CaltechAUTHORS: Book Chapter
https://feeds.library.caltech.edu/people/Pellegrino-S/book_section.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenThu, 13 Jun 2024 19:45:47 -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:20180614-161010885Simulation 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:20200330-082659500Shape 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:20191016-085828334Optimized 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 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:20110321-085232350Shape 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:20190930-110457762Viscoelastic 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:20190930-110458819Design 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:20190930-110458726Effects 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:20190930-110458917DEORBITSAIL: 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:20191004-152131563Thin 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:20160303-153240359Structural 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:20190826-092412894Characterization 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:20190828-102318305Design 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:20190828-102318423Large 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:20190918-093409950A 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:20190918-090257435Deployment 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:20191218-095027064Folding 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:20191218-112129907Deployable 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:20131120-152814552Ultra-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:20190816-144340709Design 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:20190816-144340816Parylene 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:20140520-140334969Effects 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:20191002-151926429Failure 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:20170622-081730492Optimization 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:20190814-104606776Using 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:20190924-081804330A 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:20191017-082538614Folding 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:20170615-080812634Buckling 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:20190816-144341971Dual-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:20190816-144341883Wrapping 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:20190816-144340621Random 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:20191002-150220868A 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:20160401-100827980Membrane 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:20160930-131912958Methods 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:20160930-131726070A 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:20160909-112312357Folding 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:20190828-095135682Nondestructive 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:20190822-102905667Multilayer 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:20160929-102853368Co-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:20160929-095806840Modular 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:20190821-155916295Vibration 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:20190820-152401055In-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:20190820-154603282Characterization 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:20170614-164611614Impact 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:20181109-074226646Lightweight 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:20181109-075349019Trajectory 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:20170630-094657577Design 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:20181108-154443049Near-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 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:20191114-160021163Ultra-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:20191112-155802266Self-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:20190805-134838958Cure-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:20190806-133219697Stress 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:20190805-134837271Fast 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:20180615-113248296Shape 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:20190404-081554007Attitude 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:20191112-154118926Stability 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:20190805-134838114Parametric 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:20190805-134837694Interface 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:20200110-160834737Sequentially 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:20200113-075647741Buckling 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:20200113-080052698Origami-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:20210112-105612128Reduced-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:20210112-105611714Cable-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:20210514-081314705Fully 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:20220217-686367000Health 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:20220210-928413000High-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:20220210-928394000Propagating 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:20220210-928328000Lightweight 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:20220210-928455000Development 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:20220210-928385000Micromechanics 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:20220210-928345000Launch 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:20220210-928446000Modeling 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:20230327-902890000.24Slew 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:20230327-902813000.11Buckling 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:20230327-902885000.22Launch 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:20230327-902798000.8Nonlinear 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:20230327-902858000.18Strain 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:20230327-902809000.10