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NASA NTRS1991

Ground test validation for precision structures

Future proposed NASA missions will require large precision truss type structures that are deployed or assembled in space. To date, space structures that are important to missions success have been ground tested to validate their performance. Evaluation of the performance requirements of future systems has shown that using current and projected design and test approaches, the structure cannot be adequately validated by ground test. A problem exists since it is believed that unless important structure systems can be validated by ground tests, they will never be adopted for future missions. New design or ground test approaches are necessary to enable future missions. The inability of current approaches to validate future structural systems is discussed.

Wada, Ben K.↗

NASA NTRS2002

Compositionally-Graded Shape Memory Film for Self-Deployment of Membrane Reflectors and Optics

The next generation of space systems will require large apertures in order to image faint targets or cover large areas of Earth. These large apertures must be able to fit inside a launch vehicle fairing, be light enough for launch into orbit, and deploy on orbit with repeatability and reliability. The current state-of-the-art in flight optics is represented by the 4 meter LAMP telescope, with an areal density of 10 km sq m. Development of a Beryllium mirror demonstration article for NGST (Next Generation Space Telescope) at the University of Arizona indicate areal densities of 0.5 kg sq m with flight hardware in the 12 meter range. With progressive improvements in existing deployment, packaging, and structural technologies, the size of optics and reflectors will continue to increase, while mass is reduced. However, without a breakthrough in materials, packaging and/or deployment technologies, the goal for Gossamer structures of 0.1 kg sq m is unachievable for the near and mid-term NASA missions. Membrane technology provides the best hope of achieving such low areal densities. In combination with advances in membrane materials and structures, development of revolutionary techniques for deployment systems can provide significant improvements in large aperture technology. In this paper, the results of a six-month Phase I research effort to demonstrate the application of thin film NiTi to aerospace-qualified membrane and mesh materials are presented. Deposition of shape memory thin film was achieved Astromesh (trademark) metal mesh and CP-1, and optical-quality polymer membrane. Not only was full-coating deposition demonstrated, but also small segment deposition which holds potential for local surface control. Deployment of these materials was also demonstrated, setting the stage for the development of a larger test article.

Hill, Lisa↗

NASA NTRS2009

FPGA-Based Networked Phasemeter for a Heterodyne Interferometer

A document discusses a component of a laser metrology system designed to measure displacements along the line of sight with precision on the order of a tenth the diameter of an atom. This component, the phasemeter, measures the relative phase of two electrical signals and transfers that information to a computer. Because the metrology system measures the differences between two optical paths, the phasemeter has two inputs, called measure and reference. The reference signal is nominally a perfect square wave with a 50- percent duty cycle (though only rising edges are used). As the metrology system detects motion, the difference between the reference and measure signal phases is proportional to the displacement of the motion. The phasemeter, therefore, counts the elapsed time between rising edges in the two signals, and converts the time into an estimate of phase delay. The hardware consists of a circuit board that plugs into a COTS (commercial, off-the- shelf) Spartan-III FPGA (field-programmable gate array) evaluation board. It has two BNC inputs, (reference and measure), a CMOS logic chip to buffer the inputs, and an Ethernet jack for transmitting reduced-data to a PC. Two extra BNC connectors can be attached for future expandability, such as external synchronization. Each phasemeter handles one metrology channel. A bank of six phasemeters (and two zero-crossing detector cards) with an Ethernet switch can monitor the rigid body motion of an object. This device is smaller and cheaper than existing zero-crossing phasemeters. Also, because it uses Ethernet for communication with a computer, instead of a VME bridge, it is much easier to use. The phasemeter is a key part of the Precision Deployable Apertures and Structures strategic R&D effort to design large, deployable, segmented space telescopes.

Rao, Shanti↗

NASA NTRS1986

Space station structures development

A study of three interrelated tasks focusing on deployable Space Station truss structures is discussed. Task 1, the development of an alternate deployment system for linear truss, resulted in the preliminary design of an in-space reloadable linear motor deployer. Task 2, advanced composites deployable truss development, resulted in the testing and evaluation of composite materials for struts used in a deployable linear truss. Task 3, assembly of structures in space/erectable structures, resulted in the preliminary design of Space Station pressurized module support structures. An independent, redundant support system was developed for the common United States modules.

