1038
We studied the effects of membrane thickness and crease density on the forces required to unfold creased membrane structures. 26 cm-diameter models were made using two different thicknesses (7.5 μm and 25 μm) of polyimide film, and wrapped around a 4 cm-diameter hub using two different crease densities. They were deployed quasi-statically, and the deployment forces were measured. Two regimes were observed: an initial phase (up to about 85% deployed) of low and variable stiffness, and a second phase (above 85% deployed) of high stiffness. The thinner membrane models required higher deployment forces than the thicker membrane models during the initial phase.https://resolver.caltech.edu/CaltechAUTHORS:20190820-141521974A Fractionated Space Weather Base at L_5 using CubeSats and Solar Sails
https://resolver.caltech.edu/CaltechAUTHORS:20170622-081730492
Year: 2014
DOI: 10.1007/978-3-642-34907-2_19
The Sun–Earth L_5 Lagrange point is an ideal location for an operational space weather forecasting mission to provide early warning of Earth-directed solar storms (coronal mass ejections, shocks and associated solar energetic particles). Such storms can cause damage to power grids, spacecraft, communications systems and astronauts, but these effects can be mitigated if early warning is received. Space weather missions at L5 have been proposed using conventional spacecraft and chemical propulsion at costs of hundreds of millions of dollars. Here we describe a mission concept that could accomplish many of the goals at a much lower cost by dividing the payload among a cluster of interplanetary CubeSats that reach orbits around L5 using solar sails.https://resolver.caltech.edu/CaltechAUTHORS:20170622-081730492Deployment Dynamics of Ultrathin Composite Booms with Tape-Spring Hinges
https://resolver.caltech.edu/CaltechAUTHORS:20140501-090732942
Year: 2014
DOI: 10.2514/1.A32401
An experimental and numerical study of the dynamic deployment of stored strain energy deployable booms with tape-spring hinges made of woven carbon fiber composite is presented. The deployment consists of three phases: deployment, one or more attempts to latch, and a small amplitude vibration. Twelve nominally identical deployment experiments show that the deployment and vibration phases are repeatable, whereas considerable scatter is observed during latching. A high-fidelity finite element shell model of the complete boom is used to carry out complete dynamic simulations with the Abaqus/Explicit finite element software. These analyses provide detailed time histories of deformation and stress distribution. By varying the end conditions at the root of the boom and the viscous pressure loading on the surface of the hinge region, the analyses provide 1) an envelope of responses that bound the complete set of experimental observations and 2) responses that closely approximate actual experiments. The presented approach is fully general and can provide high-fidelity simulations for any kind of stored-energy deployable structure.https://resolver.caltech.edu/CaltechAUTHORS:20140501-090732942Trajectory Planning for CubeSat Short-Time-Scale Proximity Operations
https://resolver.caltech.edu/CaltechAUTHORS:20140626-094453645
Year: 2014
DOI: 10.2514/1.60289
This paper considers motion planning for small satellites such as CubeSats performing proximity operations in a several meters range of a target object. The main goal is to develop a principled methodology for handling the coupled effects of orbital dynamics, rotational and translational rigid-body dynamics, underactuation and control bounds, and obstacle avoidance constraints. The proposed approach is based on constructing a reduced-order parameterization of the dynamics through dynamics inversion and differential flatness, and on efficient global optimization over a finite-dimensional reduced representation. Two simulated scenarios, a satellite reconfiguration maneuver and asteroid surface sampling, are developed to illustrate the approach. In addition, a simple two-dimensional experimental testbed consisting of an air-bearing table and two CubeSat engineering models is developed for partial testing and integration of the proposed methods.https://resolver.caltech.edu/CaltechAUTHORS:20140626-094453645Manufacture of Arbitrary Cross-Section Composite Honeycomb Cores Based on Origami Techniques
https://resolver.caltech.edu/CaltechAUTHORS:20140509-130505268
Year: 2014
DOI: 10.1115/1.4026824
As observed in the design of antenna reflectors and rocket bodies, both flat and 3D-shaped honeycomb cores are used in the field of aerospace engineering. This study illustrates
a new strategy to fabricate arbitrary cross-section honeycombs with applications of advanced composite materials by using the concept of the kirigami honeycomb, which is made from single flat sheets and has periodical slits resembling origami. The authors also describe a method of applying this technique to advanced composite materials.
Applying the partially soft composite techniques, 3D shaped composite honeycombs are manufactured, and some typical samples are shown with their folding line diagrams.https://resolver.caltech.edu/CaltechAUTHORS:20140509-130505268Optimization of Electrode Configuration in Surface-Parallel Actuated Deformable Mirrors
https://resolver.caltech.edu/CaltechAUTHORS:20151013-130020372
Year: 2014
DOI: 10.1117/12.2056495
Thin, lightweight and low-cost deformable mirrors have been recently proposed, providing a pertinent device for wavefront error correction. We present different approaches to optimize actuator arrangement. The design is optimized according to a given correction requirement, through the number of electrodes, their shape and location. A first method focuses on the compensation of a given optical aberration (astigmatism). A second method directly optimizes the correction of a set of optical modes, taking into account the voltage limitation. We will describe the optimization techniques and give some examples of applications and design performance.https://resolver.caltech.edu/CaltechAUTHORS:20151013-130020372Design, fabrication and testing of active carbon shell mirrors for space telescope applications
https://resolver.caltech.edu/CaltechAUTHORS:20150616-134615567
Year: 2014
DOI: 10.1117/12.2056560
A novel active mirror concept based on carbon fiber reinforced polymer (CFRP) materials is presented. A nanolaminate facesheet, active piezoelectric layer and printed electronics are implemented in order to provide the reflective surface, actuation capabilities and electrical wiring for the mirror. Mirrors of this design are extremely thin (500-850 µm), lightweight (~ 2 kg/m^2) and have large actuation capabilities (~ 100 µm peak- to-valley deformation per channel). Replication techniques along with simple bonding/transferring processes are implemented eliminating the need for grinding and polishing steps. An outline of the overall design, component materials and fabrication processes is presented. A method to size the active layer for a given mirror design, along with simulation predictions on the correction capabilities of the mirror are also outlined. A custom metrology system used to capture the highly deformable nature of the mirrors is demonstrated along with preliminary prototype measurements.https://resolver.caltech.edu/CaltechAUTHORS:20150616-134615567Packaging and deployment strategies for synthetic aperture radar membrane antenna arrays
https://resolver.caltech.edu/CaltechAUTHORS:20190814-104606776
Year: 2014
DOI: 10.1109/ursigass.2014.6929611
The performance of spaceborne synthetic aperture radar (SAR) is limited by the size and therefore the areal density of the antenna array. Conventional arrays consist of radiating elements mounted on hinged panels that are relatively heavy. In order to produce larger arrays capable of operating at higher altitudes, or to support comparable SAR payloads on smaller spacecraft, a lighter structure such as one using membranes must be used. Membrane antenna arrays have been developed, but deployment remains a challenge. This paper describes possible techniques to package and deploy membrane structures that can support these antenna arrays.https://resolver.caltech.edu/CaltechAUTHORS:20190814-104606776A Robotically-Assembled 100-Meter Space Telescope
https://resolver.caltech.edu/CaltechAUTHORS:20191017-082538614
Year: 2014
The future of astronomy may rely on extremely large space telescopes in order to image Earth-sized exoplanets or study the first stars. These telescopes will not be possible without a radical shift in design methods and concepts that are not limited by the size of a single payload fairing. In-Space Telescope Assembly Robotics (ISTAR) is one solution. The ISTAR project has developed a concept for an optical space telescope with a collecting area of nearly 8000 square meters, launched in pieces from the ground, and assembled by highly dexterous robots in space. The concept has been demonstrated to meet optical requirements and failure criteria.
This paper focuses on the design and feasibility analysis of the telescope structure, as it has to be stiff and precise enough to maintain optical tolerances while also being amenable to robotic operations. The overall optical scheme of the telescope is first presented, which includes four main elements: a spherical primary mirror roughly hexagonal in shape spanning 100 meters flat to flat; an eyepiece containing all subsequent mirrors and detectors; a metrology system; and a sun shade. The conceived structure that connects and supports these components is then detailed, beginning with the concept of operations and assembly process and ending with the results of a comprehensive structural analysis. Particular attention is given to the truss structure that supports the primary mirror segments, called the backplane. The backplane design uses both robotic assembly and deployable structures to reduce assembly time, featuring expanding truss modules grouped with pre-assembled clusters of mirror segments that are connected together in space. The truss geometry of the structure was chosen from a vast design space, which was first narrowed using "back-of-the-envelope" analytical methods, to satisfy vibrational stiffness and mass criteria. Higher fidelity simulations using finite element analysis and matrix methods were then used to demonstrate that the structure meets optical and failure strength requirements while subjected to loads typically encountered in the space environment.
This paper includes many of the decisions and trades made throughout the activity, providing a reference for the design of large modular space structures and laying the groundwork for future flight missions of this nature.https://resolver.caltech.edu/CaltechAUTHORS:20191017-082538614Using CubeSat/Micro-Satellite Technology to Demonstrate the Autonomous Assembly of a Reconfigurable Space Telescope (AAReST)
https://resolver.caltech.edu/CaltechAUTHORS:20190924-081804330
Year: 2014
Future space telescopes with diameter over 20 m will require new approaches: either high-precision formation flying or in-orbit assembly. We believe the latter holds promise as a potentially lower cost and more practical solution in the near term, provided much of the assembly can be carried out autonomously. To gain experience, and to provide risk reduction, we propose a combined mico/nano-satellite demonstration mission that will focus on the required optical technology (adaptive mirrors, phase-sensitive detectors) and autonomous rendezvous and docking technology (inter-satellite links, relative position sensing, automated docking mechanisms). The mission will involve two "3U" Cubesat-like nanosatellites ("MirrorSats") each carrying an electrically actuated adaptive mirror, and each capable of autonomous un-docking and re-docking with a small central "15U" class micro/nano-satellite core, which houses two fixed mirrors and a boom-deployed focal plane assembly. All three spacecraft will be launched as a single ~40kg micro-satellite package.
The spacecraft busses are based on heritage from Surrey's SNAP-1 and STRaND-1 missions (launched in 2000 and 2013 respectively), whilst the optics, imaging sensors and shape adjusting adaptive mirrors (with their associated adjustment mechanisms) are provided by CalTech/JPL. The spacecraft busses provide precise orbit and attitude control, with inter-satellite links and optical navigation to mediate the docking process. The docking system itself is based on the electromagnetic docking system being developed at the Surrey Space Centre (SSC), together with rendezvous sensing technology developed for STRaND-2. On orbit, the mission profile will firstly establish the imaging capability of the compound spacecraft before undocking, and then autonomously re-docking a single MirrorSat. This will test the docking system, autonomous navigation and system identification technology. If successful, the next stage will see the two MirrorSat spacecraft undock and re-dock to the core spacecraft in a linear formation to represent a large (but sparse) aperture for high resolution imaging. The imaging of stars is the primary objective, but other celestial and terrestrial targets are being considered. Teams at CalTech and SSC are currently working on the mission planning and development of space hardware. The autonomous rendezvous and docking system is currently under test on a 2D air-bearing table at SSC, and the propulsion and precision attitude control system is currently in development. Launch is planned for 2015. This paper details the mission concept, technology involved and progress to date.https://resolver.caltech.edu/CaltechAUTHORS:20190924-081804330Design of Ultrathin Composite Self-Deployable Booms
https://resolver.caltech.edu/CaltechAUTHORS:20150105-090948670
Year: 2014
DOI: 10.2514/1.A32815
Recently developed analysis techniques for thin shells that can be folded elastically and are able to self-deploy are used to develop an iterative design approach for this type of structure. The proposed approach considers a series of potential designs and then evaluates, for each trial design, key performance parameters through a complete simulation of its folding and deployment behavior. This design approach is applied to a boom concept consisting of a thin-walled tube in which two tape-spring hinges are made by cutting diametrically opposite slots; the geometry of the slots is fully defined by the length, width, and end diameter of the cuts. A design for a two-hinge, 1-m-long, lightweight self-deployable boom that can be wrapped around a small spacecraft is developed; the hinge geometry is chosen such that there is no damage during folding/deployment of the boom, and also the boom becomes latched at the first attempt. The chosen boom design is successfully validated experimentally.https://resolver.caltech.edu/CaltechAUTHORS:20150105-090948670Folding and Deployment of Thin Shell Structures
https://resolver.caltech.edu/CaltechAUTHORS:20170615-080812634
Year: 2015
DOI: 10.1007/978-3-7091-1877-1_5
Thin shells made of high modulus material are widely used as lightweight deployable space structures. The focus of this chapter is the most basic deployable thin shell structure, namely a straight, transversely curved strip known as a tape spring. Following a review of the materials used for the construction of deployable thin shell structures, including constitutive models and failure criteria developed specifically for this type of structures, this chapter provides an introduction to the mechanics of tape springs and tape spring hinges. Finite element techniques to model deployable structures containing tape springs are presented and the ability of these models to accurately simulate experimentally observed behavior is demonstrated. These tools can be used to design structures able to achieve specific behaviors. As an example, the design of a two-hinge boom that can be wrapped around a small spacecraft without any damage, and can dynamically deploy and smoothly latch into the deployed configuration is presented.https://resolver.caltech.edu/CaltechAUTHORS:20170615-080812634Dual-Matrix Composite Wideband Antenna Structures for CubeSats
https://resolver.caltech.edu/CaltechAUTHORS:20190816-144341792
Year: 2015
DOI: 10.2514/6.2015-0944
A concept for a deployable high-performance antenna for CubeSats is presented. The detailed design of a conical log-spiral antenna with wideband operation between 250 500 MHz, a gain of above 5 dB, and circular polarization is performed using electromagnetic simulations. A structural concept using dual-matrix composites with soft hinge regions, allowing the antenna to be packaged into small volumes, is developed. An antenna prototype is fabricated using Astroquartz fibers in an epoxy matrix; a high-strain silicone matrix is used in the hinge regions. Structural and electromagnetic analyses are conducted and show good agreement with predicted performance thus demonstrating the validity of the proposed antenna concept.https://resolver.caltech.edu/CaltechAUTHORS:20190816-144341792Large-Strain Viscoelastic Constitutive Models for Thin Polyethylene Films
https://resolver.caltech.edu/CaltechAUTHORS:20190816-144341701
Year: 2015
DOI: 10.2514/6.2015-0194
This paper presents a constitutive model capable of predicting the thermoviscoelastic behavior of the balloon thin film StratoFilm subject to large strains up to yielding. The model is based on the free volume theory of nonlinear thermoviscoelasticity and extended to orthotropic membranes. An ingredient of the present approach is that the experimentally inaccessible out-of-plane material properties are determined by fitting the model predictions to the measured non-linear behavior of the film. Creep tests, uniaxial tension tests, and biaxial bubble tests are used to determine the material parameters. The model has been validated experimentally, against data obtained from uniaxial tension tests and biaxial cylindrical tests at a wide range of temperatures and strain rates spanning two orders of magnitude (0.01%/s ~ 1%/s).https://resolver.caltech.edu/CaltechAUTHORS:20190816-144341701Spin-Stabilized Membrane Antenna Structures
https://resolver.caltech.edu/CaltechAUTHORS:20190816-144341883
Year: 2015
DOI: 10.2514/6.2015-1403
This paper explores the possibility of using spin-stabilized membrane structures for large phased array microwave antennas (typically L-Band or S-Band from 1 GHz to 4 GHz). The biggest challenge is to be able to sufficiently stabilize the system in order to limit its sensitivity to space disturbances (maneuvering, reaction wheels, and other imposed forces) and manufacturing imperfections. First, a flatness requirement for microwave antennas is derived. Then a frequency analysis of orthotropic flat structures spinning at different angular velocities and with different bending stiffnesses is carried out. These analyses, together with finite element simulations, are used to derive scaling laws to study the behavior of structures spinning in space. A test case, based on a spinning structure perturbed at the hub, is considered. An analytical solution of the free vibration of this test case is compared to the results of finite-element method simulations with Abaqus/Standard. Finally a test setup to study the dynamics of scaled spinning membranes in the laboratory is presented. Gravity effects in such an experiment are expected to be small.https://resolver.caltech.edu/CaltechAUTHORS:20190816-144341883Buckling Analysis of Axially Loaded Corrugated Cylindrical Shells
https://resolver.caltech.edu/CaltechAUTHORS:20190816-144341971
Year: 2015
DOI: 10.2514/6.2015-1435
Buckling analyses of heavily corrugated cylindrical shells based on detailed full finite element models are usually computationally expensive. To address this issue, we have pro- posed an efficient computational method of predicting the onset of buckling for corrugated cylindrical shells which builds on the Bloch wave method for infinitely periodic structures. We modified the traditional Bloch wave method in order to analyze the buckling of rotationally periodic shell structures. We have developed an efficient algorithm to perform our modified Bloch wave method. The buckling behavior of composite corrugated cylindrical shells with a range of numbers of corrugations was analyzed. Linear and nonlinear buckling analyses of detailed full finite element models were also performed and compared to our method. Comparisons showed that our modified Bloch wave method was able to obtain highly accurate buckling loads and it was able to capture both global and local buckling modes. It was also found that the computational time required by our modified Bloch wave method did not scale up as the number of corrugations increased.https://resolver.caltech.edu/CaltechAUTHORS:20190816-144341971Wrapping Thick Membranes with Slipping Folds
https://resolver.caltech.edu/CaltechAUTHORS:20190816-144340621
Year: 2015
DOI: 10.2514/6.2015-0682
A novel method of packaging finite-thickness membranes tightly and with high packaging efficiency is presented. This method allows the membrane to be packaged without extension and without plastic creasing. As such, initially flat membranes can be deployed to a flat state. Membrane thickness is accommodated by removing material along fold lines and exploiting the slipping deformation mechanism thus created.
