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Little, S. A.

Publications and source records attributed to Little, S. A..

13 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

The role of the Long Duration Exposure Facility in the design of the Space Station Freedom

The Long Duration Exposure Facility (LDEF) satellite retrieved this year by the U.S. Space Shuttle offers spacecraft designers an unprecedented opportunity to examine synergistic, long-term space environmental effects on systems and materials. This paper discusses the strategy for data development and the role its implementation will play in the design of the Space Station Freedom. Examples are provided from three key areas (environments definition, protection of external surfaces, and verification of system components) to illustrate LDEF's potential contribution.

Little, S. A.↗
NASA NTRS1986

Analyses of spacecraft polymeric materials

Partial analytical characterizations are made by four different techniques of three polymeric materials used in conjunction with the Space Telescope for samples flown on mission STS-8. The polymers were Tedlar, Kapton H, and Kapton F. The surfaces of the three polymers were attacked and oxidized by atomic oxygen, and fluorine is lost from the surface of Kapton F, largely due to displacement by atomic oxygen.

Worley, S. D.↗
NASA NTRS1985

Orbital atomic oxygen effects on thermal control and optical materials - STS-8 results

The effects of exposing 23 specimens of optical and thermal control materials to space at 120 km altitude for over 40 hrs during the STS-8 mission are discussed. Ten samples of paint targeted for the Space Telescope (ST) and the Tethered Satellite were exposed, and included polyurethane, oxide, silicone, and glossy black and white samples which were scanned for alterations in the optical properties after being retrieved. Nine mirror-type materials were also investigated, along with silver specimens typical of solar cell interconnects. The oxygen flow at the orbital altitude was 3.5 x 10 to the 20th atoms/cu cm. The exposures caused no degradation of the magnesium fluoride mirror coatings, while the Kapton coating for the ST solar cell panels showed evidence of losing thickness. The Ag solar cell contacts will require coatings to extend their lifetimes. Overcoatings were also proven necessary for inhibiting degradation of painted surfaces.

Whitaker, A. F.↗
NASA NTRS1985

Protective coatings for atomic oxygen susceptible spacecraft materials - STS-41G results

Sixteen materials consisting of metallizations, silicones, and FEP Teflon were applied as protective coatings to selected spacecraft material surfaces and exposed on STS-41G to the LEO atomic oxygen environment. Evaluations of their protective effectiveness were made through assessing their mass loss/gain characteristics, maintenance of base material optical properties, and imperviousness to atomic oxygen attack. Generally, all coatings provided some degree of protection for the underlying material. In some cases the overcoat appeared to be too thin thereby providing inadequate protection.

Whitaker, A. F.↗
NASA NTRS1985

Reaction of metals in lower earth orbit during Space Shuttle flight 41-G

The effects of ambient space environment on metals were studied by exposing specimens of Cu, Ag, Au, Ni, Cr, Al, Pt, and Pd on flight 41-G (STS-17). Data obtained by ellipsometry (ELL), Rutherford backscattering (RBS), and proton-induced X-ray emission (PIXE) before and after flight are summarized. Although the effects of space environment were most pronounced for silver, there were significant changes in the surface properties of the majority of the other metals. The surface optical constants proved to be the most sensitive measure of surface changes. These changes are attributed to the interaction of the metals with atomic oxygen.

Fromhold, A. T., Jr.↗
NASA NTRS1983

Silicon solar cell characterization at low temperatures and low illumination as a function of particulate irradiation

Various configurations of back surface reflector silicon solar cells including small (2 x 2) cm and large (approx. 6 x 6) cm cells with conventional and wraparound contacts were subjected to 1 MeV electron irradiation and characterized under both Earth orbital and deep space conditions of temperatures and illuminations. Current-Voltage (I-V) data were generated from +65 C to -150 C and at incident illuminations from 135.3 mW/sq cm to 5.4 mW/sq cm for these cells. Degradation in cell performance which is manifested only under deep space conditions is emphasized. In addition, the effect of particle irradiation on the high temperature and high intensity and low temperature and low intensity performance of the cells is described. The cells with wraparound contacts were found to have lower efficiencies at Earth orbital conditions than the cells with conventional contacts.