Teller, V. B.↗

NASA NTRS2003

Deployment Simulation Methods for Ultra-Lightweight Inflatable Structures

Two dynamic inflation simulation methods are employed for modeling the deployment of folded thin-membrane tubes. The simulations are necessary because ground tests include gravity effects and may poorly represent deployment in space. The two simulation methods are referred to as the Control Volume (CV) method and the Arbitrary Lagrangian Eulerian (ALE) method. They are available in the LS-DYNA nonlinear dynamic finite element code. Both methods are suitable for modeling the interactions between the inflation gas and the thin-membrane tube structures. The CV method only considers the pressure induced by the inflation gas in the simulation, while the ALE method models the actual flow of the inflation gas. Thus, the transient fluid properties at any location within the tube can be predicted by the ALE method. Deployment simulations of three packaged tube models; namely coiled, Z-folded, and telescopically-folded configurations, are performed. Results predicted by both methods for the telescopically-folded configuration are correlated and computational efficiency issues are discussed.

Wang, John T.↗

NASA NTRS2007

CHEM-Based Self-Deploying Planetary Storage Tanks

A document proposes self-deploying storage tanks, based on the cold elastic hibernated memory (CHEM) concept, to be used on remote planets. The CHEM concept, described in previous NASA Tech Briefs articles, involves the use of open-cell shape-memory-polymer (SMP) foam sandwich structures to make lightweight, space-deployable structures that can be compressed for storage and can later be expanded, then rigidified for use. A tank according to the proposal would be made of multiple SMP layers (of which at least one could be an SMP foam). The tank would be fabricated at full size in the rigid, deployed condition at ambient temperature, the SMP material(s) having been chosen so that ambient temperature would be below the SMP glass-transition temperature (T(sub g)). The tank would then be warmed to a temperature above T(sub g), where it would be compacted and packaged, then cooled to below T(sub g) and kept there during launch and transport to a distant planet. At the assigned position on the planet, the compacted tank would be heated above T(sub g) by the solar radiation making it rebound to its original size and shape. Finally, the tank would be rigidified through natural cooling to below T(sub g) in the planetary ambient environment.

Sokolowski, Witold↗

NASA NTRS1989

Advances in large inflatable reflectors

For most applications in space for which they were tried, inflatable structures show a significant weight reduction when compared to mechanical structures. Inflatables are unmatched when compared to mechanical structures when packaged volume is considered. The reliability of deployment of inflatable structures was known for years. When properly designed, such a system is inherently more reliable because it has very few points of failure. Fully inflatable vs. rigidized inflatable structures are discussed. The L'Garde solar concentrator experience is described. Reflector surface and cylinder rigidization, improvement in gore design tools, and expected advances in rigidization schemes with near future are examined.

Thomas, M.↗

NASA NTRS2005

Materials Challenges in Space Exploration

United States civil space program administered by National Aeronautics and Space Administration has a new strategic direction to explore the solar system. This new 'vision for space exploration' encompasses a broad range of human and robotic missions, including the Moon. Mars and destinations beyond. These missions require advanced systems and capabilities that will accelerate the development of many critical technologies, including advanced materials and structural concepts. Specifically, it is planned to develop high-performance materials for vehicle structures, propulsion systems, and space suits; structural concepts for modular assembly for space infrastructure: lightweight deployable and inflatable structures for large space systems and crew habitats; and highly integrated structural systems and advanced thermal management systems for reducing launch mass and volume. This paper will present several materials challenges in advanced space systems-high performance structural and thermal materials, space durable materials, radiation protection materials, and nano-structural materials. Finally, the paper will take a look at the possibility of utilizing materials in situ, i.e., processing materials on the surface of the Moon and Mars.

Bhat, Biliyar N.↗

NASA NTRS2005

Materials Challenges in Space Exploration

United States civil space program administered by National Aeronautics and Space Administration (NASA) has a new strategic direction to explore the solar system. This new 'vision for space exploration' encompasses a broad range of human and robotic missions, including the Moon, Mars and destinations beyond. These missions require advanced systems and capabilities that will accelerate the development of many critical technologies, including advanced materials and structural concepts. Specifically, it is planned to develop high-peformance materials for vehicle structures, propulsion systems, and space suits; structural concepts for modular assembly for space infrastructure; lightweight deployable and inflatable structures for large space systems and crew habitats; and highly integrated structural systems and advanced thermal management systems for reducing launch mass and volume. This paper will present several materials challenges in advanced space systems-high performance structural and thermal materials, space durable materials, radiation protection materials, and nano- structural materials. The paper will also address smart materials and structures and examine space environmental effects on materials and methods of mitigating them. Finally, the paper will take a look at the possibility of utilizing materials in situ, i.e., processing and using desired materials on the surface of the Moon and Mars.