Also presented are methods for prestressing and deploying membranes packaged according to this technique. Initial tests demonstrate packaging efficiencies of 73% without plastic deformation. Experimental deployment tests of a meter-scale model showed controlled deployment with unfolding forces of less than 0.6 N.https://resolver.caltech.edu/CaltechAUTHORS:20190816-144340621Design algorithm for the placement of identical segments in a large spherical mirror
https://resolver.caltech.edu/CaltechAUTHORS:20150402-133733867
Year: 2015
DOI: 10.1117/1.JATIS.1.2.024002
We present a design algorithm to compute the positions of identical, hexagonal mirror segments on a spherical surface, which is shown to provide a small variation in gap width. A one-dimensional analog to the segmentation problem is developed in order to motivate the desired configuration of the tiling patterns and to emphasize the desire for minimizing segment gap widths to improve optical performance. Our azimuthal equidistant centroid tiling algorithm is applied to three telescope architectures and produces mirror segment arrangements that compare favorably with existing and alternative designs.https://resolver.caltech.edu/CaltechAUTHORS:20150402-133733867Viscoplastic tearing of polyethylene thin film
https://resolver.caltech.edu/CaltechAUTHORS:20150706-104549692
Year: 2015
DOI: 10.1007/s11043-015-9259-7
Recent advances in noncontact strain measurement techniques and large-strain constitutive modeling of the linear low-density polyethylene film used in NASA superpressure balloons StratoFilm 420 are combined to provide a novel measurement technique for the tear propagation critical value of the J-integral. Previously these measurements required complex test configurations and procedures. It is found that the critical value of the J-integral increases by approximately 50 % when the strain rate is decreased from 1.33×10^−4 s^−1 to 1.33×10^−5 s^−1. It is shown that there is good correlation between measurements made on uniaxially loaded dogbone samples and circular diaphragms loaded by pressure, both with a 2-mm-wide slit in the middle. This result indicates that more extensive studies of strain-rate dependence may be made with the simpler, uniaxial test configuration.https://resolver.caltech.edu/CaltechAUTHORS:20150706-104549692Random Surface Texturing of mc-Silicon for Solar Cells with Picosecond Lasers; a Comparison between 1064 nm, 532 nm and 355 nm Laser Emission Wavelengths
https://resolver.caltech.edu/CaltechAUTHORS:20191002-150220868
Year: 2015
DOI: 10.1364/cleo_at.2015.am2k.5
Multicrystalline Silicon was textured with picosecond laser. Different laser wavelengths (λ = 1064, 532, 355 nm) where compared regarding laser-induced damage. We found that λ = 355 nm picosecond radiation resulted in shallower defect-reach region.https://resolver.caltech.edu/CaltechAUTHORS:20191002-150220868Optimized actuators for ultrathin deformable primary mirrors
https://resolver.caltech.edu/CaltechAUTHORS:20150520-080116235
Year: 2015
DOI: 10.1364/AO.54.004937
A novel design and selection scheme for surface-parallel actuators for ultrathin, lightweight mirrors is presented. The actuation system consists of electrodes printed on a continuous layer of piezoelectric material bonded to an optical-quality substrate. The electrodes provide almost full coverage of the piezoelectric layer, in order to maximize the amount of active material that is available for actuation, and their shape is optimized to maximize the correctability and stroke of the mirror for a chosen number of independent actuators and for a dominant imperfection mode. The starting point for the design of the electrodes is the observation that the correction of a figure error that has at least two planes of mirror symmetry is optimally done with twin actuators that have the same optimized shape but are rotated through a suitable angle. Additional sets of optimized twin actuators are defined by considering the intersection between the twin actuators, and hence an arbitrarily fine actuation pattern can be generated. It is shown that this approach leads to actuator systems with better performance than simple, geometrically based actuators. Several actuator patterns to correct third-order astigmatism aberrations are presented, and an experimental demonstration of a 41-actuator mirror is also presented.https://resolver.caltech.edu/CaltechAUTHORS:20150520-080116235Imperfection-insensitive axially loaded thin cylindrical shells
https://resolver.caltech.edu/CaltechAUTHORS:20150604-080335187
Year: 2015
DOI: 10.1016/j.ijsolstr.2014.12.030
The high efficiency of circular monocoque cylindrical shells in carrying axial loads is impaired by their extreme sensitivity to imperfections and there is an extensive body of literature that addresses this behavior. Instead of following this classical path, focused on circular cross-sections, this paper presents a novel approach that adopts optimal symmetry-breaking wavy cross-sections (wavy shells). The avoidance of imperfection sensitivity is achieved by searching with an evolutionary algorithm for smooth cross-sectional shapes that maximize the minimum among the buckling loads of geometrically perfect and imperfect wavy shells. It is found that shells designed through this approach can achieve higher critical stresses and knockdown factors than any previously known monocoque cylindrical shells. It is also found that these shells have superior mass efficiency to almost all previously reported stiffened shells.https://resolver.caltech.edu/CaltechAUTHORS:20150604-080335187A New UHF Deployable Antenna for CubeSats
https://resolver.caltech.edu/CaltechAUTHORS:20160401-100827980
Year: 2015
DOI: 10.1109/APS.2015.7305102
This paper discusses the design of a new conical log spiral antenna that can operate at UHF frequencies. The antenna constitutes a suitable candidate for deployment on top of a 6U CubeSat system. The conical log spiral is designed to operate between 300 MHz and 600 MHz and exhibit circular polarization as well as an acceptable gain. The antenna is also required to satisfy size constraints by being compactly folded during launch and deployed successfully once in orbit.https://resolver.caltech.edu/CaltechAUTHORS:20160401-100827980Using CubeSat/micro-satellite technology to demonstrate the Autonomous Assembly of a Reconfigurable Space Telescope (AAReST)
https://resolver.caltech.edu/CaltechAUTHORS:20150806-141005388
Year: 2015
DOI: 10.1016/j.actaastro.2015.04.008
Future space telescopes with diameter over 20 m will require new approaches: either high-precision formation flying or in-orbit assembly. We believe the latter holds promise at a potentially lower cost and more practical solution in the near term, provided much of the assembly can be carried out autonomously. To gain experience, and to provide risk reduction, we propose a combined micro/nano-satellite demonstration mission that will focus on the required optical technology (adaptive mirrors, phase-sensitive detectors) and autonomous rendezvous and docking technology (inter-satellite links, relative position sensing, automated docking mechanisms). The mission will involve two "3U" CubeSat-like nanosatellites ("MirrorSats") each carrying an electrically actuated adaptive mirror, and each capable of autonomous un-docking and re-docking with a small central "15U" class micro/nano-satellite core, which houses two fixed mirrors and a boom-deployed focal plane assembly. All three spacecrafts will be launched as a single ~40 kg micro-satellite package. The spacecraft busses are based on heritage from Surrey׳s SNAP-1 and STRaND-1 missions (launched in 2000 and 2013 respectively), whilst the optics, imaging sensors and shape adjusting adaptive mirrors (with their associated adjustment mechanisms) are provided by CalTech/JPL. The spacecraft busses provide precise orbit and attitude control, with inter-satellite links and optical navigation to mediate the docking process. The docking system itself is based on the electromagnetic docking system being developed at the Surrey Space Centre (SSC), together with rendezvous sensing technology developed for STRaND-2. On orbit, the mission profile will firstly establish the imaging capability of the compound spacecraft before undocking, and then autonomously re-docking a single MirrorSat. This will test the docking system, autonomous navigation and system identification technology. If successful, the next stage will see the two MirrorSat spacecraft undock and re-dock to the core spacecraft in a linear formation to represent a large (but sparse) aperture for high resolution imaging. The imaging of stars is the primary objective, but other celestial and terrestrial targets are being considered. Teams at CalTech and SSC are currently working on the mission planning and development of space hardware. The autonomous rendezvous and docking system is currently under test on a 2D air-bearing table at SSC, and the propulsion and precision attitude control system is currently in development. Launch is planned for 2016. This paper details the mission concept; technology involved and progress to date, focussing on the spacecraft buses.https://resolver.caltech.edu/CaltechAUTHORS:20150806-141005388Membrane Spin Up in a Normal Gravity Field: Experiments and Simulations
https://resolver.caltech.edu/CaltechAUTHORS:20160930-131912958
Year: 2016
DOI: 10.2514/6.2016-1216
Finite element simulations and experimental observations of the spin up in vacuum of a thin membrane loaded by gravity are presented. The numerical techniques take into account the run time of each simulation and energy convergence; it is shown that accurate results can be obtained quite quickly in a rotating reference frame, and that including stiffness-proportional material damping helps convergence of the integration. It is also found that a very fine finite element mesh around the hub of the membrane is required to obtain consistent results. The experimental setup allows spinning of the membrane in a vacuum box; a measurement technique that uses stereo Digital Image Correlation is presented. A comparison between experiments and simulations using characteristic parameters of the shape of a membrane, i.e. the number of rotational symmetric waves, the average deflection, and the elastic bending strain energy of the membrane, shows good agreement between experiments and simulations.https://resolver.caltech.edu/CaltechAUTHORS:20160930-131912958A Deployable Vivaldi-fed Conical Horn Antenna for CubeSats
https://resolver.caltech.edu/CaltechAUTHORS:20160909-112312357
Year: 2016
DOI: 10.1109/USNC-URSI-NRSM.2016.7436244
The advent of CubeSats has revolutionized the space research industry. The small physical size and constraints owing to outer space applications present significant challenges for antenna engineers to come up with innovative solutions. This paper presents a novel wide band antenna high gain antenna which is capable of deploying from a CubeSat platform.https://resolver.caltech.edu/CaltechAUTHORS:20160909-112312357Effects of Long-Term Stowage on the Deployment of Bistable Tape Springs
https://resolver.caltech.edu/CaltechAUTHORS:20160408-093030473
Year: 2016
DOI: 10.1115/1.4031618
In the context of strain-energy-deployed space structures, material relaxation effects play a significant role in structures that are stowed for long durations, for example, in a space vehicle prior to launch. Here, the deployment of an ultrathin carbon fiber reinforced plastic (CFRP) tape spring is studied, with the aim of understanding how long-duration stowage affects its deployment behavior. Analytical modeling and experiments show that the deployment time increases predictably with stowage time and temperature, and analytical predictions are found to compare well with experiments. For cases where stress relaxation is excessive, the structure is shown to lose its ability to deploy autonomously.https://resolver.caltech.edu/CaltechAUTHORS:20160408-093030473Methods for Characterizing the Reliability of Deployable Modules for Large Optical Reflectors
https://resolver.caltech.edu/CaltechAUTHORS:20160930-132028713
Year: 2016
DOI: 10.2514/6.2016-2164
The In-Space Telescope Assembly Robotics (ISTAR) project has proposed an architecture for a large robotically-assembled telescope in space, comprised of many deployable truss modules. The truss modules are based on the Pactruss deployment scheme and are equipped with Rolamite tape spring hinges. Fabrication and assembly errors that arise from bulk manufacturing the modules may make the deployment unreliable. A simulation toolkit has been developed to characterize the deployment behavior of the module in the presence of such errors. This paper first outlines the details of the toolkit, including the truss model, the Rolamite hinge model, and the simulation methodology. It then describes the experiment designed to validate the toolkit. A module was constructed and deployed while tracking the displacements of a select node and the rotations of the Rolamite hinges. The measured shape of this module was recreated in the simulation model and the same parameters were obtained. It was found that the experimental and simulated nodal displacements matched within 10%. The experimental hinge behavior was generally captured in the simulation, with some discrepancies in the latching of one hinge. The possible causes for the discrepancies and ongoing work to improve the results are discussed in the paper.https://resolver.caltech.edu/CaltechAUTHORS:20160930-132028713Ultralight Structures for Space Solar Power Satellites
https://resolver.caltech.edu/CaltechAUTHORS:20160930-131726070
Year: 2016
DOI: 10.2514/6.2016-1950
The design of a deployable spacecraft, measuring 60 m × 60 m, and with an areal density 100 g m^(−2) , is described. This spacecraft can be packaged into a cylinder measuring 1.5 m in height and 1 m in diameter. It can be deployed to a flat configuration, where it acts as a stiff, lightweight support framework for multifunctional tiles that collect sunlight, generate electric power, and transmit to a ground station on Earth.https://resolver.caltech.edu/CaltechAUTHORS:20160930-131726070Folding and Deployment of Closed Cross-Section Dual-Matrix Composite Booms
https://resolver.caltech.edu/CaltechAUTHORS:20190828-095135682
Year: 2016
DOI: 10.2514/6.2016-0970
A dual-matrix composite boom is proposed as a way of realizing a deployable closed cross-section boom that is stiff, lightweight, and can be packaged in small volumes. Little work exists studying the folding and deployment behavior of closed cross-section boom made of composite shells and this paper addresses this by investigating the behavior for two closed cross-section designs. Experimental techniques for measuring the folded shape of curved shells undergoing large deformations is presented. Furthermore, experimental measurements of the moment-rotation response of the two booms are discussed. A study using commercially available finite element software yields simulation techniques for successfully
predicting the folded shape of closed-cross section booms. The drawbacks of the software when predicting the moment-rotation response are addressed. The application of these techniques for the chosen designs demonstrate that dual-matrix booms are a promising alternative to existing composite deployable booms.https://resolver.caltech.edu/CaltechAUTHORS:20190828-095135682Adaptive Multi-Functional Space Systems for Micro-Climate Control
https://resolver.caltech.edu/CaltechAUTHORS:20160106-111503640
Year: 2016
DOI: 10.26206/6SCT-RJ67
This report summarizes the work done during the Adaptive Multifunctional Systems for Microclimate
Control Study held at the Caltech Keck Institute for Space Studies (KISS) in 2014-2015.
Dr. Marco Quadrelli (JPL), Dr. James Lyke (AFRL), and Prof. Sergio Pellegrino (Caltech) led
the Study, which included two workshops: the first in May of 2014, and another in February
of 2015. The Final Report of the Study presented here describes the potential relevance of
adaptive multifunctional systems for microclimate control to the missions outlined in the 2010
NRC Decadal Survey.
The objective of the Study was to adapt the most recent advances in multifunctional reconfigurable
and adaptive structures to enable a microenvironment control to support space exploration in
extreme environments (EE). The technical goal was to identify the most efficient materials,
architectures, structures and means of deployment/reconfiguration, system autonomy and energy
management solutions needed to optimally project/generate a micro-environment around space
assets. For example, compact packed thin-layer reflective structures unfolding to large areas
can reflect solar energy, warming and illuminating assets such as exploration rovers on Mars or
human habitats on the Moon. This novel solution is called an energy-projecting multifunctional
system (EPMFS), which are composed of Multifunctional Systems (MFS) and Energy-Projecting
Systems (EPS).https://resolver.caltech.edu/CaltechAUTHORS:20160106-111503640Thermoviscoelastic models for polyethylene thin films
https://resolver.caltech.edu/CaltechAUTHORS:20151116-102001293
Year: 2016
DOI: 10.1007/s11043-015-9282-8
This paper presents a constitutive thermoviscoelastic model for thin films of linear low-density polyethylene subject to strains up to yielding. The model is based on the free volume theory of nonlinear thermoviscoelasticity, extended to orthotropic membranes. An ingredient of the present approach is that the experimentally inaccessible out-of-plane material properties are determined by fitting the model predictions to the measured nonlinear behavior of the film. Creep tests, uniaxial tension tests, and biaxial bubble tests are used to determine the material parameters. The model has been validated experimentally, against data obtained from uniaxial tension tests and biaxial cylindrical tests at a wide range of temperatures and strain rates spanning two orders of magnitude.https://resolver.caltech.edu/CaltechAUTHORS:20151116-102001293Multilayer Active Shell Mirrors for Space Telescopes
https://resolver.caltech.edu/CaltechAUTHORS:20160929-102853368
Year: 2016
DOI: 10.1117/12.2233594
A novel active mirror technology based on carbon fiber reinforced polymer (CFRP) substrates and replication techniques has been developed. Multiple additional layers are implemented into the design serving various functions. Nanolaminate metal films are used to provide a high quality reflective front surface. A backing layer of thin active material is implemented to provide the surface-parallel actuation scheme. Printed electronics are used to create a custom electrode pattern and flexible routing layer. Mirrors of this design are thin (< 1.0 mm), lightweight (2.7 kg/m^2), and have large actuation capabilities. These capabilities, along with the associated manufacturing processes, represent a significant change in design compared to traditional optics. Such mirrors could be used as lightweight primaries for small CubeSat-based telescopes or as meter-class segments for future large aperture observatories. Multiple mirrors can be produced under identical conditions enabling a substantial reduction in manufacturing cost and complexity.
