{"project":{"acronym":"","projectId":88560,"title":"New Designs for Modular Ultra-Light Precision Space Structures","primaryTaxonomyNodes":[{"taxonomyNodeId":10865,"taxonomyRootId":8816,"parentNodeId":10864,"level":3,"code":"TX12.2.1","title":"Lightweight Concepts","definition":"Lightweight concepts are efficient structures and structural systems using new and innovative approaches to develop beyond-state-of-the-art mass reductions for affordable, enhanced performance, reliable, and environmentally responsible aerospace applications.","exampleTechnologies":"Components for space vehicles and surface habitats, in-space depots and landers, solar or antenna arrays, complex precision deployables, propulsion systems, and terrestrial airframes and engines which function either as primary load bearing or as secondary structures. The technologies used for these components may include either rigid construction (e.g., shell or truss structures) or expandable configurations (e.g., inflatable structures) having efficient structural geometries (e.g., hat-stiffened shells) constructed from advanced materials (e.g., polymer matrix composites) using advanced fabrication methods (e.g., additive manufacturing)","hasChildren":false,"hasInteriorContent":true}],"startTrl":2,"currentTrl":3,"endTrl":3,"benefits":"The success of this project will help in achieving NASA's goals for future space exploration by developing low technology readiness concepts and enabling large space-based observatories.","description":"In a shared effort of advancing our scientific understanding of planets, stars, and galaxies, space agencies and astronomical centers have been building increasingly large telescopes. These observatories allow us to collect more light and extend angular resolution to detect fainter objects in the cosmos. While ground-based telescopes are fundamentally limited by atmospheric distortion and absorption, space-based telescopes avoid these disadvantages but introduce new challenges. The aperture size of a space-telescope is driven by scientific requirements for resolution and sensitivity, but it is constrained by the capabilities of launch vehicles. Segmented apertures relax some of the volume constraint, but a natural question is whether the primary should be a single large foldable mirror structure (like James Webb Space Telescope), or a modular structure suitable for in-space robotic assembly. The second option, which will be investigated in this research, overcomes volume and mass limitations of a single launch vehicle, allowing telescope components to be launched incrementally. The goal of my research project is to provide ground-breaking designs for modular, ultra-light, and precision space structures, suitable for the development of extremely large optical reflectors (i.e. 10 m and above) that are robotically assembled in space. There are three main advantages related to this proposed approach: first, substantially reducing the cost of building large space optical reflectors by developing new and less expensive solutions, second, implementing a lightweight technology by utilizing ultra-thin composite materials, and third, increasing system redundancy by adopting an architecture that consists of separate modules that can be replaced. There are many steps involved in the design of innovative structures. Here, I identify the four main tasks required to complete the proposed research: numerical simulations, material characterization, composite manufacturing, and testing and validation. Numerical simulations will help identify optimal design configurations and predict possible failure modes of the modular unit. Material characterization will be necessary to study the viscoelastic effects of long-term storage. Finally, manufacturing and testing of the modules will complete the design process and help find solutions. The modular unit promises to meet NASA's requirements for packaging-efficient, lightweight, low-cost, reliable, and precision structures, by incorporating established techniques and ground-breaking approaches. The success of this project will help in achieving NASA's goals for future space exploration by developing low technology readiness concepts and enabling large space-based observatories.","startYear":2016,"startMonth":8,"endYear":2020,"endMonth":2,"statusDescription":"Completed","principalInvestigators":[{"contactId":430623,"canUserEdit":false,"firstName":"Sergio","lastName":"Pellegrino","fullName":"Sergio Pellegrino","fullNameInverted":"Pellegrino, Sergio","primaryEmail":"sergio.pellegrino@jpl.nasa.gov","publicEmail":true,"nacontact":false}],"programDirectors":[{"contactId":84634,"canUserEdit":false,"firstName":"Claudia","lastName":"Meyer","fullName":"Claudia M Meyer","fullNameInverted":"Meyer, Claudia M","middleInitial":"M","primaryEmail":"claudia.m.meyer@nasa.gov","publicEmail":true,"nacontact":false}],"programExecutives":[{"contactId":84634,"canUserEdit":false,"firstName":"Claudia","lastName":"Meyer","fullName":"Claudia M Meyer","fullNameInverted":"Meyer, Claudia M","middleInitial":"M","primaryEmail":"claudia.m.meyer@nasa.gov","publicEmail":true,"nacontact":false}],"programManagers":[{"contactId":183514,"canUserEdit":false,"firstName":"Hung","lastName":"Nguyen","fullName":"Hung D Nguyen","fullNameInverted":"Nguyen, Hung D","middleInitial":"D","primaryEmail":"hung.d.nguyen@nasa.gov","publicEmail":true,"nacontact":false}],"projectManagers":[{"contactId":491950,"canUserEdit":false,"firstName":"William","lastName":"Doggett","fullName":"William R Doggett","fullNameInverted":"Doggett, William R","middleInitial":"R","primaryEmail":"bill.doggett@nasa.gov","publicEmail":true,"nacontact":false}],"coInvestigators":[{"contactId":430161,"canUserEdit":false,"firstName":"Serena","lastName":"Ferraro","fullName":"Serena