Bhat, Biliyar N.↗

NASA NTRS2004

Development and Ground Testing of a Compactly Stowed Scalable Inflatably Deployed Solar Sail

This paper discusses the solar sail design and outlines the interim accomplishments to advance the technology readiness level (TRL) of the subsystem from 3 toward a technology readiness level of 6 in 2005. Under Phase II of the program many component test articles have been fabricated and tested successfully. Most notably an unprecedented section of the conically deployed rigidizable sail support beam, the heart of the inflatable rigidizable structure, has been deployed and tested in the NASA Goddard thermal vacuum chamber with good results. The development testing validated the beam packaging and deployment. The inflatable conically deployed, Sub Tg rigidizable beam technology is now in the TRL 5-6 range. The fabricated masses and structural test results of our beam components have met predictions and no changes to the mass estimates or design assumptions have been identified adding great credibility to the design. Several quadrants of the Mylar sail have also been fabricated and successfully deployed validating our design, manufacturing, and deployment techniques.

Lichodziejewski, David↗

NASA NTRS1985

Synchronously Deployable Truss

Double-layered truss structure compactly packaged and sychronously deployed. Synchronously deployable truss constructed of two surface layers of struts, arranged in triangles, connected by "tripods" of equal-length core struts. Mechanism powered by passive spring and damped by hydraulic-damping cylinder. When released, spring drives slider linked to core and surface struts. Variety of truss geometries, including curved structures, comtemplated.

Bush, H. G.↗

NASA NTRS1978

Deployable antenna demonstration study

A demonstration system and shuttle flight program was defined to demonstrate packaging, transportation, erection, and structural integrity of a large deployable antenna concept. An analysis of deployable antenna requirements indicates that (1) erectable structures are clearly applicable to very high precision (above 50 GHz) antennas (10 to 30 m); (2) deployable structures are light weight, applicable to moderate precision (below 14 GHz) large antennas (up to 300 m); and (3) both deployable and erectable apply to small and large antenna platforms with common utilities.

Thompson, W.↗

NASA NTRS1979

New space initiatives through large generic structures

New possibilities in satellite communications, surveillance, and orbital experimentation provided by the capability to construct and deploy Large Space Structures (LSS) are presented. The advent of the Shuttle will allow deployment of larger antennas with much larger gain sizes, noting new applications in communications, radiometry, and radar in frequencies from 0.24 to 14 GHz. Applications in multi-beam communication which can hold spot sizes on the ground down to 30 miles in diameter, new applications of the large aperture radar antenna, and estimates of soil moisture by the microwave radiometer are discussed. The Solar Power Satellite consisting of a large solar collector orbiting the earth at geosynchronous altitude over the equator which requires ability to construct LSS in space is described, noting the design of solar cells and materials of construction, including graphite composites and aluminum alloys. Space construction procedures and equipment are considered, noting that the most likely procedure would deliver the subsystems to orbit separately, and then construct the spacecraft on-orbit and assemble the satellite.

Johnson, R. W.↗

NASA NTRS2002

Finite Element Analysis of Wrinkled Membrane Structures for Sunshield Applications

The deployable sunshield is an example of a gossamer structure envisioned for use on future space telescopes. The basic structure consists of multiple layers of pretensioned, thin-film membranes supported by deployable booms. The prediction and verification of sunshield dynamics has been identified as an area in need of technology development due to the difficulties inherent in predicting nonlinear structural behavior of the membranes and because of the challenges involved. in ground testing of the full-scale structure. This paper describes a finite element analysis of a subscale sunshield that has been subjected to ground testing in support of the Next Generation Space Telescope (NGST) program. The analysis utilizes a nonlinear material model that accounts for wrinkling of the membranes. Results are presented from a nonlinear static preloading analysis and subsequent dynamics analyses to illustrate baseline sunshield structural characteristics. Studies are then described which provide further insight into the effect of membrane. preload on sunshield dynamics and the performance of different membrane modeling techniques. Lastly, a comparison of analytical predictions and ground test results is presented.