An overview of the mirror design and manufacturing processes is presented. Predictions on the actuation performance have been made through finite element simulations demonstrating correctabilities on the order of 250-300× for astigmatic modes with only 41 independent actuators. A description of the custom metrology system used to characterize the active mirrors is also presented. The system is based on a Reverse Hartmann test and can accommodate extremely large deviations in mirror figure (> 100 μm PV) down to sub-micron precision. The system has been validated against several traditional techniques including photogrammetry and interferometry. The mirror performance has been characterized using this system, as well as closed-loop figure correction experiments on 150 mm dia. prototypes. The mirrors have demonstrated post-correction figure accuracies of 200 nm RMS (two dead actuators limiting performance).https://resolver.caltech.edu/CaltechAUTHORS:20160929-102853368Nondestructive Mapping of Hybrid Rocket Fuel Grains
https://resolver.caltech.edu/CaltechAUTHORS:20190822-102905667
Year: 2016
DOI: 10.2514/6.2016-4866
The regression rates of solid fuels used in hybrid rocket motors are a critical parameter in the design and development of hybrid propulsion systems. Currently, it is difficult to measure fuel geometries accurately, thus causing difficulties in accurately describing regression rates, especially for smaller scale systems. Nondestructive techniques can solve this problem, as it is not necessary to get tooling into the ports. An apparatus that maps the fuel grain employing an immersed ultrasound transducer has been manufactured; its results will be the primary focus of this study. The full geometry of the fuel grains can be generated pre and post fire, which may lead to greater understanding of the way hybrid rocket fuels burn. Furthermore, previously undetectable defects, such as cracks and voids, may be identified. The study found that the method used to cast the fuel grains, spin casting causes thinning in wall thickness on average of 11.3% with a standard deviation of 1.2% from the end to the middle of the fuel grain. The generated data can further validate proposed analytical solutions (Cantwell, 2014) to the regression rate equations (Marxman and Gilbert, 1963) associated with hybrid rocket propulsion systems.https://resolver.caltech.edu/CaltechAUTHORS:20190822-102905667Co-phasing primary mirror segments of an optical space telescope using a long stroke Zernike WFS
https://resolver.caltech.edu/CaltechAUTHORS:20160929-095806840
Year: 2016
DOI: 10.1117/12.2249638
Static Zernike phase-contrast plates have been used extensively in microscopy for half a century and, more recently, in optical telescopes for wavefront sensing. A dynamic Zernike wavefront sensor (WFS) with four phase shifts, for reducing error due to spurious light and eliminating other asynchronous noise, has been proposed for use in adaptive optics. Here, we propose adapting this method for co-phasing the primary mirror of a segmented space telescope. In order to extend the dynamic range of the WFS, which has a maximum range of +/ − λ/2, a phase- contrast plate with multiple steps, both positive and negative, has been developed such that errors as large as +/ − 10λ can be sensed. The manufacturing tolerances have been incorporated into simulations, which demonstrate that performance impacts are minimal. We show that the addition of this small optical plate along with a high precision linear translation stage at the prime focus of a telescope and pupil viewing capability can provide extremely accurate segment phasing with a simple white-light fringe fitting algorithm and a closed-loop controller. The original focal-plane geometry of a centro-symmetric phase shifting element is replaced with a much less constrained shape, such as a slot. Also, a dedicated pupil imager is not strictly required; an existing pupil sampler such as a Shack-Hartmann (SH) WFS can be used just as effectively, allowing simultaneous detection of wavefront errors using both intensity and spot positions on the SH-WFS. This could lead to an efficient synergy between Zernike and SH-WFS, enabling segment phasing in conjunction with high-dynamic range sensing.https://resolver.caltech.edu/CaltechAUTHORS:20160929-095806840UHF Deployable Helical Antennas for CubeSats
https://resolver.caltech.edu/CaltechAUTHORS:20160913-085506285
Year: 2016
DOI: 10.1109/TAP.2016.2583058
The design process and the deployment mechanism of a quadrifilar helix antenna (QHA) and a conical log spiral antenna (CLSA) are presented. The two antennas are proposed to operate in the UHF frequency band. They are composed of conductors that are embedded and supported by innovative structural techniques. This allows efficient folding, packaging, and deployment once in space. The conductors in the QHA are composed of beryllium copper and are supported by helical arms of S_2 glass fiber reinforced epoxy. The CLSA, on the other hand, has conductors that are made out of a mesh of phosphor bronze and incorporated inside thin insulators composed of continuous fiber composites. The new aspects of these designs lie in their structures and deployment mechanisms. The deployment mechanisms for both antennas include helical pantograph and origami patterns such as Z-folding configurations. Both antennas are fabricated and tested for both deployment and radiation performance. A comparison is executed between both designs, and their potential deployment possibilities from CubeSats are also investigated.https://resolver.caltech.edu/CaltechAUTHORS:20160913-085506285Architecture for in-space robotic assembly of a modular space telescope
https://resolver.caltech.edu/CaltechAUTHORS:20160713-105905208
Year: 2016
DOI: 10.1117/1.JATIS.2.4.041207
An architecture and conceptual design for a robotically assembled, modular space telescope (RAMST) that enables extremely large space telescopes to be conceived is presented. The distinguishing features of the RAMST architecture compared with prior concepts include the use of a modular deployable structure, a general-purpose robot, and advanced metrology, with the option of formation flying. To demonstrate the feasibility of the robotic assembly concept, we present a reference design using the RAMST architecture for a formation flying 100-m telescope that is assembled in Earth orbit and operated at the Sun–Earth Lagrange Point 2.https://resolver.caltech.edu/CaltechAUTHORS:20160713-105905208Nonlinear dynamic analysis of creased shells
https://resolver.caltech.edu/CaltechAUTHORS:20161111-101434125
Year: 2016
DOI: 10.1016/j.finel.2016.07.008
Recent studies analyze the behavior of advanced shell structures, like foldable, multistable or morphing shell structures. Simulating a thin foldable curved structure is not a trivial task: the structure may go through many snapping transitions from a stable configuration to another. Then, one could claim arc-length methods or use a dynamic approach to perform such simulations. This work presents a geometrically exact shell model for nonlinear dynamic analysis of shells. An updated Lagrangian framework is used for describing kinematics. Several numerical examples of folding a thin dome are presented, including creased shells. The triangular shell finite element used offers great flexibility for the generation of the unstructured curved meshes, as well as great results.https://resolver.caltech.edu/CaltechAUTHORS:20161111-101434125Bloch wave buckling analysis of axially loaded periodic cylindrical shells
https://resolver.caltech.edu/CaltechAUTHORS:20161202-074257153
Year: 2016
DOI: 10.1016/j.compstruc.2016.09.006
This paper presents an efficient computational method for predicting the onset of buckling of axially loaded, corrugated or stiffened cylindrical shells. This method is a modification of the Bloch wave method which builds on the stiffness matrix method. A numerical method and an efficient algorithm have been developed to implement the proposed method in the commercial finite element package Abaqus. Numerical examples have shown that, compared to the nonlinear buckling analyses based on detailed full finite element models, the proposed method can obtain highly accurate buckling loads and buckling modes and can achieve very significant reductions in computational time.https://resolver.caltech.edu/CaltechAUTHORS:20161202-074257153Micromechanics Models for Viscoelastic Plain-Weave Composite Tape Springs
https://resolver.caltech.edu/CaltechAUTHORS:20170216-123337810
Year: 2017
DOI: 10.2514/1.J055041
The viscoelastic behavior of polymer composites decreases the deployment force and the postdeployment shape accuracy of composite deployable space structures. This paper presents a viscoelastic model for single-ply cylindrical shells (tape springs) that are deployed after being held folded for a given period of time. The model is derived from a representative unit cell of the composite material, based on the microstructure geometry. Key ingredients are the fiber volume density in the composite tows and the constitutive behavior of the fibers (assumed to be linear elastic and transversely isotropic) and of the matrix (assumed to be linear viscoelastic). Finite-element-based homogenizations at two scales are conducted to obtain the Prony series that characterize the orthotropic behavior of the composite tow, using the measured relaxation modulus of the matrix as an input. A further homogenization leads to the lamina relaxation ABDABD matrix. The accuracy of the proposed model is verified against the experimentally measured time-dependent compliance of single lamina in either pure tension or pure bending. Finite element simulations of single-ply tape springs based on the proposed model are compared to experimental measurements that were also obtained during this study.https://resolver.caltech.edu/CaltechAUTHORS:20170216-123337810Modular Foldable Surfaces: a Novel Approach based on Spatial Mechanisms and Thin Shells
https://resolver.caltech.edu/CaltechAUTHORS:20190821-155916295
Year: 2017
DOI: 10.2514/6.2017-1345
This paper investigates a set of novel techniques that lead to modular, deployable surface arrays which could be either flat or curved in their deployed shape. The two components of the proposed concepts are thin shells with smooth folds and spatial mechanisms with rolling hinges. Kinematics of the mechanism and motion of the shell has been shown to be fully compatible with each other during folding and unfolding. This basic module is then articulated to create multiple modular tessellations, which form a series of foldable surfaces. We further demonstrate that curvature could be introduced to the initially flat shells using bonded piezoceramic actuators. The techniques and concepts proposed in this paper could be valuable for the design of future deployable space-based telescope and other reflective arrays which require high shape precision with low storage area and volume.https://resolver.caltech.edu/CaltechAUTHORS:20190821-155916295In-space Shape Measurement of Large Planar Structures
https://resolver.caltech.edu/CaltechAUTHORS:20190820-154603282
Year: 2017
DOI: 10.2514/6.2017-1116
A measurement and integration scheme is proposed to estimate the shape of a large planar structure in space. Lightweight sun sensors distributed on the structure measure the local angles relative to the sun. A reconstruction technique is introduced to estimate the shape of the satellite through a decomposition on a function basis. The estimated shape is determined by the coefficients associated with the basis functions which are calculated from the measurements. A trade-study to analyze the influence of different reconstruction schemes and the position of the sensors is presented. An optimization scheme minimizes the RMS error between the estimated and true shape. An experiment was conducted to show the feasibility and performance of the proposed system at the lab scale. Finally, a simulation of the accuracy of the presented solution on a 60 m space solar power module is performed. The expected error is 0.7 mm RMS using sensors every 30 cm.https://resolver.caltech.edu/CaltechAUTHORS:20190820-154603282Vibration Response of Ultralight Coilable Spacecraft Structures
https://resolver.caltech.edu/CaltechAUTHORS:20190820-152401055
Year: 2017
DOI: 10.2514/6.2017-1115
Dynamic assessment of ultralight wrapped spacecraft structures subject to the launch vibration environment is difficult, and has been foregone in many space programs in favor of purely experimental test campaigns. We present a numerical methodology to better understand the wrapped state of a structure and the dynamic behavior during launch vibration, enabling higher confidence in its survivability and greater understanding of the dynamic behavior at different scales, which vibration test approaches alone cannot achieve.https://resolver.caltech.edu/CaltechAUTHORS:20190820-152401055Characterization of Ultra-Thin Composite Triangular Rollable and Collapsible Booms
https://resolver.caltech.edu/CaltechAUTHORS:20190816-144341170
Year: 2017
DOI: 10.2514/6.2017-0172
The paper studies the behavior of Triangular Rollable and Collapsible (TRAC) booms made from ultra-thin carbon fiber, with a total flange thickness of 71 µm. Both bending and torsional behavior of the deployed booms are studied using numerical analysis and experimental testing. The coiling of the booms around hubs of large radius is also studied.https://resolver.caltech.edu/CaltechAUTHORS:20190816-144341170Trajectory design of formation flying constellation for space-based solar power
https://resolver.caltech.edu/CaltechAUTHORS:20170614-164611614
Year: 2017
DOI: 10.1109/AERO.2017.7943711
The concept of collecting solar power in space and transmitting it to the Earth using a microwave beam has appealed to the imagination of numerous researchers in the past. The Space Solar Power Initiative at Caltech is working towards turning this idea into reality, by developing the critical technologies necessary to make this an economically feasible solution. The proposed system comprises an array of ultralight, membrane-like deployable modules with high efficiency photovoltaics and microwave transmission antennas embedded in the structure. Each module is 60 m χ 60 m in size and in the final configuration, ∼2500 of these modules form a 3 km χ 3 km array in a geosynchronous orbit. As the constellation orbits the Earth, the orientation and position of each module has to be changed so as to optimize the angle made by the photovoltaic surface with respect to the sun and by the antenna surface with respect to the receiving station on Earth. We derive the optimum orientation profile for the modules and find that modules with dual-sided RF transmission can provide 1.5 times more orbit-averaged power than modules with single-sided RF transmission. To carry out the corresponding orbital maneuvers, an optimization framework using the Hill-Clohessy-Wiltshire (HCW) equations is developed to achieve the dual goal of maximizing the power delivered, while minimizing the propellant required to carry out the desired orbital maneuvers. Results are presented for a constellation with modules in fixed relative positions and also for a constellation where the modules execute circularized periodic relative motion in the HCW frame. We show that the use of these periodic relative orbits reduces the propellant consumption from ∼150 kg to ∼50 kg. This drastic reduction makes the propellant mass a significantly smaller fraction of the module's dry mass (370 kg), thereby solving a major technical hurdle in the realization of space-based solar power.https://resolver.caltech.edu/CaltechAUTHORS:20170614-164611614Crease-free biaxial packaging of thick membranes with slipping folds
https://resolver.caltech.edu/CaltechAUTHORS:20170407-080803700
Year: 2017
DOI: 10.1016/j.ijsolstr.2016.08.013
This paper presents a novel scheme to biaxially package and deploy flat membranes, in which the thickness of the membrane is accounted for through the novel concept of slipping folds. The membrane is divided into parallel strips connected by slipping folds, and specially chosen wrapping profiles that require zero slip along the edges of the membrane are identified. This packaging scheme avoids the kinematic incompatibilities that in other schemes result in local buckles and wrinkles that increase the deployment force and permanently deform the membrane. The paper also presents a scheme to apply uniform uniaxial prestress to the deployed membrane, as well as a two-stage deployment scheme. Packaging efficiencies of up to 83% have been demonstrated for meter-scale models, although for large membranes the packaging efficiency approaches 100%.https://resolver.caltech.edu/CaltechAUTHORS:20170407-080803700Post-cure shape errors of ultra-thin symmetric CFRP laminates: Effect of ply-level imperfections
https://resolver.caltech.edu/CaltechAUTHORS:20170317-082612485
Year: 2017
DOI: 10.1016/j.compstruct.2016.12.075
This paper discusses the effect of misalignments in ply orientation, uniform variations in ply thickness, and through-thickness thermal gradients on the post-cure shape errors for symmetric cross-ply laminates constructed from ultra-thin composite materials. Photogrammetry-based surface measurements are performed for laminates cured at elevated temperatures. Significant out-of-plane shape errors are observed, with amplitudes ∼75 times the laminate thickness. The magnitude of each imperfection is also characterized experimentally on coupon-level samples. A non-linear finite element model is developed and demonstrates that these imperfections result in cylindrical and twisting modes of deformation. Results are compared to Classical Lamination Theory predictions which are shown to be inadequate in predicting shape errors that require changes in Gaussian curvature. Through these studies, it is determined that thickness variations between the top and bottom plies have the most pronounced effect on shape errors.https://resolver.caltech.edu/CaltechAUTHORS:20170317-082612485Rapid Design of Deployable Antennas for CubeSats: A tool to help designers compare and select antenna topologies
https://resolver.caltech.edu/CaltechAUTHORS:20170303-105701054
Year: 2017
DOI: 10.1109/MAP.2017.2655531
A novel methodology for the rapid preliminary design of
deployable antennas for CubeSats is proposed in this
article. It uses a graphical representation of antenna
performance, consisting of a set of plots of different
performance metrics against antenna geometry parameters.
