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At least 289 records · Page 16

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NASA NTRS1980

Electromagnetic fields produced by simulated spacecraft discharges

The initial phase of a broader, more complete program for the characterization of electrical breakdowns on spacecraft insulating materials is described which consisted of the development of a discharge simulator and characterization facility and the performance of a limited number of discharge measurements to verify the operation of the laboratory setup and to provide preliminary discharge transient field data. A preliminary model of the electromagnetic characteristics of the discharge was developed. It is based upon the "blow off" current model of discharges, with the underlying assumption of a propagating discharge. The laboratory test facility and discharge characterization instrumentation are discussed and the general results of the "quick look" tests are described on quartz solar reflectors aluminized Kapton and silver coated Teflon are described.

Nonevicz, J. E.↗

NASA NTRS1981

Solar cell modules for plasma interaction evaluation

A plasma interaction analysis in support of the solar electric propulsion subsystem examined the effects of a large high voltage solar array interacting with an ion thruster produced plasma. Two solar array test modules consisting of 36 large area wraparound contact solar cells welded to a flexible Kapton integrated circuit substrate were abricated. The modules contained certain features of the effects of insulation, din-holes, and bonding of the cell to the substrate and a ground plane. The possibility of a significant power loss occurring due to the collection of charged particles on the solar array interconnects was the focus of the research.

Source record↗

NASA NTRS1982

An investigation of the aerodynamic characteristics of a new general aviation airfoil in flight

A low speed airfoil, the GA(W)-2, - a 13% thickness to chord ratio airfoil was evaluated. The wing of a Beech Sundowner was modified at by adding balsa ribs and covered with aluminum skin, to alter the existing airfoil shape to that of the GA(W)-2 airfoil. The aircraft was flown in a flight test program that gathered wing surface pressures and wake data from which the lift drag, and pitching moment of the airfoil could be determined. After the base line performance of the airfoil was measured, the drag due to surface irregularities such as steps, rivets and surface waviness was determined. The potential reduction of drag through the use of surface coatings such as KAPTON was also investigated.

Gregorek, G. M.↗

NASA NTRS1982

Interaction between the SPS solar power satellite solar array and the magnetospheric plasma

The results of study to determine the effects of space plasmas on a large GaAs solar cell array using solar reflectors at a concentration ratio of two in geostationary orbit are summarized. It was concluded that the system could function in the GEO environment if certain design changes were implemented. These included conductive coatings on the solar cells, changing the reflector material from Kapton to a higher conductivity material, and oversizing the array to compensate for a 0.7% parasitic load due to losses from the ambient magnetospheric plasma. The operation of the solar powered earth orbit transfer vehicle (EOTV) was also examined and it was concluded that LEO servere arcing would take place on all high voltage negative portions of the array. The parasitic load loss at LEO was estimated at 3%. Operation of a high voltage array at LEO represents a major problem. Charge exchange ion feedback from argon ion thrusters located near the EOTV solar array was also examined and all problems found were believed to be solvable by the placement of protective ground screens.

Freeman, J. W.↗

NASA NTRS1982

Phenomenology of surface arcs on spacecraft dielectric materials

For electron beam incidence on large specimens of Kapton thermal blanket material, surface arc discharges are shown to cause damage consisting of punchthrough holes which act as focal points for other types of damage, including subsurface tunnels, blowout holes and surface breakup. Under electron bombardment, dielectric sheet specimens separated by a gap are shown to discharge simultaneously. Teflon specimens which have been brushed or rubbed are shown to exhibit directional guidance of discharge arcs, and this phenomenon has been used to generate straight arcs whose velocities have been measured optically.

Balmain, K. G.↗

NASA NTRS1983

Results of thermal environment measurements on the thermal cannister experiment and get away special enclosure

Because the OSS-1 pallet contained a variety of instruments with irregular surface geometry and properties which limited predictability, the total absorbed flux on thermal canister radiators was measured to determine heat rejection capability. The instrumentation and sensor cup design and locations for the thermal canister experiment are illustrated. Graphs show flux sensor history in hot and coal orbits. Kapton erosion is also considered. Results show that the flux levels measured in all STS attitudes are higher than predictions. In cold and moderate attitudes, flight results are a factor of two to three higher than predicts. In hot attitude, much better agreement occurred. It is concluded that in cold or moderate attitudes other sources may be contributing to added inputs (albedo, Earth shine, shuttle background). In hot attitude, smaller differences could be attributed to coatings assumptions or calculation uncertainty.

