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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

LEO spacecraft leakage current and discharging phenomena - TRW LDEF SP-HVDE (space plasma-high voltage drainage experiment)

Two identical SP-HVDE trays were flown in the NASA 5.75-year LDEF (Long Duration Exposure Facility), one near the leading edge and the other near the trailing edge, in the LEO (low earth orbit) environment. Each experiment tray consisted of six assemblies with each made of Kapton dielectric samples of varying thicknesses (i.e., 2 mils, 3 mils, and 5 mils) biased under +/- 300 V, +/- 500 V, and +/- 1000 V. The objectives have been successfully achieved by measuring the first post-flight long-term (i.e. roughly 8-month experiment) average leakage current through 95 percent measurable coulombmeters and surface materials.

Yaung, J. Y.↗
NASA NTRS1992

High performance polymers and polymer matrix composites for spacecraft structural applications

A program implemented by NASA Langley Research Center to develop and evaluate new polymers and polymer matrix composites for spacecraft structural applications is examined. Various polymeric films, moldings, and adhesives are evaluated for resistance to atomic oxygen and high energy electron and UV radiation. Thin films from the poly(arylene ether)s containing phenylphosphine oxide groups and the siloxane-epoxies exhibited minor weight loss compared to Kapton polyimide after exposure. Large doses (greater than 10 exp 9 rads) of electron radiation, simulating 30 yr of exposure in GEO, are found to alter the chemical structure of epoxies by both chain scission and cross-linking. The thermal cycling representative of both LEO and GEO environments can cause microcracking in composites which can in turn affect the dimensional stability and produce mechanical property reductions. The processing and fabrication issues associated with precision composite spacecraft components are also addressed.

Bowles, D. E.↗
NASA NTRS1992

Changes in oxidation state of chromium during LDEF exposure

The solar collector used for the McDonnell-Douglas Cascade Variable Heat Pipe, Experiment A0076 (Michael Grote - Principal Investigator) was finished with black chromium plating as a thermal control coating. The coating is metallic for low emittance, and is finely microcrystalline to a dimension which yields its high absorptivity. An underplate of nickel was applied to the aluminum absorber plate in order to achieve optimal absorptance characteristics from the black chromium plate surface. Experiment A0076 was located at tray position F9, receiving a projected 8.7 x 10 exp 21 atomic oxygen atoms/sq cm and 11,200 ESH solar radiation. During retrieval, it was observed that the aluminized kapton thermal blankets covering most of the tray were severely eroded by atomic oxygen, and that a 'flap' of aluminum foil was overlaying a roughly triangular shaped portion of the absorber panel. The aluminum foil 'flap' was lost sometime between the Long Duration Exposure Facility (LDEF) retrieval and deintegration. At deintegration, the black chromium was observed to have discolored where it had been covered by the foil 'flap'. A summary of the investigation into the cause of the discoloration is presented.

Golden, Johnny L.↗
NASA NTRS1992

Erosion rates for polymers measured on LDEF

The summary and viewgraphs of work presented at the Long Duration Exposure Facility (LDEF) materials workshop are given. Experimental data for erosion depths and rates for polymers measured on LDEF are given. In general, agreement is reasonably good between erosion rates from the University of Alabama in Huntsville (UAH) LDEF experiment and prior data obtained at much lower mission fluences. Agreement is particularly satisfying in the case of Kapton where the prior data base is large. In spite of the known presence of silicaceous contamination on LDEF surfaces, the erosion rates of the highly erodible materials are hardly affected, if at all. Graphs showing changes in optical properties (reflectance and transmittance) of metal films are included.