Coupled electromagnetic and structural design problems are
addressed easily, enabling the rapid and direct comparison of different antenna concepts. This approach is demonstrated
for a case study at ultrahigh frequency (UHF), comparing
the performance of a dipole, a helix, a conical horn, and a
conical log spiral (CLS), all based on dual-matrix composite
deployable structures. The initial design space of antenna
geometries is reduced by two orders of magnitude to a set
of constraint-satisfying designs. A graphical user interface
implementing the approach is presented, and the accuracy of
the method is briefly addressed.https://resolver.caltech.edu/CaltechAUTHORS:20170303-105701054Lightweight Carbon Fiber Mirrors for Solar Concentrator Applications
https://resolver.caltech.edu/CaltechAUTHORS:20181109-075349019
Year: 2017
DOI: 10.48550/arXiv.1810.09529
Lightweight parabolic mirrors for solar concentrators have been fabricated using carbon fiber reinforced polymer (CFRP) and a nanometer scale optical surface smoothing technique. The smoothing technique improved the surface roughness of the CFRP surface from ~3 μm root mean square (RMS) for as-cast to ~5 nm RMS after smoothing. The surfaces were then coated with metal, which retained the sub-wavelength surface roughness, to produce a high-quality specular reflector. The mirrors were tested in an 11x geometrical concentrator configuration and achieved an optical efficiency of 78% under an AM0 solar simulator. With further development, lightweight CFRP mirrors will enable dramatic improvements in the specific power, power per unit mass, achievable for concentrated photovoltaics in space.https://resolver.caltech.edu/CaltechAUTHORS:20181109-075349019Near-unity ultra-wideband thermal infrared emission for space solar power radiative cooling
https://resolver.caltech.edu/CaltechAUTHORS:20181109-081714215
Year: 2017
DOI: 10.1109/PVSC.2017.8366597
We report the design, fabrication and characterization of ultrathin metasurfaces that exhibit wideband 300 K thermal emissivity. The emissive behavior of these structures is almost independent of the emission angle. Our ultralight subwavelength-thickness metasurfaces can be fabricated relatively easily and are excellent candidates for radiative cooling in space applications.https://resolver.caltech.edu/CaltechAUTHORS:20181109-081714215Design and Prototyping Efforts for the Space Solar Power Initiative
https://resolver.caltech.edu/CaltechAUTHORS:20181108-154443049
Year: 2017
DOI: 10.1109/PVSC.2017.8366621
The Space Solar Power Initiative (SSPI) seeks to enable reliable, cost-effective baseload power generation from large-scale solar power stations in space. We propose an ultralight, modular power station, having specific power in the range of 1–10 kW/kg for the photovoltaic (PV) collection subsystem. The building block of the power station is the 'tile,' a self-contained element that performs PV energy collection, conversion to radio frequency (RF), and transmission to earth. To minimize PV mass, we select a 1D, 10–20X parabolic trough concentrator geometry, which provides cooling and radiation shielding for the cells, and which folds flat for deployment. Here, we discuss the design, fabrication, and testing of the initial PV tile prototypes.https://resolver.caltech.edu/CaltechAUTHORS:20181108-154443049Trajectory Design of a Spacecraft Formation for Space-Based Solar Power Using Sequential Convex Programming
https://resolver.caltech.edu/CaltechAUTHORS:20170630-094657577
Year: 2017
The concept of collecting solar power in space and transmitting it to the Earth using microwaves has been studied by numerous researchers in the past. The Space Solar Power Initiative (SSPI) at Caltech is a collaborative project to bring about the scientific and technological innovations necessary for enabling a space-based solar power system. The proposed system comprises an array of ultra-light, membrane-like deployable modules with high efficiency photovoltaic (PV) concentrators and microwave transmission antennas embedded in the structure. Each module is 60m x 60m in size and in the final configuration, hundreds of these modules span a 3km x 3km array in a geosynchronous orbit. As this formation goes around the Earth, the orientation and position of each module has to be changed so as to optimize the angle made by the photovoltaic surface with respect to the sun and by the antenna surface with respect to the receiving station on Earth. In order to achieve high antenna array efficiency, the modules have to remain in a tight formation with an edge-to-edge distance on the order of a few meters. In addition, the modules also have to avoid collisions and maintain a planar configuration to avoid the possibility of both PV and RF shadowing. In this paper, we present the trajectory design that achieves the dual goal of minimizing the propellant usage and maximizing the power delivered to the ground station, while meeting the various orbital constraints. The optimal control problem is solved using sequential convex programming for a 4 x 4 formation and the results obtained show that it is possible to maintain the formation for 11 years in a geo-synchronous orbit with relatively small amounts of propellant. This serves as a critical achievement in the path towards realizing the objective of space-based solar power.https://resolver.caltech.edu/CaltechAUTHORS:20170630-094657577Impact of Space Radiation Environment on Concentrator Photovoltaic Systems
https://resolver.caltech.edu/CaltechAUTHORS:20181109-074226646
Year: 2017
DOI: 10.1109/PVSC.2017.8366020
Concentrator photovoltaic systems can provide supplementary shielding against high energy particles. In this paper we compare the radiation environment that the same solar cell would experience in a flat-plate module versus in a parabolic mirror concentrator system. We have observed that the shielding provided by the concentrator system is remarkable. In order to obtain an accurate prediction of the overall shield needed in our concentrator system triple-junction space solar cells have been irradiated on the edge with 350-keV protons at a fluence of 10^(12) p^+cm^(-2). A mild degradation of the open circuit voltage was measured (~70 mV).https://resolver.caltech.edu/CaltechAUTHORS:20181109-074226646Experiments on imperfection insensitive axially loaded cylindrical shells
https://resolver.caltech.edu/CaltechAUTHORS:20170526-080151216
Year: 2017
DOI: 10.1016/j.ijsolstr.2017.02.028
This paper presents an experimental study of imperfection insensitive composite wavy cylindrical shells subject to axial compression. A fabrication technique for making cylindrical shells with intricate shape of cross-sections has been developed. A photogrammetry technique to measure the geometric imperfections has also been developed. The behavior of the wavy shells under axial compression was predicted through simulations and measured through compression tests. Both the analyses and experiments have confirmed that the wavy shells are imperfection insensitive. Comparisons between the wavy shells and circular shells have also confirmed that introducing optimal symmetry-breaking wavy cross-sections can significantly reduce the imperfection sensitivity and improve the load-bearing capability of cylindrical shells.https://resolver.caltech.edu/CaltechAUTHORS:20170526-080151216Ultra-Thin Composite Deployable Booms
https://resolver.caltech.edu/CaltechAUTHORS:20191112-155802266
Year: 2017
Ultra-thin TRAC booms have many applications for spacecraft structures due to their very efficient packaging. A manufacturing process is proposed for composite TRAC booms with a total flange thickness of 71 μm. The mechanical behavior in both bending and torsion is studied through experiments.https://resolver.caltech.edu/CaltechAUTHORS:20191112-155802266Design of ultra-thin composite deployable shell structures through machine learning
https://resolver.caltech.edu/CaltechAUTHORS:20191114-160021163
Year: 2017
A data-driven computational framework is applied for the design of optimal ultra-thin Triangular Rollable and Collapsible (TRAC) carbon fiber booms. High-fidelity computational analyses of a large number of geometries are used to build a database. This database is then analyzed by machine learning to construct design charts that are shown to effectively guide the design of the ultra-thin deployable structure. The computational strategy discussed herein is general and can be applied to different problems in structural and materials design, with the potential of finding relevant designs within high-dimensional spaces.https://resolver.caltech.edu/CaltechAUTHORS:20191114-160021163Molecular based temperature and strain rate dependent yield criterion for anisotropic elastomeric thin films
https://resolver.caltech.edu/CaltechAUTHORS:20170818-092431386
Year: 2017
DOI: 10.1016/j.polymer.2017.07.080
A molecular formulation of the onset of plasticity is proposed to assess temperature and strain rate effects in anisotropic semi-crystalline rubbery films. The presented plane stress criterion is based on the strain rate-temperature superposition principle and the cooperative theory of yielding, where some parameters are assumed to be material constants, while others are considered to depend on specific modes of deformation. An orthotropic yield function is developed for a linear low density polyethylene thin film. Uniaxial and biaxial inflation experiments were carried out to determine the yield stress of the membrane via a strain recovery method. It is shown that the 3% offset method predicts the uniaxial elastoplastic transition with good accuracy. Both the tensile yield points along the two principal directions of the film and the biaxial yield stresses are found to obey the superposition principle. The proposed yield criterion is compared against experimental measurements, showing excellent agreement over a wide range of deformation rates and temperatures.https://resolver.caltech.edu/CaltechAUTHORS:20170818-092431386Cure-induced deformation of ultra-thin composite laminates
https://resolver.caltech.edu/CaltechAUTHORS:20190806-133219697
Year: 2018
DOI: 10.2514/6.2018-2241
In fiber reinforced composite materials, the manufacturing process induces residual stresses and distortions that decrease the mechanical performance of the structure and affect its geometry, especially in thin laminates. Multi-physics simulations were performed to assess the spring-in effect in ultra-thin composite parabolic solar reflectors. For this purpose, a resin kinetic model has been developed by means of differential scanning calorimetry experiments. The kinetic relation has been implemented into the finite element software in order to correctly predict the evolution of the composite degree of cure during the manufacturing process. Specimens were produced in an autoclave and their final geometries were measured by means of a non-contact measuring system and compared with numerical predictions, showing very good agreement.https://resolver.caltech.edu/CaltechAUTHORS:20190806-133219697Self-Deployable Joints for Ultra-Light Space Structures
https://resolver.caltech.edu/CaltechAUTHORS:20190805-134838958
Year: 2018
DOI: 10.2514/6.2018-0694
The paper presents ongoing research and development of novel concepts for deployable space structures using self-latching, flexural joints to replace mechanical hinges. The mechanics of deformation of Fiber-Reinforced-Polymers (FRP) joints for in-plane deployment mechanisms are studied. Methods for characterizing these joints via experiments and numerical simulations are proposed. A failure criterion suitable for ultra-thin, plain-weave composites is used to predict failure of the joints and achieve a successful design.https://resolver.caltech.edu/CaltechAUTHORS:20190805-134838958Stress Concentration and Material Failure During Coiling of Ultra-Thin TRAC Booms
https://resolver.caltech.edu/CaltechAUTHORS:20190816-144340271
Year: 2018
DOI: 10.2514/6.2018-0690
Ultra-thin TRAC booms are a promising technology for large deployable structures for space applications. A manufacturing process producing composites TRAC booms with flange thickness as low as 53 μm is proposed. Coiling behavior around hub with radii ranging from 19.1 mm to 31.8 mm is studied both experimentally and through finite element simulations. Due to the thinness of the TRAC boom, a buckle appears in the inner flange, in the transition region from the fully deployed to the coiled configurations. Material failure is observed at this location, and this correlates well with stresses computed in simulation, coupled with the fiber microbuckling failure criterion. Reducing the thickness, either by changing the laminate or by improving the manufacturing process, is shown to reduce stresses, allowing coiling around smaller hubs without material failure.https://resolver.caltech.edu/CaltechAUTHORS:20190816-144340271Ultralight Ladder-type Coilable Space Structures
https://resolver.caltech.edu/CaltechAUTHORS:20190805-134838873
Year: 2018
DOI: 10.2514/6.2018-1200
We describe the concept of an ultralight ladder-type coilable strip used as the main element to build large planar deployable space solar power spacecrafts. It is composed of TRAC longerons connected with lenticular cross-section rods which enables it to fully flatten and thus be packaged efficiently. The design is tackled here as well as the manufacturing of a scaled version of this new type of structures. Finite element analyses are used to understand the underlying behavior of such structures. Experimental model testing is then used as a way of validating this computational framework. Finally a simulation framework enabling simulation at the spacecraft scale is presented and preliminary results obtained with shows how such structures behave while integrated into a larger spacecraft.https://resolver.caltech.edu/CaltechAUTHORS:20190805-134838873A lightweight tile structure integrating photovoltaic conversion and RF power transfer for space solar power applications
https://resolver.caltech.edu/CaltechAUTHORS:20190805-134837271
Year: 2018
DOI: 10.2514/6.2018-2202
We demonstrate the development of a prototype lightweight (1.5 kg/m^3) tile structure capable of photovoltaic solar power capture, conversion to radio frequency power, and transmission through antennas. This modular tile can be repeated over an arbitrary area to forma large aperture which could be placed in orbit to collect sunlight and transmit electricity to any location. Prototype design is described and validated through finite element analysis, and high-precision ultra-light component manufacture and robust assembly are described.https://resolver.caltech.edu/CaltechAUTHORS:20190805-134837271Nonlinear thermomechanical response and constitutive modeling of viscoelastic polyethylene membranes
https://resolver.caltech.edu/CaltechAUTHORS:20171018-094843923
Year: 2018
DOI: 10.1016/j.mechmat.2017.10.004
Thin films of linear low-density polyethylene show a significant time-dependent behavior, strongly reliant on temperature and strain rate effects. A constitutive nonlinear thermo-viscoelastic relation is developed to characterize the response of thin membranes up to yielding, in a wide range of temperatures, strain rates, and mechanical loading conditions. The presented plane stress orthotropic formulation involves the free volume theory of viscoelasticity and the time-temperature superposition principle, necessary to describe non-linearities and non-isothermal conditions. Uniaxial tension tests at constant strain rate and long-duration biaxial inflation experiments have been employed in the calibration of the material parameters. The model has been implemented in the Abaqus finite element code by means of a user-defined subroutine based on a recursive integration algorithm. The accuracy of the constitutive relation has been validated against experimental data of full field diaphragm inflation tests and uniaxial tension, relaxation and cyclic experiments, covering sub-ambient temperatures and strain rate ranges observed during the operation of stratospheric balloons.https://resolver.caltech.edu/CaltechAUTHORS:20171018-094843923Fast and broadband detector for laser radiation
https://resolver.caltech.edu/CaltechAUTHORS:20180615-114153851
Year: 2018
DOI: 10.1117/12.2294002
We developed a fast detector (patent pending) based on the Laser Induced Transverse Voltage (LITV) effect. The advantage of detectors using the LITV effect over pyroelectric sensors and photodiodes for laser radiation measurements is the combination of an overall fast response time, broadband spectral acceptance, high saturation threshold to direct laser irradiation and the possibility to measure pulsed as well as cw-laser sources.
The detector is capable of measuring the energy of single laser pulses with repetition frequencies up to the MHz range, adding the possibility to also measure the output power of cw-lasers.