Ollendorf, S.↗

NASA NTRS1982

Development of technologies for welding interconnects to fifty-micron thick silicon solar cells

A program was conducted to develop technologies for welding interconnects to 50 microns thick, 2 by 2 cm solar cells. The cells were characterized with respect to electrical performance, cell thickness, silver contact thickness, contact waviness, bowing, and fracture strength. Weld schedules were independently developed for each of the three cell types and were coincidentally identical. Thermal shock tests (100 cycles from 100 C to -180 C) were performed on 16 cell coupons for each cell type without any weld joint failures or electrical degradation. Three 48 cell modules (one for each cell type) were assembled with 50 microns thick cells, frosted fused silica covers, silver clad Invar interconnectors, and Kapton substrates.

Patterson, R. E.↗

NASA NTRS1983

Performance of a quantitative study of instability-related delamination growth

An experimental program was conducted to quantify instability-induced imbedded delamination growth. Static tests on double cantilever beam (DCB) specimens yielded the critical mode 1 strain energy release rate (G sub 1 C) for T300/5208 graphite/epoxy. Static tests on mixed mode cracked lap shear (CLS) specimens, and a nonlinear finite element analysis (NFEA) of the CLS specimen to separate mode 1 and mode 2 effects, yielded the critical mode 2 strain energy release rate (G sub 2 C) for T300/5208. Constant amplitude fatigue tests on DCB and CLS specimens, along with the NFEA results on CLS specimens, quantified mode 1 and mode 2 contributions to delamination growth rate. Fatigue tests were conducted at a frequency (omega) of 10 Hertz, maintaining the minimum to maximum cyclic load ratio (R) at 0.05. Static compression and constant amplitude compression fatigue tests were also conducted on specimens with imbedded through the width (ITTW) delaminations. Kapton imbeddments were located below 3, 4 or 6 plies in a 64-ply laminate, during layup, to simulate ITTW delaminations.

Ramkumar, R. L.↗

NASA NTRS1983

Oxygen atom reaction with Shuttle materials at orbital altitudes - Data and experiment status

Significant surface characteristics changes have been noticed on materials that were exposed in the payload bay of the Space Shuttle Orbiter on the first four flights. The most notable change was mass loss of Kapton film used as a component of thermal blankets. This film exhibited as much as 35 percent mass loss on STS-3 and loss of material was noticed on all flights. Other changes consist of rapid aging of paints and oxidation of Torlon surfaces. A mechanism has been proposed for the effects described, which involves the interaction of these organic materials with atomic oxygen available at low earth orbital altitudes. Evidence derived from measurements made on Shuttle materials that supports this mechanism will be presented. Experiments planned for near-term Shuttle flights are being developed to obtain quantitative data on reaction rates.

Leger, L.↗

NASA NTRS1982

Potentials on large spacecraft in LEO

A system-oriented computer code is used to predict surface charging due to voltages generated within a satellite operating in the typical dense plasma environment of LEO. The use of this code is demonstrated by predicting the expansion of electric fields onto a kapton surface from a pinhole over a biased conductor in a LEO environment. The results are compared to a more-exact solution and experimental data.

Mandell, M. J.↗

NASA NTRS1982

Characteristics of RF resulting from dielectric discharges

This paper presents measurements of the electromagnetic radiation pulses and the replacement current pulses which result from the breakdown of Mylar and Kapton samples. The observed dependence of the characteristics of the replacement current pulse as a function of electron beam energy is discussed. The characteristics of the electromagnetic radiation pulses are also analyzed in the text of this paper. The source of the irradiating electrons is a monoenergetic electron beam whose energy was varied from 12.5 KeV to 25 KeV.

Leung, P.↗

NASA NTRS1983

Development of an improved protective cover/light block for multilayer insulation

The feasibility of using a scrim-reinforced, single metallized, 4-mil Tedlar film as a replacement for the Teflon coated Beta-cloth/single metallized 3-mil Kapton film presently used as the protective cover/light block for multilayer insulation (MLI) on the Orbiter, Spacelab, and other space applications was demonstrated. The proposed Tedlar concept is lighter and potentially lower in cost. Thermal analysis with the proper concept was much simpler than with the present system. Tests have already demonstrated that white Tedlar has low alpha (adsorption) degradation in space from U.V. The proposed concept was 4400 percent cheaper with nominal weight savings of 50 percent.