Gregory, John C.↗
NASA NTRS1992

The use of plasma ashers and Monte Carlo modeling for the projection of atomic oxygen durability of protected polymers in low Earth orbit

The results of ground laboratory and in-space exposure of polymeric materials to atomic oxygen has enabled the development of a Monte Carlo computational model which simulates the oxidation processes of both environments. The cost effective projection of long-term low-Earth-orbital durability of protected polymeric materials such as SiO(x)-coated polyimide Kapton photovoltaic array blankets will require ground-based testing to assure power system reliability. Although silicon dioxide thin film protective coatings can greatly extend the useful life of polymeric materials in ground-based testing, the projection of in-space durability based on these results can be made more reliable through the use of modeling which simulates the mechanistic properties of atomic oxygen interaction, and replicates test results in both environments. Techniques to project long-term performance of protected materials, such as the Space Station Freedom solar array blankets, are developed based on ground laboratory experiments, in-space experiments, and computational modeling.

Banks, Bruce A.↗
NASA NTRS1992

Four space application material coatings on the long-duration exposure flight (LDEF)

Four material coatings of different thickness were flown on the LDEF to determine their ability to perform in the harsh space environment. The coatings, located in the ram direction of the spacecraft, were exposed for 10 months to the low-Earth orbit (LEO) environment experienced by the LDEF at an orbit of 260 nautical miles. They consisted of indium oxide (In2O3), silicon oxide (SiO(x)), clear RTV silicone, and silicone with silicate-treated zinc oxide (ZnO). These coatings were flown to assess their behavior when exposed to atomic oxygen and to confirm their good radiative properties, stability, electrical conductivity, and resistance to UV exposure. The flown samples were checked and compared with the reference unflown samples using high-magnification optical inspection, ESCA analysis, weight changes and dimensional changes. These comparisons indicated the following: The 1000 A SiO(x) coating eroded uniformly, with minor changes in its radiative properties. The 100 A of In2O3 coating eroded completely down to the Kapton backing, with resultant losses of reflectance. The RTV-615 showed erosion, with carbon (C) content losses, while the Si remained constant, with a doubling of the oxygen (O) concentration. The RTV-615 silicone with K2SiO3-treated ZnO changed from flat to glossy white in appearance. It lost C, was etched, and increased its O content. The upper layers showed no remaining Zn or K. Losses of reflectance occurred within certain wavelength bands. It was not possible to evaluate the experimental oxygen reaction rate using the calculated atomic oxygen fluence of 2.6 x 10(exp 20) atoms/cm(exp 2) for the exposure of these coatings during the flight. The bakeout of the coatings was not carried out prior to the flight. Hence, the coating weight and dimensional losses included losses by outgassing products.

Scialdone, John J.↗
NASA NTRS1993

Oxygen plasma resistant phosphine oxide containing imide/arylene copolymers

A series of oxygen plasma resistant imide/arylene ether copolymers were prepared by reacting anhydride-terminated poly(amide acids) and amine-terminated polyarylene ethers containing phosphine oxide units. Inherent viscosities for these copolymers ranged from 0.42 to 0.80 dL/g. After curing, the resulting copolymers had glass transition temperatures ranging from 224 C to 228 C. Solution cast films of the block copolymers were tough and flexible with tensile strength, tensile moduli, and elongation at break up to 16.1 ksi, 439 ksi, and 23 percent, respectively at 25 C and 9.1 ksi, 308 ksi and 97 percent, respectively at 150 C. The copolymers show a significant improvement in resistance to oxygen plasma when compared to the commercial polyimide Kapton. The imide/arylene ether copolymers containing phosphine oxide units are suitable as coatings, films, adhesives, and composite matrices.

Jensen, Brian J.↗
NASA NTRS1992

Recommended practices for in-space and ground laboratory. Atomic oxygen exposure and analysis

A detailed guide to testing materials for atomic oxygen durability in earth orbit environments is presented. The steps covered include sample preparation, including masking of the sample, dehydration, weighing, and handling; effective fluence prediction, including the use of witness samples (notably Kapton); plasma facility and operational considerations, involving such matters as avoidance of silicone contamination, the use of continuous versus incremental ashing, and temperature of operation; and erosion yield measurement, with calculation methods and protective coating performance indices provided.