Moreover, the thermal nature of the sensor enables the capability to work in a broadband spectrum, from UV to THz as well as the possibility of operating in a broad-range (10^(-3)-10^2 W/cm^2 ) of incident average optical power densities of the laser radiation, without the need of adopting optical filters nor other precautions.https://resolver.caltech.edu/CaltechAUTHORS:20180615-114153851Phenomenological model for coupled multi-axial piezoelectricity
https://resolver.caltech.edu/CaltechAUTHORS:20180615-113248296
Year: 2018
DOI: 10.1117/12.2296346
A quantitative calibration of an existing phenomenological model for polycrystalline ferroelectric ceramics is presented. The model relies on remnant strain and polarization as independent variables. Innovative experimental and numerical model identification procedures are developed for the characterization of the coupled electro-mechanical, multi-axial nonlinear constitutive law. Experiments were conducted on thin PZT-5A4E plates subjected to cross-thickness electric field. Unimorph structures with different thickness ratios between PZT-5A4E plate and substrate were tested, to subject the piezo plates to coupled electro-mechanical fields. Material state histories in electric field-strain-polarization space and stress-strain-polarization space were recorded. An optimization procedure is employed for the determination of the model parameters, and the calibrated constitutive law predicts both the uncoupled and coupled experimental observations accurately.https://resolver.caltech.edu/CaltechAUTHORS:20180615-113248296Design of ultra-thin shell structures in the stochastic post-buckling range using Bayesian machine learning and optimization
https://resolver.caltech.edu/CaltechAUTHORS:20180221-091817099
Year: 2018
DOI: 10.1016/j.ijsolstr.2018.01.035
A data-driven computational framework combining Bayesian regression for imperfection-sensitive quantities of interest, uncertainty quantification and multi-objective optimization is developed for the design of complex structures. The framework is used to design ultra-thin carbon fiber deployable shells subjected to two bending conditions. Significant increases in the ultimate buckling loads are shown to be possible, with potential gains on the order of 100% as compared to a previously proposed design. The key to this result is the existence of a large load reserve capability after the initial bifurcation point and well into the post-buckling range that can be effectively explored by the data-driven approach. The computational strategy here presented is general and can be applied to different problems in structural and materials design, with the potential of finding relevant designs within high-dimensional spaces.https://resolver.caltech.edu/CaltechAUTHORS:20180221-091817099Wrinkling of Transversely Loaded Spinning Membranes
https://resolver.caltech.edu/CaltechAUTHORS:20180214-081512136
Year: 2018
DOI: 10.1016/j.ijsolstr.2018.01.031
Spinning membrane structures provide a mass-efficient solution for large space apertures. This paper presents a detailed study of the wrinkling of spinning circular membranes loaded by transverse, uniform loads. Experimental measurements of the angular velocities at which different membranes become wrinkled, and of the wrinkling mode transitions that occur upon spin down of the membrane, are presented. A theoretical formulation of the problem is presented, from which pairs of critical angular velocities and critical transverse loads are determined. A general stability chart is presented, which identifies the stability limits in terms of only two dimensionless parameters, for any membrane. The transition between bending dominated behavior and in-plane dominated behavior is identified, and it is shown that in the bending-dominated case the critical non-dimensional transverse load is independent from the non-dimensional angular velocity.https://resolver.caltech.edu/CaltechAUTHORS:20180214-081512136Shape Measurement of Large Structures in Space: Experiments
https://resolver.caltech.edu/CaltechAUTHORS:20180906-143935251
Year: 2018
DOI: 10.1109/MetroAeroSpace.2018.8453578
A method to reconstruct the shape of a large planar structure in space is introduced and demonstrated through a lab-scale experiment. Lightweight sun sensors are distributed on the structure to measure local angles relative to the sun. The methodology to integrate the measured angles into the shape of the structure, based on a decomposition of the shape into basis functions is introduced. This methodology has been implemented on a lab-scale experiment. The design of the sensors is based on a 4 pixel pinhole camera. The calibration method for these sensors is presented as well as the techniques to integrate and communicate with them. A 1.2 m by 20 cm structure was designed and populated with sensors to show the performance of an integrated system. Preliminary results show an accuracy of 1 mm RMS on the shape reconstruction of this structure.https://resolver.caltech.edu/CaltechAUTHORS:20180906-143935251Ultralight Energy Converter Tile for the Space Solar Power Initiative
https://resolver.caltech.edu/CaltechAUTHORS:20181210-140402265
Year: 2018
DOI: 10.1109/pvsc.2018.8547403
We have fabricated a functional prototype of an ultralight power converter tile; a modular building block for a space-based solar power system. The tile is ∼10×15 cm in area, and weighs ∼1.5 kg/m^2. It comprises a photovoltaic (PV) solar energy collector, a radio-frequency (RF) power converter, and an array of transmission antennas. The PV collector subassembly utilizes ∼15x, 1D parabolic trough reflective concentrators with triple-junction (3J) solar cells. It has areal mass of ∼0.8 kg/m^2, 74% optical efficiency, and a peak specific power of ∼230W/kg. We demonstrated wireless power transmission over a distance of ∼50 cm in our lab. Analysis of the sources of mass and inefficiency suggest a path towards achieving dramatically higher performance with future designs.https://resolver.caltech.edu/CaltechAUTHORS:20181210-140402265Design of Structures With Multiple Equilibrium Configurations
https://resolver.caltech.edu/CaltechAUTHORS:20190404-081554007
Year: 2018
DOI: 10.1115/DETC2018-86157
Being able to design structures with multiple equilibrium configurations is the basis for the design of multi-stable structures, which are of interest for future research on multi-configuration structures that require 'simple' actuation schemes. It is already known that adding elastic springs to a rigid mechanism can create structures with multiple equilibrium configurations. The spring properties, such as their rest positions, can be taken as design parameters that can be used to achieve specific equilibrium configurations of the structure. This paper provides a linearized formulation for the equilibrium constraints that can be solved for the rest positions of the springs. This method allows the design of specific equilibrium configurations. It can also handle more complex problems and is easier to solve in comparison to existent techniques. An example design of a four-bar linkage that has 5 equilibrium configurations is presented.https://resolver.caltech.edu/CaltechAUTHORS:20190404-081554007Nonlinear vibration of transversely-loaded spinning membranes
https://resolver.caltech.edu/CaltechAUTHORS:20180502-090136585
Year: 2018
DOI: 10.1016/j.jsv.2018.04.015
The paper studies the transverse nonlinear vibration of an isotropic and homogeneous annular membrane spinning at constant angular velocity, under the action of a uniform transverse load. The equilibrium configuration of the membrane, clamped along the inner edge and free along the outer edge, and the natural frequencies of vibration of the membrane are calculated. A Galerkin procedure is used to determine a reduced order model describing the weakly nonlinear vibration of the membrane, and it is shown that near-resonance vibration can be modeled as a single degree of freedom Helmholtz-Duffing oscillator. A detailed study at vibration frequencies close to the fundamental, axisymmetric vibration mode shows a transition from softening to hardening behavior, and jump phenomena or hysteretic behavior depending on the angular velocity, the transverse load, the amplitude of dynamic excitation and the damping ratio. The results are in agreement with dynamic implicit finite element simulations in Abaqus/Standard and direct experimental measurements.https://resolver.caltech.edu/CaltechAUTHORS:20180502-090136585Searching for Imperfection Insensitive Externally Pressurized Near-Spherical Thin Shells
https://resolver.caltech.edu/CaltechAUTHORS:20180615-091650052
Year: 2018
DOI: 10.1016/j.jmps.2018.06.008
This paper studies the buckling behavior and imperfection sensitivity of geodesic and stellated shells subject to external pressure. It is shown that these structures can completely eliminate the severe imperfection sensitivity of spherical shells and can achieve buckling pressure and mass efficiency higher than the perfect sphere. Key results of this paper are as follows. First, a shell with the shape of an icosahedron can carry external pressure significantly higher than a spherical shell, when the effects of geometric imperfections are considered. Second, stellated shells are generally insensitive to imperfections. For pyramids with height-to-radius ratios greater than 35% the buckling pressure is greater than for a perfect sphere. The specific ratio 45% gives the highest buckling pressure, 28% higher than the perfect sphere. Third, stellated icosahedra with concave pyramids have higher mass efficiency than the perfect sphere. Fourth, in terms of volume efficiency, geodesic shells are comparable to spherical shells with a knockdown factor of 0.2 and convex stellated shells are comparable to spherical shells with a knockdown factor of 0.65.https://resolver.caltech.edu/CaltechAUTHORS:20180615-091650052Attitude maneuver design for planar space solar power satellites
https://resolver.caltech.edu/CaltechAUTHORS:20191205-093402644
Year: 2019
This paper investigates the attitude dynamics of a planar space solar power satellite (SSPS) by formulating the power-optimal guidance problem as a nonlinear trajectory optimization problem. The power-optimal guidance problem determines the orientation of an SSPS throughout its orbit that maximizes the amount of power transmitted to Earth. This transmitted power is a function of the relative geometry between the SSPS, the Sun, and the receiving station. Hence, it is inherently coupled to the attitude of the SSPS, i.e., the orientation that maximizes power transmission changes as the relative geometry changes. We first approximate the discretized trajectory optimization problem as a quadratic program (QP). We then solve the QP to obtain attitude trajectory designs for various orbits. These solutions highlight how maximizing transmitted power typically requires large slew maneuvers. Ultimately, by quantifying control and propellant requirements for various orbits, we emphasize how maneuver dynamics play an important role in SSPS design.https://resolver.caltech.edu/CaltechAUTHORS:20191205-093402644Topology Optimization of Composite Self-Deployable Thin Shells with Cutouts
https://resolver.caltech.edu/CaltechAUTHORS:20210913-222227787
Year: 2019
DOI: 10.2514/6.2019-1524
The paper presents topology optimization studies of selfs-deployable joints in thin-walled tubular structures. The joints are made entirely of ultra-thin, fiber reinforced composite materials. The objective of this research is to strategically position cutouts on the joints so that they can fold without failing, while maximizing the deployed bending stiffness. The optimal shape and position of cutouts are the results of concurrent topology optimization of these composite, thin-shell joints with geometrical non-linearities, due to their folding and self-deployable nature. Numerical methods to accurately detect failure are implemented and results from a novel level-set method for topology optimization are compared to results from classical parametric optimization and preliminary designs based on physical intuition.https://resolver.caltech.edu/CaltechAUTHORS:20210913-222227787Large-Area Deployable Reflectarray Antenna for CubeSats
https://resolver.caltech.edu/CaltechAUTHORS:20191112-154118926
Year: 2019
DOI: 10.2514/6.2019-2257
Herein is described a 1.5 m x 1.5 m reflectarray antenna designed to stow in a cylinder of 20 cm diameter and 9 cm height, and then be unfolded to provide an aperture suitable for radio frequency (RF) operations at X-band (8.4 GHz) and produce 39.6 dB of gain. The mass of the reflectarray, as measured for a full-scale prototype, is 1.75 kg. The reflectarray comprises a number of crossed-dipoles held 5 mm above a ground plane. The dipole layer and the ground plane are supported by thin planar composite facesheets; the separation between these facesheets is provided by thin composite collapsible 'S'-shaped-springs. The structure is divided into a number of quartz-epoxy composite strips arranged in concentric squares and connected to each other using slipping folds. The strips can be flattened, star-folded, and wrapped to package within the compact cylindrical volume. A full-scale prototype of this reflectarray was constructed and tested. Stowage in the design volume was successfully demonstrated, and all RF performance requirements were met, as shown by a pre-stowage RF test and a post-stowage RF test.https://resolver.caltech.edu/CaltechAUTHORS:20191112-154118926Parametric Design of Conforming Joints for Thin-Shell Coilable Structures
https://resolver.caltech.edu/CaltechAUTHORS:20190805-134838792
Year: 2019
DOI: 10.2514/6.2019-1259
This paper addresses the problem of designing and building structural connections (joints) for ultra-thin shells employed in large coilable structures for space applications. A conforming joint design concept for ladder-type coilable thin shells is proposed. A parametric design tool was developed to study the geometry of two joints that become overlapped in the coiled configuration as a function of the coiling radius and joint radii. Parametric design results are validated through finite element simulations. The proposed design tool provides a high level of design flexibility and is of interest in the spacecraft design process making use of ultra-thin shells.https://resolver.caltech.edu/CaltechAUTHORS:20190805-134838792Reducing Stress Concentration in the Transition Region of Coilable Ultra-Thin-Shell Booms
https://resolver.caltech.edu/CaltechAUTHORS:20190805-134838677
Year: 2019
DOI: 10.2514/6.2019-1522
High stress concentrations leading to material failure have been observed in TRAC booms coiled under tension around a circular hub. The stress concentrations are typically observed in the transition region between the fully deployed and coiled sections of the boom. A numerical simulation framework is proposed to model the coiling process analyses the stress distribution in the transition region. Isotropic booms are first studied to understand the effects of the cross-section geometry and the boundary conditions during coiling. Compressive stress is reduced by 13% and 26% by using a variable curvature cross-section and adding nip rollers in the coiling mechanism respectively. For an ultra-thin glass fiber-carbon fiber composite laminate, the compressive stress is similarly reduced by 24% and 11%. The variable curvature cross-section is shown to eliminate the stress concentration in the transition region.https://resolver.caltech.edu/CaltechAUTHORS:20190805-134838677Ultralight Spacecraft Structure Prototype
https://resolver.caltech.edu/CaltechAUTHORS:20190805-134837694
Year: 2019
DOI: 10.2514/6.2019-1749
We demonstrate the development of a lightweight 1.7 m X 1.7 m prototype spacecraft structure with areal density of 150 g/m^2. The structure is composed of individual ladder-type components that can be used to support flexible multi0-functional elements such as integrated power collection and wireless transmission tiles used for space solar power. This spacecraft structure design is scalable up to 60 m X 60 m. The structural design, ultra-light component manufacture and, prototype assembly are demonstrated. Shape accuracy within 0.5° from nominal is achieved and outlook for further mass reduction is described.https://resolver.caltech.edu/CaltechAUTHORS:20190805-134837694Stability Analysis of Coiled Tape Springs
https://resolver.caltech.edu/CaltechAUTHORS:20190805-134838114
Year: 2019
DOI: 10.2514/6.2019-1523
Tape springs have been used for many years in deployable booms and space mechanisms and currently are bing considered as components for more advanced deployable structures. Tape springs can be elastically coiled and will self-deploy when released. Their stability in the packaged configuration is critical for these applications. We propose a numerical and analytical framework to investigate the stability of coiled isotropic tape springs, where neither tension nor radial pressure are applied. Torsional and bending instabilities were observed when the ration between the coiled radius and the radius of the cross-section exceeded a critical value. A stability boundary is derived for different geometries and material properties. The effects of varying the number of coils and the self-contact conditions between adjacent loops of a tape spring are also studied, and the existence of out-of-plane instability modes is discussed.https://resolver.caltech.edu/CaltechAUTHORS:20190805-134838114Closed Cross-Section Dual-Matrix Composite Hinge for Deployable Structures
https://resolver.caltech.edu/CaltechAUTHORS:20181022-154930890
Year: 2019
DOI: 10.1016/j.compstruct.2018.10.040
Dual-matrix composite structures with localized elastomer composite hinges have been proposed to enable packaging with much smaller fold radii than allowed by traditional resin-based fiber reinforced composites. Previous studies have been limited to proof-of-concept of folding capabilities and constitutive modeling of elastomer composites. A novel closed cross-section dual-matrix deployable hinge is studied here to develop the tools for studying the deployment of general dual-matrix structures. A set of tools for the analysis of deployment of this simple structure is developed: an analytic model that minimizes the strain energy in the folded configuration, experimental characterization, and finite element techniques using the LS-Dyna commercial software. The three models are used to predict the packaged shape and deployment moments, and are shown to be in good agreement amongst themselves. The analytic model is used to demonstrate control of the folded shape of the hinge using the stiffness of the elastomer composite. This behavior is verified using finite element models developed in the LS-Dyna commercial code. The simulations are used to predict the localized fold radius of the hinge within 3% and deployment moments within 5% by accounting for the microbuckled stiffness of the elastomer composite.https://resolver.caltech.edu/CaltechAUTHORS:20181022-154930890Small Satellites: A Revolution in Space Science
https://resolver.caltech.edu/CaltechAUTHORS:20190213-133819234
Year: 2019
DOI: 10.26206/YH3H-ZA97
This report describes the results of a study program sponsored by the Keck Institute
for Space Studies (KISS) at the California Institute of Technology to explore how small
satellite systems can uniquely enable new discoveries in space science. The
disciplines studied span astrophysics, heliophysics, and planetary science (including
NEOs, and other small bodies) based on remote and in-situ observations. The two
workshops and study period that comprised this program brought together space
scientists, engineers, technologists, mission designers, and program managers over 9
months. This invitation-only study program included plenary and subject matter
working groups, as well as short courses and lectures for the public. Our goal was to
conceive novel scientific observations, while identifying technical roadblocks, with the
vision of advancing a new era of unique explorations in space science achievable
using small satellite platforms from 200 kg down to the sub-kg level.
The study program participants focused on the role of small satellites to advance
space science at all levels from observational techniques through mission concept
design. Although the primary goal was to conceive mission concepts that may require
significant technology advances, a number of concepts realizable in the near-term
were also identified. In this way, one unexpected outcome of the study program
established the groundwork for the next revolution in space science, driven by small
satellites platforms, with a near-term and far-term focus.
There were a total of 35 KISS study participants across both workshops (July 16-20,
2012 and October 29-31, 2012) from 15 institutions including JPL, Caltech, JA /
PocketSpacecraft.com, MIT, UCLA, U. Texas at Austin, U. Michigan, USC, The
Planetary Society, Space Telescope Science Institute, Cornell, Cal Poly SLO, Johns
Hopkins University, NRL, and Tyvak LLC. The first workshop focused on identifying
new mission concepts while the second workshop explored the technology and
engineering challenges identified via a facilitated mission concept concurrent design
exercise. The Keck Institute limits the number of participants per workshop to at most
30 to encourage close interaction where roughly 20% involved in this study were
students.