Ferraro","fullNameInverted":"Ferraro, Serena","primaryEmail":"sferraro@caltech.edu","publicEmail":false,"nacontact":false}],"website":"https://www.nasa.gov/strg#.VQb6T0jJzyE","libraryItems":[],"transitions":[{"transitionId":75936,"projectId":88560,"transitionDate":"2020-02-01","path":"Closed Out","details":"Shell structures with cutouts are widely used in architectural and engineering applications. For thin, lightweight, and deployable space structures, cutouts are cleverly positioned to fold and store the structure in a small volume. To maintain shape accuracy, these structures must fold without becoming damaged and must be stiff in their deployed configurations. Intuitive designs often fail to satisfy these two requirements. This research proposes solutions to the topology optimization of composite, thin shell structures with cutouts. First, a novel optimization algorithm was developed that makes no assumptions on the initial number, shape, and location of cutouts on deployable thin shells. The algorithm uses a density-based approach, which distributes the material within the structure by assigning a density parameter to discretized locations. This parametrization of the design domain allows for the finding of new features and the connectivity of the domain, thus providing a completely general formulation to the optimization problem. The goal is to study the effects of volume and stress constraints imposed in a deformed configuration of thin shell structures. While classical topology optimization studies focus on finding solutions to linear problems, this method is applicable to geometrically nonlinear problems and implements stress constraints in the deformed, and hence most stressed, configuration of these shells. A mathematical formulation of the optimization problem and interpolation schemes for stiffness tensor, volume, and stress are developed. A sensitivity analysis of objective function, volume, and stress constraints is provided. Finally, solutions for a thin plate and a tape spring are proposed. Density-based methods are computationally expensive when applied to large structures and complex shapes because of the large number of design variables. To address these challenges, two optimization methods that provide more specific solutions to the problem of composite, deployable shells are proposed. The first method uses level sets to parametrize the cutouts, thereby restricting the design space and simultaneously limiting the number of design variables. This greatly reduces the computational cost. Using this approach, successful solutions are found for stiff, composite, thin shells with complex shapes that can fold without becoming damaged. The second method uses a spline representation of the contour of a single cutout on the shell, thus performing fine tuning of the shape of the cutout. Modeling techniques that simulate localized strain and experimental methods for studying the quasi-static folding of these composite shells are developed. A laminate failure criterion suitable for thin, plain-weave composites is used in simulations to predict the onset of failure in folded shells. Numerical results are validated with folding experiments that demonstrated good agreement with numerical solutions. Lastly, it was discovered that many of the best performing solutions have multiple closely spaced cutouts, as opposed to current designs for deployable space structures that have fewer large cutouts. This leads to the formation of small strips of material between cutouts. Hence, the behavior of thin, plain-weave composite material was characterized and the first study on size-scaling effects at small length scales (≤ 15 mm) in this type of material was performed. Size-scaling effects on stiffness and strength shown in this study were introduced in numerical simulations of deployable thin shells. The study demonstrates that the prediction of the onset of failure in folded shells strongly depends on these size effects. Numerical predictions are corroborated by an experimental investigation of localized damage in thin strips of material forming between cutouts. Deployable shells resulting from the optimization studies are built and tested and localized damage is measured via digital volume correlation techniques. In conclusion, this research provides the first extensive study on topology optimization of deployable, composite thin shells using a geometrically nonlinear model and imposing stress constraints in the deformed configuration. The objective is to find non intuitive shapes of thin shells that can fold without being damaged, while also maximizing the deployed stiffness. The work has demonstrated that size-scaling effects in thin, plain-weave composites at small length scales produce a reduction in stiffness and strength of this type of material, thus affecting predictions of the onset of failure on deployable shell structures. ","infoText":"Closed out","infoTextExtra":"","dateText":"February 2020"}],"responsibleMd":{"acronym":"STMD","canUserEdit":false,"city":"","external":false,"linkCount":0,"organizationId":4875,"organizationName":"Space Technology Mission Directorate","organizationType":"NASA_Mission_Directorate","naorganization":false,"organizationTypePretty":"NASA Mission Directorate"},"program":{"acronym":"STRG","active":true,"description":"
\tThe Space Technology Research Grants Program will accelerate the development of "push" technologies to support the future space science and exploration needs of NASA, other government agencies and the commercial space sector. Innovative efforts with high risk and high payoff will be encouraged. The program is composed of two competitively awarded components.
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