Banks, Bruce↗
NASA NTRS1993

Low Earth orbital atomic oxygen environmental simulation facility for space materials evaluation

Simulation of low Earth orbit atomic oxygen for accelerated exposure in ground-based facilities is necessary for the durability evaluation of space power system component materials for Space Station Freedom (SSF) and future missions. A facility developed at the National Aeronautics and Space Administrations's (NASA) Lewis Research Center provides accelerated rates of exposure to a directed or scattered oxygen beam, vacuum ultraviolet (VUV) radiation, and offers in-situ optical characterization. The facility utilizes an electron-cyclotron resonance (ECR) plasma source to generate a low energy oxygen beam. Total hemispherical spectral reflectance of samples can be measured in situ over the wavelength range of 250 to 2500 nm. Deuterium lamps provide VUV radiation intensity levels in the 115 to 200 nm range of three to five equivalent suns. Retarding potential analyses show distributed ion energies below 30 electron volts (eV) for the operating conditions most suited for high flux, low energy testing. Peak ion energies are below the sputter threshold energy (approximately 30 eV) of the protective coatings on polymers that are evaluated in the facility, thus allowing long duration exposure without sputter erosion. Neutral species are expected to be at thermal energies of approximately .04 eV to .1 eV. The maximum effective flux level based on polyimide Kapton mass loss is 4.4 x 10 exp 6 atoms/((sq. cm)*s), thus providing a highly accelerated testing capability.

Stidham, Curtis R.↗
NASA NTRS1990

Electrical power system WP-04

Viewgraphs on Space Station Freedom Electrical Power System (EPS) WP-40 are presented. Topics covered include: key EPS technical requirements; photovoltaic power module systems; solar array assembly; blanket containment box and box positioning subassemblies; solar cell; bypass diode assembly; Kapton with atomic oxygen resistant coating; sequential shunt unit; gimbal assembly; energy storage subsystem; thermal control subsystem; direct current switching unit; integrated equipment assembly; PV cargo element; PMAD system; and PMC and AC architecture.

Nored, Donald L.↗
NASA NTRS1993

An XPS study of space-exposed polyimide film

X-ray photoelectron spectroscopy was used to assess changes induced in the surface chemistry of Kapton H (Du Pont Trademark) polyimide strips exposed to the low Earth orbit environment at the space-end of the LDEF satellite on Experiment A0133. Results from flight specimens are compared to material cut from the same lot and stored at room temperature under standard atmospheric conditions. One notable difference was a nearly two-fold increase in surface oxygen (atom-percent composition) for specimens exposed to the direct space environment as compared to controls. In addition, space exposed specimens contained distinct silicon peaks (2p 103.2 eV and 2s 154.2 eV) in their spectra. These peaks were absent in control spectra. It is likely that the increase in oxygen is associated with the silicon. This is in agreement with reports of widespread silicon contamination throughout the LDEF satellite.

Lee, Myung↗
NASA NTRS1993

LDEF Space Plasma-High Voltage Drainage Experiment post-flight results

The Space Plasma-High Voltage Drainage Experiment (SP-HVDE) was comprised of two identical experimental trays. With one tray located on the leading (ram facing, B10) edge and the other located on the trailing (wake facing, D4) edge of the Long Duration Exposure Facility (LDEF), it was possible to directly compare the effects of ram and wake spacecraft environments on charged dielectric materials. Six arrays of Kapton dielectric samples of 2 mil, 3 mil, and 5 mil thicknesses maintained at +/- 300, +/- 500, and +/- 1000 voltage bias formed the experimental matrix of each tray. In addition, each tray carried two solar cell strings, one biased at +300 volts and the other at -300 volts, to study current leakage from High Voltage Solar Arrays (HVSA). The SP-HVDE provides the first direct, long-term, in-flight measurements of average leakage current through dielectric materials under electric stress. The experiment also yields information on the long term stability of the bulk dielectric properties of such materials. Data and findings of the SP-HVDE are an extension of those from shorter term flight experiments such as the PIX-1 (Plasma Interaction Experiment) and PIX-2 and are therefore valuable in the design and evaluation of long-lived space systems with high voltage systems exposed to the low earth orbital environment. A summary of the SP-HVDE post flight analysis final report delivered to the LDEF Project Office under contract to the National Aeronautics and Space Administration is presented.