This report is organized to communicate the outcome of the study program. It is also
meant to serve as a public document to inform the larger community of the role small
satellites can have to initiate a new program of exploration and discovery in space
science. As such, it includes recommendations that could inform programmatic
1-5
decision making within space exploration agencies, both in the USA and
internationally, on the promise of low-cost, focused, and high impact science should a
strategic plan for small satellite space science be pursued. As such, the study
program organizers and all participants are available to respond to any aspect of this
report.https://resolver.caltech.edu/CaltechAUTHORS:20190213-133819234A flexible phased array system with low areal mass density
https://resolver.caltech.edu/CaltechAUTHORS:20190416-120325923
Year: 2019
DOI: 10.1038/s41928-019-0247-9
Phased arrays are multiple antenna systems capable of forming and steering beams electronically using constructive and destructive interference between sources. They are employed extensively in radar and communication systems but are typically rigid, bulky and heavy, which limits their use in compact or portable devices and systems. Here, we report a scalable phased array system that is both lightweight and flexible. The array architecture consists of a self-monitoring complementary metal–oxide–semiconductor-based integrated circuit, which is responsible for generating multiple independent phase- and amplitude-controlled signal channels, combined with flexible and collapsible radiating structures. The modular platform, which can be collapsed, rolled and folded, is capable of operating standalone or as a subarray in a larger-scale flexible phased array system. To illustrate the capabilities of the approach, we created a 4 × 4 flexible phased array tile operating at 9.4–10.4 GHz, with a low areal mass density of 0.1 g cm^(−2). We also created a flexible phased array prototype that is powered by photovoltaic cells and intended for use in a wireless space-based solar power transfer array.https://resolver.caltech.edu/CaltechAUTHORS:20190416-120325923Shear-induced buckling of a thin elastic disk undergoing spin-up
https://resolver.caltech.edu/CaltechAUTHORS:20190208-125359102
Year: 2019
DOI: 10.1016/j.ijsolstr.2019.01.038
The stability of a spinning thin elastic disk has been widely studied due to its central importance in engineering. While the plastic deformation and failure of an annular disk mounted on a rigid and accelerating circular shaft are well understood, shear-induced elastic buckling of the disk due to this 'spin-up' is yet to be reported. Here, we calculate this buckling behavior within the framework of the Föppl–von Kármán equations and give numerical results as a function of the disk's aspect ratio (inner-to-outer radius) and Poisson's ratio. This shows that shear-induced elastic buckling can dominate plastic failure in many cases of practical interest. When combined with existing theory for plastic failure, the results of the present study provide foundation results for a multitude of applications including the characterization of accelerating compact disks and deployment of space sails by centrifugal forces.https://resolver.caltech.edu/CaltechAUTHORS:20190208-125359102Sequentially Controlled Dynamic Deployment of Ultra-Thin Shell Structures
https://resolver.caltech.edu/CaltechAUTHORS:20200113-075647741
Year: 2020
DOI: 10.2514/6.2020-0690
This paper presents an approach to achieve the staged deployment of planar structures composed of multiple thin-shell elements. Releasable constraints are used to prescribe intermediate, known configurations along a strain energy-driven deployment path. An analytical model is derived to design the nominal deployment sequence of the structure by identifying kinematically compatible paths. Then, a finite element model is developed to capture the dynamic behavior of the shells during a staged deployment. Practical considerations, such as the deployment envelope and incorporation of the structure in a deployment mechanism are discussed. Finally, the proposed deployment sequence is demonstrated experimentally.https://resolver.caltech.edu/CaltechAUTHORS:20200113-075647741Interface Failure Analysis of Triangular Rollable and Collapsible (TRAC) Booms
https://resolver.caltech.edu/CaltechAUTHORS:20200113-081226991
Year: 2020
DOI: 10.2514/6.2020-0694
Characterizing the interface bond of thin-ply composites is important for assessing the overall structural integrity. Due to the flexibility of thin composite laminates, it is not feasible to carry out mode I double cantilever beam (DCB) and mode II end notch flexure (ENF) tests, due to the large geometric changes undergone during testing. To reduce the compliance during testing, thick aluminum substrates are bonded to the two free-surfaces of the test laminates. DCB and ENF tests are specifically carried out in this configuration. A specific glass fiber plain weave interface of a 7-ply composite structure is tested. µCT imaging shows the presence of periodic voids of size scales of 200 µm, and local delaminated regions of 0 . 7 − 5 . 6 mm. The former is attributed to capillary effects from the glass tows, while the latter is due to insufficient resin flow during the two-cure manufacturing process.https://resolver.caltech.edu/CaltechAUTHORS:20200113-081226991Experimental Study of Time-dependent Failure of High Strain Composites
https://resolver.caltech.edu/CaltechAUTHORS:20200110-160834737
Year: 2020
DOI: 10.2514/6.2020-0207
High strain composites for coilable space structures can undergo micro-structural changes in the time period between stowage and deployment. These changes include the accumulation of residual stresses in response to curvature changes (stress-relaxation) and accumulation of damage, which may lead to rupture of high strain composites. Currently, the mechanisms that cause damage growth and failure are not well understood. In this study, new experimental approaches are explored for applying constant curvature changes, that replicate the stowage conditions while imaging the evaluation of cracks on the compression surface and of damage in the micro-structure of the test sample. The test temperature is raised to accelerate the failure process.https://resolver.caltech.edu/CaltechAUTHORS:20200110-160834737Buckling of Ultralight Ladder-type Coilable Space Structures
https://resolver.caltech.edu/CaltechAUTHORS:20200113-083856811
Year: 2020
DOI: 10.2514/6.2020-1437
We analyse the buckling and post-buckling behavior of ultralight ladder-type coilable structures for space solar power applications. The structures are composed of thin-shell longitudinal elements connected by thin rods, which can be flattened and packaged efficiently. Rather than relying on an eigenvalue based analysis, this paper presents an alternative approach to thin-shell buckling based on recent work on the stability of cylindrical and spherical shells. The stability of ladder-type structures loaded by normal pressure is studied using a probe that locally displaces the structure and a stability landscape for the structure is plotted. This landscape plot gives insight into the structure's buckling, post-buckling, and sensitivity to disturbances.https://resolver.caltech.edu/CaltechAUTHORS:20200113-083856811Ultralight Deployable Space Structure Prototype
https://resolver.caltech.edu/CaltechAUTHORS:20200113-080052698
Year: 2020
DOI: 10.2514/6.2020-0692
We present a lab demonstration of the packaging and deployment of an ultralight space structure prototype composed of thin shell longerons and battens. The prototype is integrated with a thin polyimide membrane which serves as mass representative of multi-functional elements that could be integrated into this type of deployable, such as integrated power collection and wireless transmission tiles for space solar power. A deployment mechanism using actively controlled pressure to package and deploy this structure ensuring its integrity is described. The deployable structure and deployment mechanism designs are scalable to 60 m X 60 m structures. The structure's mass scaling to larger sizes is described.https://resolver.caltech.edu/CaltechAUTHORS:20200113-080052698A Theory for the Design of Multi-Stable Morphing Structures
https://resolver.caltech.edu/CaltechAUTHORS:20191025-133026102
Year: 2020
DOI: 10.1016/j.jmps.2019.103772
Multi-stable structures can provide desired reconfigurability and require relatively simple actuation. This paper considers general bar and plate structures connected by frictionless hinges that are to be made locally stable in a set of chosen target configurations by attaching extensional and rotational, linear-elastic springs to the structure. The unstressed lengths and angles of the springs, as well as their stiffnesses, are the unknown design parameters to be determined. A set of equilibrium and stability conditions to be satisfied in each of the target configurations of the structure are derived. Solutions of these equations provide specific values of the spring properties that correspond to local energy minima in all of the target configurations. The formulation is fully general and is applicable to structures of any complexity. A simple example is used to illustrate the design process for a bi-stable origami structure and a physical prototype is also presented.https://resolver.caltech.edu/CaltechAUTHORS:20191025-133026102Power-Optimal Guidance for Planar Space Solar Power Satellites
https://resolver.caltech.edu/CaltechAUTHORS:20191224-093207317
Year: 2020
DOI: 10.2514/1.g004643
This paper presents power-optimal guidance for a planar space solar power satellite (SSPS). Power-optimal guidance is the attitude trajectory that maximizes the solar power transmitted by the SSPS. Planarity is important because it couples the orientations of the SSPS's photovoltaic and antenna surfaces. Hence, the transmitted power depends on the relative geometry between the SSPS, the sun, and the receiving station. The orientation that maximizes power transfer changes as this relative geometry changes. Both single- and dual-sided SSPS architectures are considered. A single-sided SSPS has one photovoltaic surface and one antenna surface. A dual-sided SSPS is a single-sided SSPS with at least one additional photovoltaic or antenna surface. Geometric arguments show that a dual-sided SSPS has superior performance to a single-sided SSPS. Power-optimal guidance is then presented for the special cases of SSPSs in geostationary Earth orbit, medium Earth orbit, and low Earth orbit transmitting to an equatorial receiving station at the time of Earth's vernal equinox. These examples emphasize important solution properties, including the need for large slew maneuvers, and they show that, even though system efficiency decreases as orbit altitude decreases, reduced path losses actually increase the amount of received energy per unit aperture area. This has significant system implications for future space solar power missions.https://resolver.caltech.edu/CaltechAUTHORS:20191224-093207317Forms and Concepts for Lightweight Structures
https://resolver.caltech.edu/CaltechAUTHORS:20210729-223659014
Year: 2020
DOI: 10.1017/9781139048569
[no abstract]https://resolver.caltech.edu/CaltechAUTHORS:20210729-223659014Tension-Stabilized Coiling of Isotropic Tape Springs
https://resolver.caltech.edu/CaltechAUTHORS:20190924-095350723
Year: 2020
DOI: 10.1016/j.ijsolstr.2019.09.010
A tape spring can be held tightly coiled on a circular cylinder by means of a tension force applied at the tip. This paper determines the smallest value of the required tension force by means of analytical methods, experiments and detailed numerical simulations. The minimum force depends on the coiling ratio, defined as the ratio between the transverse radius of the tape spring and the radius of the cylinder. It varies with an inverse quadratic relation for coiling ratios smaller than 1 (bending-dominated regime) and with a linear relation for coiling ratios greater than 3.424 (tension-dominated regime). For coiling ratios between 1 and 3.424 there is an intermediate behavior, and the required tension force is non-unique and rather small.https://resolver.caltech.edu/CaltechAUTHORS:20190924-095350723An Ultralight Concentrator Photovoltaic System for Space Solar Power Harvesting
https://resolver.caltech.edu/CaltechAUTHORS:20200128-142200161
Year: 2020
DOI: 10.1016/j.actaastro.2019.12.032
We present a detailed design treatment for a concentrating photovoltaic mini module subsystem with a specific power of up to 4.1 kW/kg for integration into a space solar power system. Concentrating designs are required to achieve specific power over 1 kW/kg with current high-efficiency III-V multijunction solar cells. The 15 sun, linear concentration concept detailed here reduces the system mass by replacing cell and radiation shield area with ultralight carbon fiber reinforced polymer (CFRP) optics. Reducing the cell size to 1mm width as well as careful optimization of cell architecture and CFRP material and thickness are critical for maintaining cell temperatures under 100 C despite the concentration. We also describe ultralight multilayer optical coatings to increase the thermal emissivity of the concentrator surfaces and enhance radiative transfer for cell cooling, which is a critical technological component of the total system design.https://resolver.caltech.edu/CaltechAUTHORS:20200128-142200161Nonlinear Elastic Buckling of Ultra-Thin Coilable Booms
https://resolver.caltech.edu/CaltechAUTHORS:20200720-095447666
Year: 2020
DOI: 10.1016/j.ijsolstr.2020.06.042
This paper presents a study of the elastic buckling behavior of Triangular Rollable And Collapsible (TRAC) booms under pure bending. An autoclave manufacturing process for ultra-thin composite booms is presented and the behavior of three test samples is investigated experimentally. Two regimes are observed, a pre-buckling regime and a stable post-buckling regime that ends when buckling collapse is reached. The buckling collapse moment, marking the end of the stable post-buckling regime, is typically four times higher than the initial buckling moment. A numerical simulation of the boom behavior with the Abaqus finite element package is presented and all of the features observed experimentally are captured accurately by the simulation, except buckling collapse. The numerical model is also used to study the effect of varying the boom length from 0.3 m to 5.0 m. It is shown that the pre-buckling deformation of the flanges under compression leads to a constant wavelength lateral-torsional buckling mode for which the critical moment is mostly constant across the range of lengths.https://resolver.caltech.edu/CaltechAUTHORS:20200720-095447666Origami-Inspired Shape-Changing Phased Array
https://resolver.caltech.edu/CaltechAUTHORS:20210205-093044804
Year: 2021
DOI: 10.23919/eumc48046.2021.9338189
In situ geometric reconfiguration of a phased array increases the diversity of radiation patterns that can be synthesized by the array. Such shape-changing phased arrays enable new applications by dynamically conforming their shapes to the geometry best suited for a given task. This work presents the design and demonstration of an origami-inspired shape-changing array built out of identical radiating tiles held in place by a mechanical backbone. The array is capable of shifting into planar, spherical, and cylindrical configurations. The benefits of such an array are analyzed by comparing the properties of different geometries and verified with measurements of the first origami-inspired shape-changing phased array.https://resolver.caltech.edu/CaltechAUTHORS:20210205-093044804Propagation of Elastic Folds in the Deployment of Thin Shell Space Structures
https://resolver.caltech.edu/CaltechAUTHORS:20210112-105612128
Year: 2021
DOI: 10.2514/6.2021-0299
This paper investigates the deployment behavior of lightweight flexible space structures consisting of thin shell components. An extensive and detailed study of a symmetrically folded structure that dynamically deploys by releasing its stored elastic energy is presented. The challenges involved with ground testing of this structure are discussed, and a suspension system that allows propagation of the elastic folds is proposed. The dynamics of two 1 m-scale structural prototypes was measured using high-speed Digital Image Correlation. It is shown that, for the tests considered, the elastic folds remain stationary and behave as elastic hinges, resulting in a symmetric and repeatable deployment. Deployment experiments in air and vacuum showed that air mass significantly affects the dynamics of the structure, slowing its deployment by 70 %. However, this effect becomes negligible if the deployable structure is not covered by a film. A finite element model of the deployment is presented. The effects of air are approximated by an added mass to the structure, calculated through simple geometric arguments. This model shows good agreement with experimental results without increasing the associated computational time.https://resolver.caltech.edu/CaltechAUTHORS:20210112-105612128Cable-Stayed Architectures for Large Deployable Spacecraft
https://resolver.caltech.edu/CaltechAUTHORS:20210112-105611630
Year: 2021
DOI: 10.2514/6.2021-1386
Cable-stayed structural architectures, which use a combination of bending and axial load-carrying modes, are potentially more efficient than structural architectures that rely only on bending. However, they are not widely used at present. In this paper, an analytical framework is established to compare the load carrying performance of cable-stayed vs. bending architectures by considering limiting conditions such as global buckling, local shell buckling, material failure, and excessive deflection. For structures of equal span, material properties, mass, and maximum deflection limit, the most efficient cable-stayed geometry is determined and its performance is compared to that of the beam. It is shown that the cable-stayed architecture is more efficient at withstanding external loads and remains optimal over the bending architecture. Design charts for optimal designs of cable-stayed structures for a range of lengths and loads are provided.https://resolver.caltech.edu/CaltechAUTHORS:20210112-105611630Time-efficient geometrically non-linear finite element simulations of thin shell deployable structures
https://resolver.caltech.edu/CaltechAUTHORS:20210112-105611267
Year: 2021
DOI: 10.2514/6.2021-1795
Isogeometric analysis of thin shells can provide higher continuity and exact geometric description. It is shown in the existing literature that isogeometric analysis converges with fewer degrees of freedom than C⁰-continuous finite elements that use Langrange polynomial shape functions, but the speed of the solutions has not been previously assessed. In this research, the geometrically nonlinear bending of a thin shell deployable structure, a tape spring is studied, using both NURBS-based and C⁰-continuous finite elements. The complex deformation of a tape spring makes it a perfect case study to compare the computational efficiency of the mentioned techniques. The simulations are carried out in the commercial software ABAQUS and LS-DYNA, and it is found that isogeometric analysis is at least three times slower than the C⁰-continuous finite element methods.https://resolver.caltech.edu/CaltechAUTHORS:20210112-105611267Deployment Dynamics of Foldable Thin Shell Space Structures
https://resolver.caltech.edu/CaltechAUTHORS:20210514-081314705
Year: 2021
DOI: 10.2514/6.2021-0299
This paper investigates the deployment behavior of lightweight flexible space structures consisting of thin shell components. An extensive and detailed study of a symmetrically folded structure that dynamically deploys by releasing its stored elastic energy is presented. The challenges involved with ground testing of this structure are discussed, and a suspension system that allows propagation of the elastic folds is proposed. The dynamics of two 1 m-scale structural prototypes was measured using high-speed Digital Image Correlation. It is shown that, for the tests considered, the elastic folds remain stationary and behave as elastic hinges, resulting in a symmetric and repeatable deployment. Deployment experiments in air and vacuum showed that air mass significantly affects the dynamics of the structure, slowing its deployment by 70 %. However, this effect becomes negligible if the deployable structure is not covered by a film. A finite element model of the deployment is presented. The effects of air are approximated by an added mass to the structure, calculated through simple geometric arguments. This model shows good agreement with experimental results without increasing the associated computational time.https://resolver.caltech.edu/CaltechAUTHORS:20210514-081314705Reduced-Order Modeling for Flexible Spacecraft Deployment and Dynamics
https://resolver.caltech.edu/CaltechAUTHORS:20210112-105611714
Year: 2021
DOI: 10.2514/6.2021-1385
