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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Tubular space truss structure for SKITTER 2 robot

The Skitter 2 is a three legged transport vehicle designed to demonstrate the principle of a tripod walker in a multitude of environments. The tubular truss model of Skitter 2 is a proof of principal design. The model will replicate the operational capabilities of Skitter 2 including its ability to self-right itself. The project's focus was on the use of light weight tubular members in the final structural design. A strong design for the body was required as it will undergo the most intense loading. Triangular geometry was used extensively in the body, providing the required structural integrity and eliminating the need for cumbersome shear panels. Both the basic femur and tibia designs also relied on the strong geometry of the triangle. An intense literature search aided in the development of the most suitable weld techniques, joints, linkages, and materials required for a durable design. The hinge design features the use of spherical rod end bearings. In order to obtain a greater range of mobility in the tibia, a four-bar linkage was designed which attaches both to the femur and the tibia. All component designs, specifically the body, femur, and the tibia were optimized using the software package IDEAS 3.8A Supertab. The package provided essential deformation and stress analysis information on each component's design. The final structure incurred only a 0.0544 inch deflection in a maximum (worst case) loading situation. The highest stress experienced by any AL6061-T6 tubular member was 1920 psi. The structural integrity of the final design facilitated the use of Aluminum 6061-T6 tubing. The tubular truss structure of Skitter 2 is an effective and highly durable design. All facets of the design are structurally sound and cost effective.

Beecham, Richard↗
NASA NTRS1985

Promising quantitative nondestructive evaluation techniques for composite materials

Some recent results in the area of the ultrasonic, acoustic emission, thermographic, and acousto-ultrasonic NDE of composites are reviewed. In particular, attention is given to the progress in the use of ultrasonic attenuation, acoustic emission (parameter) delay, liquid-crystal thermography, and the stress wave factor in structural integrity monitoring of composite materials. The importance of NDE flaw significance characterizations is emphasized since such characterizations can directly indicate the appropriate NDE technique sensitivity requirements. The role of the NDE of flawed composites with and without overt defects in establishing quantitative accept/reject criteria for structural integrity assessment is discussed.

Williams, J. H., Jr.↗
NASA NTRS1972

SIT-5 system development.

A 5-cm structurally integrated ion thruster (SIT-5) has been developed for attitude control and stationkeeping of synchronous satellites. With two-dimension thrust-vectoring grids, a first generation unit has demonstrated a thrust of 0.56 mlb at a beam voltage of 1200 V, total mass efficiency of 64%, and electrical efficiency of 46.8%. Structural integrity is demonstrated with a dielectric-coated grid for shock (30 G), sinusoidal (9 G), and random (19.9 G rms) accelerations. System envelope is 31.8 cm long by 13.9 cm flange bolt circle, with a mass of 8.5 kg, including 6.2 kg mercury propellant. Characteristics of a second-generation unit indicate significant performance gains.

Hyman, J., Jr.↗
NASA NTRS1993

Mutations in the putative calcium-binding domain of polyomavirus VP1 affect capsid assembly

Calcium ions appear to play a major role in maintaining the structural integrity of the polyomavirus and are likely involved in the processes of viral uncoating and assembly. Previous studies demonstrated that a VP1 fragment extending from Pro-232 to Asp-364 has calcium-binding capabilities. This fragment contains an amino acid stretch from Asp-266 to Glu-277 which is quite similar in sequence to the amino acids that make up the calcium-binding EF hand structures found in many proteins. To assess the contribution of this domain to polyomavirus structural integrity, the effects of mutations in this region were examined by transfecting mutated viral DNA into susceptible cells. Immunofluorescence studies indicated that although viral protein synthesis occurred normally, infective viral progeny were not produced in cells transfected with polyomavirus genomes encoding either a VP1 molecule lacking amino acids Thr-262 through Gly-276 or a VP1 molecule containing a mutation of Asp-266 to Ala. VP1 molecules containing the deletion mutation were unable to bind 45Ca in an in vitro assay. Upon expression in Escherichia coli and purification by immunoaffinity chromatography, wild-type VP1 was isolated as pentameric, capsomere-like structures which could be induced to form capsid-like structures upon addition of CaCl2, consistent with previous studies. However, although VP1 containing the point mutation was isolated as pentamers which were indistinguishable from wild-type VP1 pentamers, addition of CaCl2 did not result in their assembly into capsid-like structures. Immunogold labeling and electron microscopy studies of transfected mammalian cells provided in vivo evidence that a mutation in this region affects the process of viral assembly.