Whitaker, A. F.↗
NASA NTRS1981

Characterization of ASEC BSR 2 ohm-cm silicon solar cells with dielectric wraparound contacts as a function of temperature and intensity

Twenty high performance BSR 2 ohm-cm silicon solar cells manufactured by ASEC were evaluated at 1 AU conditions and at low temperature and low intensities representative of deep space. These cells showed evidence of series resistance of 1 AU conditions and approximately 50% had reduced power outputs under deep space conditions. Average efficiency of these cells was 12.4% of 1 AU conditions of 1 SC/+25 C.

Whitaker, A. F.↗
NASA NTRS1981

Performance of candidate SEPS solar cells as a function of low temperature and low intensity exposure and 1 MeV electron irradiation

The behavior of 144 high-performance shallow-junction silicon solar cells under conditions of low temperature and intensity was examined. The cells represented nine combinations of thickness, base resistivity, front surface texture, and rear surface treatment. At least 16 cells of each type were individually tested both as active elements under light levels between 0.04 and 1.0 solar constant and in the dark as passive rectifiers under external forward bias. One cell type was also irradiated with 1 MeV electrons up to 2.7 x 10 to the 15th e/sq cm. The inferior cells demonstrated high ohmic and/or non-ohmic shunting. No series resistance or Schottky barrier effects were observed. Fluences beyond 10 to the 13th e/sq cm lowered cell current, probably by increasing volume recombination.

Whitaker, A. F.↗
NASA NTRS1980

Characterization of three types of silicon solar cells for SEPS Deep Space Mission. Volume 3: Current-voltage characteristics of spectrolab sculptured BSR/P+ (K7), BSR/P+ (K6.5) and BSR (K4.5) cells as a function of temperature and intensity

Three types of high performance silicon solar cells, sculptured BSR/P+(K7), BSR/P+(K6.5) and BSR(K4.5) manufactured by Spectrolab were evaluated for their low temperature and low intensity performance. Sixteen cells of each type were subjected to 11 temperatures and 9 intensities. The sculptured BSR/P+(K7) cells provided the greatest maximum power output both at 1 AU and at LTLI conditions. The average efficiencies of this cell were 14.4 percent at 1 SC/+25 deg C and 18.5 percent at 0.086 SC/-100 deg C.

Whitaker, A. F.↗
NASA NTRS1980

Characterization of three types of silicon solar cells for SEPS deep-space missions. Volume 2: Current voltage characteristics of Solarex textured P(+)8 to 10 mil, planar P(+)8 to 10 mil and planar P(+)2 mil cells as a function of temperature and intensity

Three types of high performance silicon solar cells, textured P(+)8 to 10 mil, planar P(+)8 to 10 mil and planar P(+)2 mil were evaluated for their low temperature and low intensity (LTLI) performance. Sixteen cells of each type were subjected to 11 temperatures and 9 intensities. The textured P(+)8 to 10 mil cells provided the best performance both at 1 astronomical unit and at LTLI conditions. The average efficiencies of this cell were 14.5 percent at 1 solar constant/+25 C and 18.7 percent at 0.086 solar constant/-100 C.

Whitaker, A. F.↗
NASA NTRS1979

Characterization of three types of silicon solar cells for SEPS deep space missions. Volume 1: Current-voltage characteristics of OCLI BSF/BSR 10 ohm-cm, and BSR 2 ohm-cm cells as a function of temperature and intensity

Three types of high performance silicon solar cells, BSF/BSR 10 ohm-cm, BSR 10 ohm-cm, and BSR 2 ohm-cm, were evaluated for their low temperature and low intensity performance. Sixteen cells of each type were subjected to ten temperatures and nine intensities. The BSF/BSR 10 ohm-cm cells provided the best performance at 1 solar constant and +25 C with an efficiency of 14.1% while the BSR 2 ohm-cm cells had the highest low temperature and low intensity performance with an efficiency of 22.2% at 0.04 solar constant and -170 C and the most consistent cell-to-cell characteristics.

Whitaker, A. F.↗
NASA NTRS1978

Evaluation of materials for high performance solar arrays

A program has been underway to evaluate materials for advanced solar arrays which are required to provide power to weight ratios up to 100 W/kg. Severe mission environments together with the lack of knowledge of space environmental materials degradation rates require the generation of irradiation and outgassing engineering data for use in the initial design phase of the flight solar arrays. Therefore, approximately 25 candidate array materials were subjected to selected mission environments of vacuum, UV, and particle irradiation, and their mechanical and/or optical properties were determined where appropriate.

Whitaker, A. F.↗