The present work investigates reduced-order modeling for ultralight, packageable, and self-deployable spacecraft where reduced-order models (ROMs) are required to simulate deployment, structural dynamics during spacecraft maneuvers, and for real-time applications in trajectory optimization and control. In these contexts, ultralight, flexible spacecraft dynamics are characterized by geometrically nonlinear structural deformations combined with large rigid body motions. An approach based on proper orthogonal decomposition (POD), energy-conserving sampling and weighting (ECSW), and a floating frame of reference (FFR) is proposed to construct accurate and efficient ROMs. The proposed approach is then tested on a benchmark problem that involves geometrically nonlinear deformations, large rigid body motions, and strain energy release during dynamic snap-back, the last of which is analogous to the energy release during deployment. The resulting ROM for this benchmark problem is approximately 20% the size of the original full-order model with no appreciable loss of accuracy.https://resolver.caltech.edu/CaltechAUTHORS:20210112-105611714Shape reconstruction of planar flexible spacecraft structures using distributed sun sensors
https://resolver.caltech.edu/CaltechAUTHORS:20210104-164231438
Year: 2021
DOI: 10.1016/j.actaastro.2020.12.056
Flexible planar spacecraft, such as solar sails, phased antenna arrays and space solar power satellites vary their shape in flight and also may not have a known shape after deployment. To allow applications where spacecraft shapes are measured to allow the closed-loop correction of flight or payload parameters, this paper presents a method for measuring shapes with miniature sun sensors embedded within the structure. Two algorithms to reconstruct the shape of the structure from the two local angles to the sun are presented; the first one is geometry-based, whereas the second one uses a finite element model of the structure. Both algorithms are validated on a 1.3 m x 0.25 m structure with 14 novel miniature sun sensors with an accuracy of 5°, developed for the present research. The structure was reconstructed to an accuracy better than one millimeter by both algorithms, after undergoing bending and torsional deformations. While the geometrically based algorithm is fast and accurate for small deformations, the finite element based algorithm performs better overall, especially for larger deformations.https://resolver.caltech.edu/CaltechAUTHORS:20210104-164231438Size effects in plain-weave Astroquartz® deployable thin shells
https://resolver.caltech.edu/CaltechAUTHORS:20210713-174100812
Year: 2021
DOI: 10.1177/0021998320987618
The general scaling trend for brittle materials, in which the strength increases when the sample size decreases, is reversed in plain-weave laminates of Astroquartz® and cyanate ester resin. Specifically, both the shear stiffness and the compressive strength decrease for test samples with widths smaller than 15 times the wavelength of the fabric, and observations at the microscale explain this behavior. The derived scaling is applied to the analysis of a deployable thin shell forming a 90∘ corner hinge with five cutouts on each side. The cutouts leave narrow strips of material with width as small as one fabric wavelength, forming structural ligaments whose strength and stiffness are subject to strong size-scaling effects. A numerical simulation of the folding process followed by a failure analysis is presented, using two alternative material models and failure criteria. The size independent model predicts that the structure will remain damage-free after it is folded and deployed, whereas the size-scaled model predicts that failure will occur. The correctness of the size-scaled model prediction is verified by measuring localized damage in a physical prototype, using x-ray CT scans.https://resolver.caltech.edu/CaltechAUTHORS:20210713-174100812Topology and Shape Optimization of Ultrathin Composite Self-Deployable Shell Structures with Cutouts
https://resolver.caltech.edu/CaltechAUTHORS:20210518-073404833
Year: 2021
DOI: 10.2514/1.j059550
This paper presents two methods to design cutouts that allow damage-free folding of the stiffest possible composite self-deployable thin shell structures of complex shapes. The first method uses level-set functions that define a general number of cutouts. The second method uses a spline representation of the contour of a single cutout and optimizes its shape. Material failure detection is implemented in the solution. Both methods are applied to the design of deployable thin shells forming 90° joints, and multiple viable solutions are obtained. Experiments on the best performing design, a 90–390 μm thick shell made of Astroquartz with a cyanate ester matrix, with five cutouts on each side, are presented to illustrate and validate the proposed approach.https://resolver.caltech.edu/CaltechAUTHORS:20210518-073404833Fully Collapsible Lightweight Dipole Antennas
https://resolver.caltech.edu/CaltechAUTHORS:20220217-686367000
Year: 2021
DOI: 10.1109/aps/ursi47566.2021.9704302
Flexible, deployable phased arrays enable novel and diverse applications but necessitate similarly flexible radiators. Here we present a light and flexible 10GHz dipole antenna, which is co-cured to a glass-fiber composite and suited for flexible phased arrays. The antennas are designed to dynamically conform to new array shapes and be flexible enough to fold completely flat and pop back up upon deployment. We employ a pop-up dipole with a capacitive fingers feed for impedance matching that is highly robust against manufacturing errors. Upon deployment, the antennas exhibit a −10 dB-bandwidth >1.5 GHz and >110° half-power beam width single lobe pattern suitable for beamforming.https://resolver.caltech.edu/CaltechAUTHORS:20220217-686367000Development of the Deployable on-Orbit ultraLight Composite Experiment (DOLCE) for the Space Solar Power Project Demonstration Mission
https://resolver.caltech.edu/CaltechAUTHORS:20220210-928385000
Year: 2022
DOI: 10.2514/6.2022-1266
We describe the development of an engineering model of the DOLCE payload which will demonstrate on orbit for the first time the deployment of an ultralight Caltech SSPP structure. Deployment tests at the subsystem and system levels, launch load analysis and testing, and accelerated aging tests have been conducted. The DOLCE payload will be launched with the SSPD-1 mission which will demonstrate space-based solar power key enabling technologies in photovoltaics, power beaming, and deployable structures.https://resolver.caltech.edu/CaltechAUTHORS:20220210-928385000Propagating Instabilities in Coilable Booms
https://resolver.caltech.edu/CaltechAUTHORS:20220210-928328000
Year: 2022
DOI: 10.2514/6.2022-0407
Coilable booms consisting of thin composite shells bonded along a common edge are being considered for novel deployable spacecraft structures. These booms have many desirable features such as light weight, high stiffness, and high packaging efficiency, but this successful realization poses new challenges. In this paper, we study the propagating buckles that have been observed in the transition region between the coiled and deployed parts of the booms. These buckles, which can cause local stress concentrations and material failure, are typical of booms with built-up sections. They do not occur in tape springs. We investigate the root cause for the propagating buckles and discuss the possibility of limiting the buckle growth by increasing the material shear modulus.https://resolver.caltech.edu/CaltechAUTHORS:20220210-928328000High-Fidelity Simulations of Thin-Shell Deployable Structures with Adaptive Meshing
https://resolver.caltech.edu/CaltechAUTHORS:20220210-928394000
Year: 2022
DOI: 10.2514/6.2022-1269
An adaptive meshing procedure is developed for the analysis of thin shell structures that experience localized elastic deformations associated with the formation of folds. The refinement criterion for remeshing takes into consideration the localization of deformation in the folds, while avoiding excessive refinement outside this region. The local bending strains in two principal directions are used to construct the refinement criterion. A geometrical parameter related to a boundary layer effect is shown to be effective as a limit length for refinement. Isogeometric shell finite elements are used for the simulations. Different tape spring geometries are simulated to illustrate the generality and efficiency of the proposed adaptive procedure.https://resolver.caltech.edu/CaltechAUTHORS:20220210-928394000Launch Vibration of Pre-Tensioned Coiled Structures
https://resolver.caltech.edu/CaltechAUTHORS:20220210-928446000
Year: 2022
DOI: 10.2514/6.2022-1883
Relative movement between slipping layers in a coil due to vibration can cause defects in the structure or damage functional elements, such as photovoltaic cells, attached to the structure. Radial contact pressure between successive layers due to coiling pre-tension provides a frictional force that can be used to resist inter-layer slip. In this study, we propose a stress-field based, analytical friction model to use as a criterion for estimating the frictional shear capacity of a wound roll prior to the onset of slip. Because the radial pressure varies with radial position in the coil, the shear capacity against slippage also varies with position. This analytical shear capacity can then be compared against the shear resultants obtained in finite-element simulations of coiled structures undergoing vibration load. Rather than modeling discrete windings of wound rolls, the starting coiled-stiff assumption is the coil is tensioned sufficiently to behave as a solid. Thus, a finite-element vibration study of a homogenized solid is used to find the loads and locations where shear resultant is larger than the estimated shear capacity, indicating slip. The validity of the coiled-stiff assumption is experimentally verified using a vibration experiment that measures the variation in apparent stiffness of a coiled membrane wound under varying tensions.https://resolver.caltech.edu/CaltechAUTHORS:20220210-928446000Health Monitoring of High Strain Composites Using Embedded Fiber Bragg Grating Sensors
https://resolver.caltech.edu/CaltechAUTHORS:20220210-928413000
Year: 2022
DOI: 10.2514/6.2022-1622
A study on the use of fiber Bragg grating sensors to measure strains in thin-walled composite structures is presented. It includes measurement of the gage factor, or strain conversion coefficient, of small diameter fiber optic sensors. Fiber Bragg grating sensor arrays were embedded into high strain composites and the buildup of strains during manufacturing was tracked. μCT scans of these composites were taken after curing to analyze the micro-structure in the regions surrounding the embedded sensors. Composite laminates with embedded sensors were subjected to a controlled coiling experiment to evaluate the accuracy of the sensors in measuring internal strains.https://resolver.caltech.edu/CaltechAUTHORS:20220210-928413000Lightweight Composite Reflectarray that can be Flattened, Folded, and Coiled for Compact Stowage
https://resolver.caltech.edu/CaltechAUTHORS:20220210-928455000
Year: 2022
DOI: 10.2514/6.2022-1886
Herein is presented a design for a lightweight 5 m x 1 m radio-frequency (RF) reflector that can be flattened, folded, and coiled for compact stowage on board an ESPA-class spacecraft. The reflector is a reflectarray that operates at 3.2 GHz. Compared to state-of-the-art technologies for RF reflectors, the presented design has advantages in terms of areal density, stiffness, deployed stability, and scalability. Thermal and structural analysis is presented to demonstrate deployed stiffness and thermoelastic stability of the proposed design. Thermal analysis is used to predict in-space deployed temperatures in an operational condition, and structural finite element analysis is used to predict deployed vibration modes and frequencies, and the thermoelastic deformation of the deployed reflector. Also presented are the fabrication, assembly, and testing of two one-third-scale-length full-scale-width 1.7 m x 1 m test articles. These test articles are used to experimentally demonstrate RF functioning, stowage, deployment, and RF performance after deployment.https://resolver.caltech.edu/CaltechAUTHORS:20220210-928455000Micromechanics Modeling of Time-dependent Failure of Stowed High-strain Composite Structures
https://resolver.caltech.edu/CaltechAUTHORS:20220210-928345000
Year: 2022
DOI: 10.2514/6.2022-0649
Deployable structures made of thin-ply carbon fiber-reinforced composites are of interest due to their high stiffness to weight ratio, high packaging efficiency, and ability to deploy by the release of stored strain energy. For most applications, the largest strains are applied for the longest time during stowage, and viscoelastic polymers in these fiber-reinforced composites are prone to time-dependent deformation growth and rupture. This paper presents a study of the time-dependent deformation growth and time-dependent failure mechanisms using a micromechanics-based 3D finite element model representation of the composite. The study is focused on a repeating unit cell of a cross-ply carbon fiber laminate consisting of linear-elastic transversely isotropic fibers embedded in a linear viscoelastic matrix. A parametric study of initial fiber misalignment angle and its influence on the deformation growth and time to rupture is presented.https://resolver.caltech.edu/CaltechAUTHORS:20220210-928345000Inextensible Surface Reconstruction Under Small Relative Deformations from Distributed Angle Measurements
https://resolver.caltech.edu/CaltechAUTHORS:20220126-901981200
Year: 2022
DOI: 10.1007/s11263-021-01552-x
A mathematical model to measure the shape of a 3D surface using angle measurements from embedded sensors is presented. The surface is known in a reference configuration and is assumed to have deformed inextensibly to its current shape. An inextensibility condition is enforced through a discretization of the metric tensor generating a finite number of constraints. This model allows to parameterize the shape of the surface using a small number of unknowns which leads to a small number of sensors. We study the singularities of the equations and derive necessary conditions for the problem to be well-posed as well as limitations of the algorithm. Simulations and experiments are performed on developable surfaces under relatively small deformations to analyze the performance of the method and to show the influence of the parameters used in our algorithm. Overall, the proposed method outperforms the current state-of-the-art by almost an order of magnitude.https://resolver.caltech.edu/CaltechAUTHORS:20220126-901981200Probing the Stability of Ladder-Type Coilable Space Structures
https://resolver.caltech.edu/CaltechAUTHORS:20220112-107090239
Year: 2022
DOI: 10.2514/1.j060820
This paper analyzes the buckling and postbuckling behavior of ultralight ladder-type coilable structures, called strips, composed of thin-shell longerons connected by thin rods. Based on recent research on the stability of cylindrical and spherical shells, the stability of strip structures loaded by normal pressure is studied by applying controlled perturbations through localized probing. A plot of these disturbances for increasing pressure is the stability landscape for the structure, which gives insight into the structure's buckling, postbuckling, and sensitivity to disturbances. The probing technique is generalized to higher-order bifurcations along the postbuckling path, and low-energy escape paths into buckling that cannot be predicted by a classical eigenvalue formulation are identified. It is shown that the stability landscape for a pressure-loaded strip is similar to the landscape for classical shells, such as the axially loaded cylinder and the pressure-loaded sphere. Similarly to classical shells, the stability landscape for the strip shows that an early transition into buckling can be triggered by small disturbances; however, while classical shell structures buckle catastrophically, strip structures feature a large stable postbuckling range.https://resolver.caltech.edu/CaltechAUTHORS:20220112-107090239Non-Nuclear Exploration of the Solar System
Study
https://resolver.caltech.edu/CaltechAUTHORS:20220503-222804071
Year: 2022
DOI: 10.7907/h62p-6328
Advances in solar array, electric propulsion (EP), and power beaming technologies will very likely enable future missions to the ice giants (Uranus and Neptune) by spacecraft that are completely solar powered. Between 1959 and 2001 the power from solar arrays on missions in Earth orbit have increased by five orders of magnitude (from 1 W to >100,000 W). Simultaneously, the use of solar power has been extended to ever larger distances from the Sun. Three solar powered missions out to solar ranges of just beyond 5 au have now been developed and flown (Rosetta, Juno, and Lucy). At these distances, the solar insolation is roughly 25 times lower than that at 1 au. Solar-powered spacecraft to Saturn, where the solar insolation is 100 times lower than that at 1 au have recently been proposed to NASA. A solar-powered mission to Uranus would have to function where solar insolation is only 4 times lower than it is at Saturn. For Neptune, it would be 9 times lower than at Saturn.
Three improvements in solar array technology are required to make this feasible. First, solar cells have to be able to function in the low-intensity, low-temperature (LILT) environment at Uranus and Neptune. Specially designed triple-junction solar cells have been tested at JPL under LILT conditions equivalent to the environment at 30 au have shown excellent performance (high efficiency and high fill factor). Second, the size of deployable solar arrays has to increase by one to two orders of magnitude relative to the current state of the art. Third, the areal density of solar arrays has to be reduced by an order of magnitude. This will most likely be accomplished through a combination of new thin-film solar cell technology like the Perovskite cells under development worldwide and the development of new deployable solar array structures such as those under investigation for solar-powered satellites.
The solar insolation at Uranus and Neptune is 400 to 900 times lower, respectively, than it is at 1 au. To provide sufficient power for a spacecraft at these destinations requires very large solar arrays. To be practical, such arrays will necessarily need to be very lightweight with a minimum structure mass. The gentle, low-thrust nature of electric propulsion is a good match for such solar arrays since the continuous acceleration of order 10⁻⁵ g will not drive increases in structure mass. In addition, the availability of large amounts of power provided by these arrays between 1 au and 5 to 10 au enables the design of low-thrust trajectories to the ice giants with attractive flight times. Existing ion propulsion technologies, such as NASA's NEXT ion propulsion system enable flight times of conventionally sized spacecraft (≥1000 kg, not including the solar array) to Uranus of less than 10 years with reasonable propellant masses. For example, a conventionally sized spacecraft with a 150-kg complement of instruments could be delivered to Uranus orbit with a vehicle that has two 60-m x 60-m solar array wings and an areal density of 100 g/m² in a flight time of less than 10 years. The same-sized vehicle could be delivered to orbit around Neptune in a flight time of less than 18 years if the solar array areal density is reduced to 50 g/m². In both cases, larger payload masses can be delivered in similar flight times by increasing the size of the solar array wings. A 440-kg payload mass could be delivered to Neptune orbit in less than 17 years by increasing the solar array size to 70 m x 70 m.
Smaller spacecraft may offer nearer-term opportunities. For example, coupling large, lightweight solar arrays with low-power ion propulsion systems (maximum input power of ~3 kW) can deliver net spacecraft masses to Uranus orbit of several hundred kilograms in flight times of less than 10 years. The only new development for such missions would be solar array wings with dimensions of 30 m x 30 m to 60 m x 60 m with an areal density of 100 g/m². The same EP system could deliver net spacecraft masses of 300 to 500 kg (inclusive of the
payload, but not including the solar array, xenon tank, and xenon mass margin, which are tracked separately) to Neptune orbit with flight times of around 15 years with a 60-m x 60-m solar array that has an areal density of 50 g/m2. Such an array would provide roughly 2.4 kW at Neptune.
The development of directed energy (DE) systems could potentially provide hundreds of watts of power continuously to landed assets from solar-powered orbiting spacecraft. Using a DE system to convert electrical power to light on the orbiting spacecraft and a photo-converter system on the landed asset to convert the DE light back to electricity is effectively a "photonic extension cord." For the DE side, a series of lasers in an array is used to beam power to distant landed assets over distances of hundreds to thousands of kilometers. The landed assets use high efficiency photovoltaics tuned to the laser frequency to convert the laser power back to electrical power. Thermal power from the photon power not converted to electricity may, in some applications, also be useful to the landed asset. State-of-the-art directed-energy systems are solid state, efficient (~50%), low mass (~1 kg/kW_(optical)), and long lifetime (~10⁵ hrs). This technology is improving rapidly, driven by the photonic revolution along with consumer and industrial demand. It is likely even possible to beam power to multiple stationary and even moving targets using unique optical beacons from each target.