Thompson, L. M.↗

NASA NTRS1984

Neon transport in selected organic composites

An energy-dependent, perturbation expansion solution for heavy-ion transport in one dimension was used to calculate the dose from Ne-20 beams at incident kinetic energies of 350, 670, and 2000 MeV/amu onto selected organic composites. Transport coefficients, applicable to arbitrary ion beams over a broad range of energies, are presented. Polyethylene and Kapton were tested as constituents of multilayered shielding for spacecraft and astronauts.

Townsend, L. W.↗

NASA NTRS1984

Ion-beam-textured and coated surfaces experiment (S1003)

The objective of this LDEF experiment is to measure the effects of exposure to the shuttle launch and near Earth space environments on the optical properties of ion beam textured high absorptance solar thermal control surfaces, the optical and electrical properties of ion beam sputtered conductive solar thermal control surfaces, and the weight loss of ion beam deposited oxide polymer films. The various types of surfaces to be tested include six major categories: (1) ion beam textured surfaces suitable for space solar thermal (solar concentration) application; (2) painted and/or state of the art solar thermal surfaces; (3) ion beam sputtered conductive coatings for thermal and space charge control (e.g., indium-oxide coated metalized FEP Teflon); (4) ion beam sputtered conductive coated solar sail materials for space charge control and cooling through emittance; (5) micrometeoroid sensitive samples whose optical properties change only as a result of micrometeoroid impact; and (6) Kapton coated with oxide polymer films to minimize oxygen degradation at near Earth orbit altitudes.

Mirtich, M. J., Jr.↗

NASA NTRS1984

An atomic oxygen facility for studying polymer materials for spacecraft applications

A nozzle beam facility utilizing microwave discharge on a helium carrier gas seeded with oxygen to produce atomic oxygen fluxes of the order of 10 to the 15th power atoms/cu cm/sec is described. In addition, limited test results obtained from exposing a graphite/epoxy composite and Kapton (H) film are presented in terms of mass loss measurements and changes in surface morphology.

Tennyson, R. C.↗

NASA NTRS1983

Welding interconnects to 50-micron silicon solar cells

A program was conducted to develop technologies for welding interconnects to 50-micron thick, 2 by 2 cm solar cells obtained from three suppliers. The cells were characterized with respect to electrical performance, cell thickness, silver contact thickness, contact waviness, bowing, and fracture strength. Weld schedules were independently developed for each of the three cell types and were coincidentally identical. Thermal shock tests (100 cycles from 100 deg to -180 deg C) were performed on 16-cell coupons for each cell type without any weld joint failures or electrical degradation. Three 48-cell modules (one for each cell type) were assembled with 50-micron thick cells, frosted fused silica covers, silver clad Invar interconnectors, and Kapton substrates.

Patterson, R. E.↗

NASA NTRS1985

Mass spectra of neutral particles released during electrical breakdown of thin polymer films

A special type of time-of-flight mass spectrometer triggered from the breakdown event was developed to study the composition of the neutral particle flux released during the electrical breakdown of polymer films problem. Charge is fed onto a metal-backed polymer surface by a movable smooth platinum contact. A slowly increasing potential from a high-impedance source is applied to the contact until breakdown occurs. The breakdown characteristics is made similar to those produced by an electron beam charging system operating at similar potentials. The apparatus showed that intense instantaneous fluxes of neutral particles are released from the sites of breakdown events. For Teflon FEP films of 50 and 75 microns thickness the material released consists almost entirely of fluorocarbon fragments, some of them having masses greater than 350 atomic mass units amu, while the material released from a 50 micron Kapton film consists mainly of light hydrocarbons with masses at or below 44 amu, with additional carbon monoxide and carbon dioxide. The apparatus is modified to allow electron beam charging of the samples.

Kendall, B. R. F.↗

NASA NTRS1985

Electron yields from spacecraft materials

Photoyields and secondary electron emission (SEE) characteristics were determined under UHV conditions for a group of insulating materials used in spacecraft applications. The SEE studies were carried out with a pulsed primary beam while photoyields were obtained with a chopped photon beam from a Kr resonance source with major emission at 123.6 nm. This provides a photon flux close to that of the Lyman alpha in the space environment. Yields per incident photon are obtained relative to those from a freshly evaporated and air oxidized Al surface. Results are presented for Kapton, FEP Teflon, the borosilicate glass covering of a shuttle tile, and spacesuit outer fabric.

Yang, K.↗