Non-NASA Center↗
NASA NTRS1981

Thermal and aerothermal performance of a titanium multiwall thermal protection system

A metallic thermal protection system (TPS) concept the multiwall designed for temperature and pressure at Shuttle body point 3140 where the maximum surface temperature is approximately 811 K was tested to evaluate thermal performance and structural integrity. A two tile model of titanium multiwall and a model consisting of a low temperature reusable surface insulation (LRSI) tiles were exposed to 25 simulated thermal and pressure Shuttle entry missions. The two systems performed the same, and neither system deteriorated during the tests. It is indicated that redesign of the multiwall tiles reduces tile thickness and/or weight. A nine tile model of titanium multiwal was tested for radiant heating and aerothermodynamics. Minor design changes that improve structural integrity without having a significant impact on the thermal protection ability of the titanium multiwall TPS are identified. The capability of a titanium multiwall thermal protection system to protect an aluminum surface during a Shuttle type entry trajectory at locations on the vehicle where the maximum surface temperature is below 811 K is demonstrated.

Avery, D. E.↗
NASA NTRS1990

In-service health monitoring of composite structures

The aerospace industry is witnessing a vast utilization of composites in critical structural applications and anticipates even more use of them in future aircraft. Therefore, a definite need exists for a composite health monitoring expert system to meet today's current needs and tomorrow's future demands. The primary goal for this conceptual health monitoring system is functional reliably for in-service operation in the environments of various composite structures. The underlying philosophy of this system is to utilize proven vibration techniques to assess the structural integrity of a fibrous composite. Statistical methods are used to determine if the variances in the measured data are acceptable for making a reliable decision on the health status of the composite. The flexible system allows for algorithms describing any composite fatigue or damage behavior characteristic to be provided as an input to the system. Alert thresholds and variances can also be provided as an input to this system and may be updated to allow for future changes/refinements in the composite's structural integrity behavior.

Pinto, Gino A.↗
NASA NTRS2009

Modal Vibration Analysis of Large Castings

The art of experimental modal vibration analysis (MVA) has been extended to apply to large castings. This extension was made to enable the use of experimental MVA as a relatively inexpensive, simple means of assessing the internal structural integrity of tread shoes of crawler transporters used to move spacecraft to the launch pad at Kennedy Space Center. Each tread shoe is made from cast iron and weighs about a ton (has a mass .907 kg). The present extended version of experimental MVA could also be applied to other large castings. It could be especially useful to manufacturers as a means of rapidly discriminating against large castings that contain unacceptably large concentrations of internal defects. The use of experimental MVA to assess structural integrity is not new. What are new here are those aspects of the extension of experimental MVA that pertain to the application of MVA to objects so massive that it may not be practical or cost effective to mount them in special test fixtures that impose special test boundary conditions to test them in place under normal conditions of use.

Werlink, Rudolph J.↗
NASA NTRS2016

Atg12 Maintains Skeletal Integrity by Modulating Pro-Osteoclastogenic Signals and Chondrocyte Differentiation