The technologies required for non-nuclear exploration of the solar system would also enable or enhance a wide variety of other missions of national interest. The large, ultra-light solar arrays combined with a state-of-the-art electric propulsion system would make possible the orbital exploration of Pluto, as well as a tour of its large moon Charon and smaller moons, with a reasonable mass margin and could potentially eliminate the need for RTGs for this mission. Large, ultra-light solar arrays and state-of-the-art electric propulsion systems could enable missions to chase down and encounter long-period comets and potentially even interstellar objects. This combination of technologies could enable solar electric propulsion (SEP) mission architectures farther out in the solar system, including: a Kuiper belt tour, centaur tour, or maybe even a 'Grand Tour' of the gas and ice giants without need for the most optimal planetary alignment, as with the Voyager missions. Sample returns are the next frontier in planetary exploration. The SEP and solar array technologies discussed here would facilitate sample return from a wide range of bodies, including possibly Ceres, Mars, Enceladus, Titan, Triton, and maybe even Mercury. Beaming power from a large, ultra-light solar array in orbit to a landed asset could enable non-nuclear surface exploration of the ice giant's moons. In the nearer term, directed energy systems could deliver power to the surface of the Moon or Mars. Large, lighter solar arrays could facilitate lower-risk human missions to Mars using very high-power solar electric propulsion systems in mission architectures that don't require rendezvousing with pre-deployed assets for the return trip. Finally, large, ultra-light solar arrays could power an Arecibo-like radar in space, to enhance characterization of potentially hazardous objects. Such high-power solar arrays combined with ion-beam deflection would be greatly enhance the nations's planetary defense capabilities.https://resolver.caltech.edu/CaltechAUTHORS:20220503-222804071Investigation of Equatorial Medium Earth Orbits for Space Solar Power
https://resolver.caltech.edu/CaltechAUTHORS:20211217-98213000
Year: 2022
DOI: 10.1109/taes.2021.3122790
Most existing space solar power concepts place one or more power stations in geosynchronous Earth orbit (GEO). However, due to the limited availability of GEO orbital slots, it may not be feasible to locate a power station in GEO. To overcome this limitation, this article presents a system analysis for a space solar power system that incorporates a constellation of power stations in a 20184 km altitude equatorial medium Earth orbit (MEO). The orbiting power stations are based on the Caltech Space Solar Power Project architecture. The constellation consists of multiple power stations in a shared equatorial MEO each transmitting to a nonequatorial receiving station. The analysis assumes a one-to-one correspondence between the number of power stations and the number of ground stations. Like a GEO-based system, this constellation architecture enables a MEO-based system to provide near continuous power (outside of eclipse) to each ground station. It is shown that a MEO constellation with three or more power stations provides comparable transmission efficiency to a GEO-based system. The levelized cost of electricity (LCOE) is then computed for MEO systems with three, four, and five power stations and compared to the LCOE for the GEO-based system. Ground station area is identified as a significant contributor to the LCOE for the MEO-based systems. The system analysis shows that a MEO constellation with as few as four power stations has an LCOE comparable to GEO, and hence, it is concluded that MEO is a viable alternative to GEO for space solar power.https://resolver.caltech.edu/CaltechAUTHORS:20211217-98213000Deployment Dynamics of Thin-Shell Space Structures
https://resolver.caltech.edu/CaltechAUTHORS:20220204-680152000
Year: 2022
DOI: 10.2514/1.a35172
This study was motivated by the desire to develop accurate simulation models for the deployment dynamics of future, ultralight deployable structures consisting of multiple thin shells packaged elastically, through a combination of folding and coiling. The specific problem studied is the packaging and unconstrained deployment of a rectangular space frame formed by two thin-shell longerons connected by multiple transverse rods, and called a strip. The study included experiments on high-quality test articles, using a suspension system with low inertia and friction. The elastic folds in the strips were tracked with high-speed three-dimensional digital image correlation for deployment in both air and near-vacuum. The study also developed a high-fidelity finite element model of the strips that captures the elastic, localized deformation that occurs during the initial folding, the self-contact between different parts of the structure as the folding develops, and the strain energy stored during the folding process. This model accurately captured the deployment dynamics and self-latching of the strips, as well as the effects of air on deployment.https://resolver.caltech.edu/CaltechAUTHORS:20220204-680152000Mass efficiency of strip-based coilable space structures
https://resolver.caltech.edu/CaltechAUTHORS:20220728-729497000
Year: 2022
DOI: 10.1016/j.ijsolstr.2022.111867
This paper presents a general semi-analytical study of the mass efficiency of coilable plate-like space structures. A bending architecture based on four diagonal booms that support parallel strips is compared to a cable-stayed architecture in which vertical booms and cable stays support the diagonal booms at the tip. Limiting conditions of global buckling, local buckling, material failure, and excessive deflection define the design space for each architecture. Considering pressure loads spanning several orders of magnitude, the optimal areal density of structures of size varying from a few meters to hundreds of meters is determined for both architectures. Design charts for optimal designs are provided for a range of sizes, loads, and deflection limits. It is shown that the cable-stayed architecture is always lighter than the bending architecture, from a few percent to over 30%.https://resolver.caltech.edu/CaltechAUTHORS:20220728-729497000Kirigami tiled surfaces with multiple configurations
https://resolver.caltech.edu/CaltechAUTHORS:20221128-494241100.10
Year: 2022
DOI: 10.1098/rspa.2022.0405
This paper presents new kirigami patterns consisting of tiles connected by sub-folds that can approximate multiple specified target surfaces. The curvature of the surfaces approximated by the tiles varies as the patterns are folded, allowing access to a wide range of curvatures. A numerical framework is developed for the synthesis of the fold patterns that approximate a given set of target surfaces. The pattern synthesis process is framed as a tile placement problem, where compatible tile arrangements associated with each target surface are computed by solving a constrained optimization problem. After computing a set of tile arrangements, sub-folds are added to connect adjacent tiles. The resulting patterns are rigid foldable with many kinematic degrees of freedom, allowing them to achieve configurations that approximate the specified target surfaces. Kinematic simulations verify the existence of continuous paths between the target surfaces. A prototype pattern with six target surfaces is fabricated using three-dimensional printed components.https://resolver.caltech.edu/CaltechAUTHORS:20221128-494241100.10Probing the stability of thin-shell space structures under bending
https://resolver.caltech.edu/CaltechAUTHORS:20220706-534199000
Year: 2022
DOI: 10.1016/j.ijsolstr.2022.111806
The stability of lightweight space structures composed of longitudinal thin-shell elements connected transversely by thin rods is investigated, extending recent work on the stability of cylindrical and spherical shells. The role of localization in the buckling of these structures is investigated and early transitions into the post-buckling regime are unveiled using a probe that locally displaces the structure. Multiple probe locations are studied and the probe force versus probe displacement curves are analyzed and plotted to assess the structure's stability. The probing method enables the computation of the energy input needed to transition early into a post-buckling state, which is central to determining the critical buckling mechanism for the structure. A stability landscape is finally plotted for the critical buckling mechanism. It gives insight into the post-buckling stability of the structure and the existence of localized post-buckling states in the close vicinity of the fundamental equilibrium path.https://resolver.caltech.edu/CaltechAUTHORS:20220706-534199000Formation and propagation of buckles in coilable cylindrical thin shells with a thickness discontinuity
https://resolver.caltech.edu/CaltechAUTHORS:20221209-478595000.2
Year: 2022
DOI: 10.1016/j.ijsolstr.2022.112010
This paper studies the snap-through buckling that occurs ahead of the coiled region in thin, linear-elastic, isotropic coilable cylindrical shells with a sudden change in the thickness of the shell cross section. The study is focused on Triangular Rollable And Collapsible (TRAC) booms. It is shown that coiling of these shells leads to longitudinal compression of the inner flange mid-surface, which in turn leads to the formation of a buckle in the transition region between the fully coiled and fully deployed parts of the inner flange. This buckle grows to reach a steady-state configuration and is then pushed along the shell without changing its shape when the shell is coiled.https://resolver.caltech.edu/CaltechAUTHORS:20221209-478595000.2Modeling of Damage in Coilable Composite Shell Structures
https://resolver.caltech.edu/CaltechAUTHORS:20230327-902890000.24
Year: 2023
DOI: 10.2514/6.2023-0364
Coilable composite shell structures, composed of ultra-thin laminates, are ideal for deployable space structures applications. Their ability to be flattened and coiled for packaging, and deployed in their operational configuration makes them suitable for many space missions. Due to the complex states of stresses that occur in a composite shell during these processes (coiling, stowage, and deployment), material failure may be induced. This in turn would negatively affect the deployment, cause shape distortions, reduce the stiffness of the shell, or even lead to catastrophic failure of the mission. Therefore, predicting the failure modes and mechanisms of ultra-thin laminates at the structural scale is critical for design and certification purposes. However, this is often complicated by the complex microstructure and the multiple length-scales (micro and meso) associated with composites. This study presents a finite element model with progressive damage that effectively captures the ply failure modes. This is done through a damage constitutive model, where local cracks in the shell are smeared within a finite element. The fracture properties of interest are experimentally measured and incorporated into the model. The salient features of the model needed to capture failure are identified by comparing the simulation results with experiments. This is achieved by analyzing the coiling of a TRAC longeron shell structure.https://resolver.caltech.edu/CaltechAUTHORS:20230327-902890000.24Nonlinear Behavior of IM7 Carbon Fibers in Compression Leads to Bending Nonlinearity of High-Strain Composites
https://resolver.caltech.edu/CaltechAUTHORS:20230327-902858000.18
Year: 2023
DOI: 10.2514/6.2023-0580
This paper presents an experimental characterization of carbon fibers under compression and the influence of their nonlinear behavior on the bending nonlinearity of high-strain composites (HSC). The study is focused on HexTow IM7, a pan-based carbon fiber compressed under in-situ scanning electron microscopic (SEM) imaging. The sample preparation and experimental procedure of both single fiber direct compression tests and column bending tests of HSC samples are presented. Nonlinearity at the individual fiber level could not be observed due to the limitations of the load cell in the single fiber direct compression experiment. Using the column bending tests, a shift in the neutral axis due to the nonlinear compression behavior of fibers is observed.https://resolver.caltech.edu/CaltechAUTHORS:20230327-902858000.18Slew Maneuver Constraints for Agile Flexible Spacecraft
https://resolver.caltech.edu/CaltechAUTHORS:20230327-902813000.11
Year: 2023
DOI: 10.2514/6.2023-1883
Traditional spacecraft design paradigms rely on stiff bus structures with comparatively flexible appendages. More recent trends, however, trade deployed stiffness for packaging efficiency to stow apertures with larger areas inside existing launch vehicles. By leveraging recent advances in materials and structures, these spacecraft may be up to several orders of magnitude lighter and more flexible than the current state-of-the-art. Motivated by the goal of achieving agility despite structural flexibility, this paper proposes a quantitative method for determining structure-based performance limits for maneuvering flexible spacecraft. It then uses a geometrically nonlinear flexible multibody dynamics model of a representative very flexible spacecraft to verify this method. The results demonstrate that, contrary to common assumptions, other constraints impose more restrictive limits on maneuverability than the dynamics of the structure. In particular, it is shown that the available attitude control system momentum and torque are often significantly more limiting than the compliance of the structure. Consequently, these results suggest that there is an opportunity to design less-conservative, higher-performance space systems that can either be maneuvered faster, assuming suitable actuators are available, or built using lighter-weight, less-stiff architectures that move the structure-based performance limits closer to those of the rest of the system.https://resolver.caltech.edu/CaltechAUTHORS:20230327-902813000.11Launch Vibration Damping Using Slip in Pretensioned Coils
https://resolver.caltech.edu/CaltechAUTHORS:20230327-902798000.8
Year: 2023
DOI: 10.2514/6.2023-2066
Vibration management is important for the survivability of structures during launch, and is particularly challenging for large deployable space structures. Adding damping to a structure reduces the overall level of response excitation, which increases survivability. Structural damping occurs through the dissipation of energy during vibration. One such energy dissipation mechanism that can be utilized to increase damping is friction, such as the friction between slipping layers of a wound roll. In this paper, we study the vibration response of a structure, which has a pre-tensioned coil wound around it. Here, the damping is provided by friction between slipping layers in the pre-tensioned coil. An experiment is performed on a small-scale setup to evaluate the feasibility of this approach by measuring the frequency response and damping under different winding tensions. The same setup is used to measure layer slip during vibration, using a high speed camera and tracking targets to identify the regions with the largest slip, indicating higher contribution to energy dissipation. To confirm understanding of the damping mechanism, a 3D finite-element simulation is created in an attempt to capture the variation in frequency response and locations of slip with winding tension measured experimentally.https://resolver.caltech.edu/CaltechAUTHORS:20230327-902798000.8Buckling Analysis of a Ladder Deployable Structure Supporting a Prestressed Film
https://resolver.caltech.edu/CaltechAUTHORS:20230327-902885000.22
Year: 2023
DOI: 10.2514/6.2023-0366
Controlling the deflection and distortion of lightweight space structures is crucial for their function in space. In this paper, we consider the distortion of a ladder structure when being connected to a film using prestressed kirigami springs. The ladder structure is made with longitudinal CFRP Triangular Rollable and Collapsible (TRAC) booms braced by battens in the transverse direction due to prestress. This paper shows that the distortion is the result of the global buckling of the ladder structure. Then, the design space of the ladder structure has been explored to study the effects of design variables on the magnitude of shape distortion.https://resolver.caltech.edu/CaltechAUTHORS:20230327-902885000.22Strain Measurement in Coilable Thin Composite Shells with Embedded Fiber Bragg Grating Sensors
https://resolver.caltech.edu/CaltechAUTHORS:20230327-902775000.4
Year: 2023
DOI: 10.2514/6.2023-2399
Progress towards the use of ultra-thin fiber Bragg grating sensors for the in-situ strain measurement of coilable thin composite shells is presented. The first part of this work presents the manufacturing procedure used in the construction of these composite shells with embedded sensors. The second part of this work investigates how embedded ultra-thin fiber Bragg grating sensors affect the bending stiffness and failure curvature of these laminates through the use of the column bending test. The influence of the embedded sensors on the failure of these laminates is further investigated through μCT imaging after failure.https://resolver.caltech.edu/CaltechAUTHORS:20230327-902775000.4Dynamics of the Caltech SSPP deployable structures: structure–mechanism interaction and deployment envelope
https://resolver.caltech.edu/CaltechAUTHORS:20230327-902809000.10
Year: 2023
DOI: 10.2514/6.2023-2065
The Caltech Space Solar Power Project has been developing ultralight deployable space structures consisting of thin-shell composite strips that support photovoltaic and RF elements. These modular, square structures can potentially be scaled to tens of meters in size. This paper studies the interaction between the deployment dynamics of the structure and the deployment mechanism, both experimentally and numerically. Instead of considering a full structure, a quadrant is considered to reduce the number of components and to better focus on the main parameters that affect the deployment behavior. Outcomes of this research will not only benefit the Caltech project but will also contribute to the design of future lightweight deployable space structures that undergo unconstrained dynamic deployment.https://resolver.caltech.edu/CaltechAUTHORS:20230327-902809000.10Multi-configuration rigidity: Theory for statically determinate structures
https://authors.library.caltech.edu/records/4zrv0-w5y55
Year: 2023
DOI: 10.1016/j.ijsolstr.2023.112502
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<p>This paper introduces the concept of multi-configuration rigidity for kinematically indeterminate structures with elastic springs and unilateral constraints. A simple example is provided by a structure with a single mechanism and a spring that engages two different unilateral constraints. In each of these configurations, the structure can rigidly support loads up to a critical magnitude at which the unilateral constraints become inactive. The general design problem of embedding springs throughout a structure to achieve <em>multi-configuration rigidity</em>, with multiple unilateral constraints and springs, is studied. This problem is cast as a <a class="topic-link" title="Learn more about linear program from ScienceDirect's AI-generated Topic Pages" href="https://www.sciencedirect.com/topics/engineering/linear-program">linear program</a> that maximizes the critical loads required to break free from the unilateral constraints, in all target configurations. This problem can be efficiently solved with guarantees of <a class="topic-link" title="Learn more about optimality from ScienceDirect's AI-generated Topic Pages" href="https://www.sciencedirect.com/topics/engineering/optimality">optimality</a>. The formulation is generally applicable to a variety of discrete structures (e.g., linkages, pin-jointed bars, or origami) with unilateral constraints (e.g., contacts or cables).</p>
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<ul class="issue-navigation u-margin-s-bottom u-bg-grey1"></ul>https://authors.library.caltech.edu/records/4zrv0-w5y55Folding kinematics of kirigami-inspired space structures
https://authors.library.caltech.edu/records/bja23-yz438
Year: 2024
DOI: 10.1016/j.ijsolstr.2024.112865
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<p>This paper studies the folding of square, kirigami-inspired space structures consisting of concentrically arranged modular elements formed by thin shells. Localized elastic folds are introduced in the thin shells and different folding strategies can be obtained by varying the location of the folds and the sequence of imposed rotations. Modeling each modular element with rigid rods connected by revolute joints, numerical simulations of the kinematics of folding are obtained, including constraints that represent folding aids and a gravity offload system. These simulations are used to study two specific packaging schemes, and the folding envelopes of a specific structure are analyzed to identify the scheme that is easier to implement in practice. This particular scheme is demonstrated by means of a physical prototype.</p>
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</div>https://authors.library.caltech.edu/records/bja23-yz438