Yaung, J. Y.↗
NASA NTRS1992

Reactions of atomic oxygen /O(3P)/ with polymer films

The reactions of polymer films with oxygen atoms are reviewed focusing on laboratory tests on polybutadienes with different amount of 1,4 or 1,2 double bonds and their polyalkenamer homologues, polyimide (Kapton), and a series of polyolefines with increasing fluorine content. It is found that etch rates increase with decrease in -CH=CH- unsaturation, starting with 1,4 -polybutadiene and reaching the maximum rate with polyethylene or ethylene-propylene rubber. IN polybutadienes with both 1,4 and 1,2 double bonds, the rate of O(3P)-induced etching is lower the higher the 1,2 content. The reactions are confined to the polymer surface.

Golub, Morton A.↗
NASA NTRS1993

Plasma chamber testing of APSA coupons for the SAMPIE flight experiment

Different blanket materials and mounting techniques have been used to build 12 Advanced Photovoltaic Solar Array cell coupons for NASA's Solar Array Module Plasma Interactions Experiment. Ground testing of these coupons in a plasma chamber revealed significant differences among them in plasma current collection; while the Kapton-H coupon exhibited current collection consistent with the exposed interconnects, the other two coupon types tested experienced anomalously large collection currents. This may be due to enhanced plasma sheaths supported by the weakly conducting C and Ge employed in these coupons.

Hillard, G. B.↗
NASA NTRS1990

Polyimides from a methylene-bridged dianhydride

High-molecular weight, high-temperature, highly optically transparent films suitable for electronic and aerospace applications were prepared based on a novel methylene-bridged dianhydride 3,3-prime bis(3,4-dicarboxyphenoxy) diphenylmethane dianhydride (PDMDA). All films had lower dielectric constants and significantly higher optical transparency than the commercial Kapton H film, with air-cured films having slightly higher dielectric constants and lower optical transparency than vacuum films, due to oxidative cross-linking.

Boston, Harold G.↗
NASA NTRS1992

The evolution of procurement and assurance methods used to proof an advanced space material

A development history and current performance evaluation is presented for a Kapton polyimide for the Space Station Freedom. Analyses of results obtained for this class of materials by the Long Duration Exposure Facility led to major revisions of procurement specifications and test requirements for this material. Attention is given to the use of oxygen plasma etching and blocking, as well as the evolution of test methodologies due to preproduction test data evaluations and the relationship between tests and product-improvement cycles.

Berendt, Marjorie↗
NASA NTRS1993

Scanning Tunneling Microscopy analysis of space-exposed polymer films

The characterization of the surface of selected space-exposed polymer films by Scanning Tunneling Microscopy (STM) is reported. Principles of STM, an emerging new technique for materials analysis, are reviewed. The analysis of several films which received up to 5.8 years of low Earth orbital (LEO) exposure onboard the NASA Long Duration Exposure Facility (LDEF) is discussed. Specimens included FEP Teflon thermal blanket material, Kapton film, and several experimental polymer films. Ultraviolet and atomic oxygen-induced crazing and erosion are described. The intent of this paper is to demonstrate how STM is enhancing the understanding of LEO space environmental effects on polymer films.

Kalil, Carol R.↗
NASA NTRS1994

Double-Square-Loop Triband Frequency-Selective Microwave Reflector

Double-square-loop antenna elements arrayed on dielectric panel. Dichroic microwave reflector consisting of planar square array of double-square-loop copper elements on thin sheet of Kapton (or equivalent) polyimide supported by Kevlar (or equivalent) aromatic polyamid honeycomb sandwich panel. Array and panel designed to reflect most of incident electromagnetic radiation of frequencies between 7.2 and 8.4 GHz (in X band) and to transmit most of that at 2.3 GHz (in S Band) and 13.8 GHz {in K(sub u) band}.

Wu, Te-Kao↗