Weightlessness and radiation, two unique elements of space, profoundly decreases bone mass. This bone loss is attributed to increased activity of bone-resorbing osteoclasts and functional changes in bone-forming osteoblasts, cells that give rise to mature osteocytes. Our long-term goal is to identify signaling pathways that may be targeted to mitigate bone loss in scenarios of space exploration, radiotherapy and accidental radiation exposure. We have previously shown that exposure of MLO-Y4 osteocyte-like cells to simulated space radiation (56Fe) increased the expression of the pro-osteoclastogenic gene rankl and decreased protein levels of LC3B-II, a key player in autophagy. In this current study, we aimed to further elucidate the role of autophagy in maintaining structural integrity of the skeleton. We hypothesize that loss of autophagy in bone leads to an imbalance in pro-osteoclastogenic and pro-osteogenic signals, resulting in net bone loss. To test our hypothesis we performed global postnatal deletion of Atg12 using tamoxifeninducible Cre recombinase under the control of the CAG promoter. Six-week-old CAGCreERT2/ FloxAtg12 animals were treated daily with Tamoxifen or Vehicle (Control, oil only) for five days and euthanasia performed two weeks after the onset of treatment. Percent change in body weights (prior to treatment and at euthanasia) was not significantly different between treatment groups within the same gender. Compared to Vehicle (Control) groups, Tamoxifen (Atg12 iKO) groups showed decreased LC3B-I to II conversion and increased p62 protein levels, consistent with loss of autophagy. Quantitative PCR revealed increased expression of proosteoclastogenic cytokines mcp1 and rankl in bone and marrow respectively in male iKOs compared to male controls. Expression levels of these genes were not significantly altered in the Atg12 iKO females compared to females controls. Microcomputed tomography of tibiae revealed decreased cortical bone volume, cortical thickness and periosteal perimeter consistent with bone loss; and a longer primary spongiosa in male Atg12 iKOs display compared to male controls. These decrements were less pronounced in the female Atg12 iKOs. Cancellous bone structure was not significantly different between iKOs and controls in both genders. Histological analysis also revealed that compared to male controls, male iKOs showed a profound increase in chondrocyte column length of the growth plate with hyper-expansion of both proliferating and hypertrophic zones. Taken together, these findings indicate that autophagy plays an important role in the maintenance of bone structural integrity by mediating the production of proosteoclastogenic signals and regulating chondrocyte proliferation and differentiation.

autophagy↗
NASA NTRS1988

Fracture toughness computational simulation of general delaminations in fiber composites

A procedure is described to computationally simulate composite laminate fracture toughness in terms of strain energy release rate (SERR). It is also used to evaluate the degradation in laminate structural integrity in terms of displacements, loss in stiffness, loss in vibration frequencies and loss in buckling resistance. Specific laminates are selected for detail studies in order to demonstrate the generality of the procedure. These laminates had center delaminations, off-center delaminations, and pocket delaminations (center and off-center) at the free-edge and center delaminations at the interior. The laminates had two different thicknesses and were made from three different materials. The results obtained are presented in graphical form to illustrate the effects of delamination on the laminate structural integrity and on the laminate strain energy release rate (composite fracture toughness).

Murthy, P. L. N.↗
NASA NTRS1988

Fracture toughness computational simulation of general delaminations in fiber composites

A procedure is described to computationally simulate composite laminate fracture toughness in terms of strain energy release rate. It is also used to evaluate the degradation in laminate structural integrity in terms of displacements, loss in stiffness, loss in vibration frequencies and loss in buckling resistance. Specific laminates are selected for detail studies in order to demonstrate the generality of the procedure. These laminates had center delaminations, off-center delaminations, and pocket delaminations (center and off-center) at the free-edge and center delaminations at the interior. The laminates had two different thicknesses and were made from three different materials. The results obtained are presented in graphical form to illustrate the effects of delamination on the laminate structural integrity and on the laminate strain energy release rate (composite fracture toughness).

Wilt, T. E.↗
NASA NTRS2000

A Reliable Earth Return System for Safe Recovery of Mars Samples

The objective of a Mars sample return mission is to bring selected Mars surface materials to Earth. Numerous approaches for the Earth-return segment have been analyzed including propulsive or aerocapture return to low-Earth orbit followed by Space Shuttle rendezvous and direct entry. Of these approaches, ballistic entry of a small capsule terminating in a ground landing has been shown to be the lowest risk strategy. Over the past two years, significant work has been performed towards development of a robust direct entry vehicle for Mars sample return. In June 1999, the NASA Planetary Protection Officer provided initial guidance to the former Mars Sample Return Project. The sample return phase of the mission was assigned a restricted Earth return planetary protection classification. The draft mission requirement states that the total mean probability of release of unsterilized Mars material into the Earth;s biosphere must be less than 1.0E-06 (1 in a million). This strict requirement drives the approach and design of the Earth return system. To meet this requirement, selection of the Earth return strategy and development of the Earth return system must be guided by risk, not performance, based decisions. An initial Probabilistic Risk Assessment (PRA) was performed to address the direct entry Earth return system containment assurance reliability and to identify high-risk elements of this system. The results of this PRA identified risk elements that include thermal protection system performance during entry, spin-eject orientation and aerodynamic stability during entry, structural integrity under atmospheric deceleration and impact loads, and tracking/recovery of this system. This initial probabilistic risk quantification demonstrates that, with the proper development program, a prototypical direct entry design can satisfy the containment assurance reliability requirement. Through the current Mars Sample Return Advanced Technology Development effort, an extensive design, analysis, and test program is presently proceeding with the aim of reducing the containment assurance risk of this system. This technology development effort, guided by a continuing PRA, focuses on key risk areas of a direct entry Earth return system including: the thermal protection system, impact dynamics, structural performance, aerodynamic stability, and ground recovery. This development program will culminate in a system validation flight test, 1-2 years prior to launch of the flight system. This flight test would include the launch, entry, and recovery of a full-scale Earth return system, as a scientific validation of the key risk elements to verify nominal design performance. The results of the initial PRA suggested several dominant failure sequences that can be validated in a flight test. These include: demonstrating the thermal protection system reliability and performance during entry, demonstrating the spin-eject orientation and aero-dynamic stability during entry, demonstrating the structural integrity under atmospheric deceleration and impact loads, and demonstrating tracking and recovery of the Earth return system. This single test will directly address over 50% of the total containment assurance risk elements. This presentation will begin by presenting the relative risk of various Earth return strategies. The results of the initial probabilistic risk assessment will be presented followed by a discussion of the development accomplishments and plans for demonstration of a highly reliable direct entry Earth return system.