Johnston, John D.↗

NASA NTRS1986

Structural dynamic analysis of the Large Deployable Reflector

The dynamic performance of the primary mirror of the Large Deployable Reflector (LDR) is analyzed under conditions of typical external disturbances that would be encountered during normal space operation. The performance assessment is based upon the difference between the figure distortion errors of the incoming image and the mission figure tolerance requirements (rms surface accuracy error and jitter). The need for additional figure control of the incoming image is assessed, and other alternatives for figure control are presented, such as increased structural damping effects due to the uncertainty in the real damping characteristics.

Andersen, G. C.↗

NASA NTRS2011

Experimental and Analytical Evaluation of a Composite Honeycomb Deployable Energy Absorber

In 2006, the NASA Subsonic Rotary Wing Aeronautics Program sponsored the experimental and analytical evaluation of an externally deployable composite honeycomb structure that is designed to attenuate impact energy during helicopter crashes. The concept, which is designated the Deployable Energy Absorber (DEA), utilizes an expandable Kevlar honeycomb structure to dissipate kinetic energy through crushing. The DEA incorporates a unique flexible hinge design that allows the honeycomb to be packaged and stowed flat until needed for deployment. A variety of deployment options such as linear, radial, and/or hybrid methods can be used. Experimental evaluation of the DEA utilized a building block approach that included material characterization testing of its constituent, Kevlar -129 fabric/epoxy, and flexural testing of single hexagonal cells. In addition, the energy attenuation capabilities of the DEA were demonstrated through multi-cell component dynamic crush tests, and vertical drop tests of a composite fuselage section, retrofitted with DEA blocks, onto concrete, water, and soft soil. During each stage of the DEA evaluation process, finite element models of the test articles were developed and simulations were performed using the explicit, nonlinear transient dynamic finite element code, LS-DYNA. This report documents the results of the experimental evaluation that was conducted to assess the energy absorption capabilities of the DEA.

Jackson, Karen E.↗

NASA NTRS2005

Structural Analysis of an Inflation-Deployed Solar Sail With Experimental Validation

Under the direction of the NASA In-Space Propulsion Technology Office, the team of L Garde, NASA Jet Propulsion Laboratory, Ball Aerospace, and NASA Langley Research Center has been developing a scalable solar sail configuration to address NASA s future space propulsion needs. Prior to a flight experiment of a full-scale solar sail, a comprehensive phased test plan is currently being implemented to advance the technology readiness level of the solar sail design. These tests consist of solar sail component, subsystem, and sub-scale system ground tests that simulate the vacuum and thermal conditions of the space environment. Recently, two solar sail test articles, a 7.4-m beam assembly subsystem test article and a 10-m four-quadrant solar sail system test article, were tested in vacuum conditions with a gravity-offload system to mitigate the effects of gravity. This paper presents the structural analyses simulating the ground tests and the correlation of the analyses with the test results. For programmatic risk reduction, a two-prong analysis approach was undertaken in which two separate teams independently developed computational models of the solar sail test articles using the finite element analysis software packages: NEiNastran and ABAQUS. This paper compares the pre-test and post-test analysis predictions from both software packages with the test data including load-deflection curves from static load tests, and vibration frequencies and mode shapes from structural dynamics tests. The analysis predictions were in reasonable agreement with the test data. Factors that precluded better correlation of the analyses and the tests were uncertainties in the material properties, test conditions, and modeling assumptions used in the analyses.

Sleight, David W.↗

NASA NTRS1989

Support trusses for large precision segmented reflectors - Preliminary design and analysis

The Precision Segmented Reflector (PSR) primary structures plan is outlined. Geometries and design considerations for erectable and deployable reflector support structures are discussed. Support truss requirements and goals for the PSR are given, and the results of static and dynamic analyses of a prototype four meter diameter structure are presented. In addition, similar results are presented for two 20-meter diameter support trusses. Implications of the analyses for the PSR program are considered and the formulation and limitations of current PSR finite element models are discussed. It is shown that if the secondary optical system is supported by a simple tripod design, the first six vibration modes are likely to be dominated by the secondary system. The 20-meter diameter support trusses are found to be quite stiff for structures of such large size.

Collins, Timothy J.↗