Braun, R.↗
NASA NTRS2010

Crash Test of an MD-500 Helicopter with a Deployable Energy Absorber Concept

On December 2, 2009, a full scale crash test was successfully conducted of a MD-500 helicopter at the NASA Langley Research Center Landing and Impact Research Facility . The purpose of this test was to evaluate a novel composite honeycomb deployable energy absorbing (DEA) concept for attenuation of structural and crew loads during helicopter crashes under realistic crash conditions. The DEA concept is an alternative to external airbags, and absorbs impact energy through crushing. In the test, the helicopter impacted the concrete surface with 11.83 m/s (38.8 ft/s) horizontal, 7.80 m/s (25.6 ft/s) vertical and 0.15 m/s (0.5 ft/s) lateral velocities; corresponding to a resultant velocity of 14.2 m/s (46.5 ft/s). The airframe and skid gear were instrumented with accelerometers and strain gages to determine structural integrity and load attenuation, while the skin of the airframe was covered with targets for use by photogrammetry to record gross vehicle motion before, during, and after the impact. Along with the collection of airframe data, one Hybrid III 50th percentile anthropomorphic test device (ATD), two Hybrid II 50th percentile ATDs and a specialized human surrogate torso model (HSTM) occupant were seated in the airframe and instrumented for the collection of occupant loads. Resultant occupant data showed that by using the DEA, the loads on the Hybrid II and Hybrid III ATDs were in the Low Risk regime for the injury criteria, while structural data showed the airframe retained its structural integrity post crash. Preliminary results show that the DEA is a viable concept for the attenuation of impact loads.

Littell, Justin D.↗
NASA NTRS1992

Advanced wing design survivability testing and results

Composite wings on current operational aircraft are conservatively designed to account for stress/strain concentrations, and to assure specified damage tolerance. The technology that can lead to improved composite wing structures and associated structural efficiency is to increase design ultimate strain levels beyond their current limit of 3500 to 4000 micro-in/in to 6000 micro-in/in without sacrificing structural integrity, durability, damage tolerance, or survivability. Grumman, under the sponsorship of the Naval Air Development Center (NADC), has developed a high-strain composite wing design for a subsonic aircraft wing using novel and innovative design concepts and manufacturing methods, while maintaining a state-of-the-art fiber/resin system. The current advanced wing design effort addressed a tactical subsonic aircraft wing using previously developed, high-strain wing design concepts in conjunction with newer/emerging fiber and polymer matrix composite (PMC) materials to achieve the same goals, while reducing complexity. Two categories of advanced PMC materials were evaluated: toughened thermosets; and engineered thermoplastics. Advanced PMC materials offer the technological opportunity to take maximum advantage of improved material properties, physical characteristics, and tailorability to increase performance and survivability over current composite structure. Damage tolerance and survivability to various threats, in addition to structural integrity and durability, were key technical issues addressed during this study, and evaluated through test. This paper focuses on the live-fire testing, and the results performed to experimentally evaluate the survivability of the advanced wing design.

Bruno, J.↗
NASA NTRS1985

Thermal stress cycling of GaAs solar cells

A thermal cycling experiment was performed on GaAs solar cells to establish the electrical and structural integrity of these cells under the temperature conditions of a simulated low-Earth orbit of 3-year duration. Thirty single junction GaAs cells were obtained and tests were performed to establish the beginning-of-life characteristics of these cells. The tests consisted of cell I-V power output curves, from which were obtained short-circuit current, open circuit voltage, fill factor, and cell efficiency, and optical micrographs, spectral response, and ion microprobe mass analysis (IMMA) depth profiles on both the front surfaces and the front metallic contacts of the cells. Following 5,000 thermal cycles, the performance of the cells was reexamined in addition to any factors which might contribute to performance degradation. It is established that, after 5,000 thermal cycles, the cells retain their power output with no loss of structural integrity or change in physical appearance.

Janousek, B. K.↗
NASA NTRS1987

STA-2A NDT testing

The nondestructive testing (NDT) on the Space Shuttle Solid Rocket Booster (SRB) filament wound case (FWC) short stact structural test articles 2 (STA-2A) during test of phases 1B-9C is described. The primary objective of this testing was to verify the structural integrity of the SRB-FWC for critical design loads. Another objective was to quantify the effect of load distributions in the aft skirt. The NDT objectives were to determine the acoustic emission characteristics of the FWC-SRB and to identify possible design deficiencies or defect growth. The results from the posttest inspection of the samples shows the depth measurements taken were accurate until exceeding .260 inches thickness. The data then show that pulse echo measurements exceeded actual part thickness by 10 to 14 percent. The mapping of forward boundaries of delaminations proved to be within the tolerance of the equipment. Using the ZIP probe, the maximum difference between the pulse echo boundary and the visual boundary was expected to be no greater than one half the diameter of the probe. The NDT performance on STA-2A shows how NDT can be used to assist design engineering in evaluating the structural integrity of composite test articles.

Lewis, T. J.↗
NASA NTRS2009

Improved Method of Design for Folding Inflatable Shells

An improved method of designing complexly shaped inflatable shells to be assembled from gores was conceived for original application to the inflatable outer shell of a developmental habitable spacecraft module having a cylindrical mid-length section with toroidal end caps. The method is also applicable to inflatable shells of various shapes for terrestrial use. The method addresses problems associated with the assembly, folding, transport, and deployment of inflatable shells that may comprise multiple layers and have complex shapes that can include such doubly curved surfaces as toroids and spheres. One particularly difficult problem is that of mathematically defining fold lines on a gore pattern in a double- curvature region. Moreover, because the fold lines in a double-curvature region tend to be curved, there is a practical problem of how to implement the folds. Another problem is that of modifying the basic gore shapes and sizes for the various layers so that when they are folded as part of the integral structure, they do not mechanically interfere with each other at the fold lines. Heretofore, it has been a common practice to design an inflatable shell to be assembled in the deployed configuration, without regard for the need to fold it into compact form. Typically, the result has been that folding has been a difficult, time-consuming process resulting in a An improved method of designing complexly shaped inflatable shells to be assembled from gores was conceived for original application to the inflatable outer shell of a developmental habitable spacecraft module having a cylindrical mid-length section with toroidal end caps. The method is also applicable to inflatable shells of various shapes for terrestrial use. The method addresses problems associated with the assembly, folding, transport, and deployment of inflatable shells that may comprise multiple layers and have complex shapes that can include such doubly curved surfaces as toroids and spheres. One particularly difficult problem is that of mathematically defining fold lines on a gore pattern in a double- curvature region. Moreover, because the fold lines in a double-curvature region tend to be curved, there is a practical problem of how to implement the folds. Another problem is that of modifying the basic gore shapes and sizes for the various layers so that when they are folded as part of the integral structure, they do not mechanically interfere with each other at the fold lines. Heretofore, it has been a common practice to design an inflatable shell to be assembled in the deployed configuration, without regard for the need to fold it into compact form. Typically, the result has been that folding has been a difficult, time-consuming process resulting in a

Johnson, Christopher J.↗
NASA NTRS1978

Complementary DMOS-VMOS integrated circuit structure

A high speed CMOS formed on a single semiconductor substrate includes a DMOS having an asymmetric channel and a VMOS with a relatively short channel length. The short channel length of the VMOS is achieved by forming a double diffusion along one edge of a V groove, or ion implanting boron into the apex of the V groove and diffusing a single layer to a relatively deep depth along both edges of the groove.

Jhabvala, M. O.↗