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At least 127 records · Page 7

All sources NASA NTRS DOE OSTI

NASA NTRS1975

Determination of mechanical properties of polymer film materials

Five polymeric film materials, Tedlar, Teflon, Kapton H, Kapton F, and a fiberglass reinforced polyimide, PG-402, in thickness ranging from 0.002 to 0.005 inch, were tested over a temperature range of -195 to 200 C in the "machine" and transverse direction to determine: elastic modulus, Poisson's ratio, three percent offset yield stress, fracture stress, and strain to fracture. The elastic modulus, yield stress and fracture stress decreased with increasing temperature for all the materials while the fracture strain increased. Teflon and Tedlar had the greatest temperature dependence and PG-402 the least. At 200 C the Poisson ratio values ranged from 0.39 to 0.5; they diminished as the temperature decreased covering a range of 0.26 to 0.42 at -195 C. Shortening the gauge length from eight inches to one inch increased the strain to fracture and lowered the elastic modulus values.

Hughes, E. J.↗

NASA NTRS1977

The 200 watts/kilogram solar array conceptual approach study. Phase 2: Assessment report for proof-of-concept experiments and Halley's comet concentrator array

The activities associated with the fabrication, handling, and testing of 2-mil solar cell modules on a flexible substrate are demonstrated. It is shown that 2-mil solar cells can be reliably handled, welded, and bonded to a Kapton substrate. Flexible Invar interconnects can be used to interconnect individual cells to form modules. These solar cell modules can be temperature cycled, wrapped around a 10-inch diameter drum, and vibrated to the shuttle environment with no significant damage. A bonding technique was developed to physically join adjacent modules that is stronger than the Kapton, itself. Ultraviolet radiation tests were performed on RTV - silicone as a cell cover material - with very encouraging results.

Source record↗

NASA NTRS1978

Evaluation of glass resin coatings for solar cell applications

Using a variety of non-vacuum deposition techniques coatings were implemented on silicon solar cells and arrays of cells interconnected on Kapton substrates. The coatings provide both antireflection optical matching and environmental protection. Reflectance minima near 2% was achieved at a single wavelength in the visible. Reflectance averaging below 5% across the useful collection range was demonstrated. The coatings and methods of deposition were: (1) Ta2O5 spun, dipped or sprayed; (2) Ta2O5.SiO2 spun, dipped or sprayed; (3) GR908 (SiO2) spun, dipped, or sprayed. Total coating thickness were in the range of 18 microns to 25 microns. The coatings and processes are compatible with single cells or cells mounted on Kapton substrates.

Field, M. B.↗

NASA NTRS1978

High resolution masks for ion milling pores through substrates of biological interest

The feasibility was investigated of electrochemically oxidizing vapor deposited aluminum coatings to produce porous aluminum oxide coatings with submicron pore diameters and with straight channels normal to the substrate surface. Porous aluminum oxide coatings were produced from vapor deposited aluminum coatings on thin stainless steel (304), copper, Teflon (FEP) and Kapton substrates and also on pure aluminum substrates. Scanning electron microscope examination indicated that porous oxide coatings can be produced with straight channels, appropriate pore diameters and none or minimal intervening residual aluminum. The oxide coatings on the copper and Kapton substrates had the straightest channels and in general were superior to those fabricated on the other substrate materials. For oxide coatings fabricated at 600 V and 300 V, pore diameters were 0.4-0.6, and 0.3 micron with center-to-center spacing of 0.7-0.8, and 0.4 micron, respectively. Estimated direct labor and materials costs to prepare an oxide mask is anticipated to be about $4-$6 per square foot.

Donovan, S. S.↗

NASA NTRS1978

Measurements of material properties for solar cells

Measurements on two candidate materials for space flight are reported. The observed optical transmittance of aluminum films vapor deposited on fused quartz showed anomalously high transmittance thru 400 A and 600 A and showed an effective skin depth of 110 A in the latter part of the 1000 A thickness. KAPTON films are shown by their optical transmission spectra to have an energy gap for electron excitation of approximately 2.5 eV, which value depends on the thickness as manufactured. The resistance of KAPTON film to ionizing radiation is described by their optical spectra and their electron spin resonance spectra.

Castle, J. G., Jr.↗

NASA NTRS1979

Test results for electron beam charging of flexible insulators and composites

Flexible solar-array substrates, graphite-fiber/epoxy - aluminum honeycomb panels, and thin dielectric films were exposed to monoenergetic electron beams ranging in energy from 2 to 20 keV in the Lewis Research Center's geomagnetic-substorm-environment simulation facility to determine surface potentials, dc currents, and surface discharges. The four solar-array substrate samples consisted of Kapton sheet reinforced with fabrics of woven glass or carbon fibers. They represented different construction techniques that might be used to reduce the charge accumulation on the array back surface. Five honeycomb-panel samples were tested, two of which were representative of Voyager antenna materials and had either conductive or nonconductive painted surfaces. A third sample was of Navstar solar-array substrate material. The other two samples were of materials proposed for use on Intelsat V. All the honeycomb-panel samples had graphite-fiber/epoxy composite face sheets. The thin dielectric films were 2.54-micrometer-thick Mylar and 7.62-micrometer-thick Kapton.

Staskus, J. V.↗

NASA NTRS1978

Protection of solar collector materials from UV

Certain plastic films, such as KAPTON, are known to be stable with excellent long-term aging characteristics under intense uv radiation. Our recent measurements of the optical transmission spectra of KAPTON films show an absorption edge in the blue and are interpreted in terms of an electronic excitation mechanism. The application of this type of film as covering for solar collectors is discussed in regard to the protection this strong uv absorption offers to the materials underneath.

Castle, J. G., Jr.↗

NASA NTRS1980

High-temperature adhesives for bonding polyimide film

Experimental polyimide resins were developed and evaluated as potential high temperature adhesives for bonding Kapton polyimide film. Lap shear strengths of Kapton/Kapton bonds were obtained as a function of test temperature, adherend thickness, and long term aging at 575 K (575 F) in vacuum. Glass transition temperatures of the polyimide/"Kapton" bondlines were monitored by thermomechanical analysis.

St.clair, A. K.↗

NASA NTRS1981

Flaw criticality of circular disbond defects in compressive laminates

The compressive behavior of T300/5208 graphite-epoxy laminates containing circular delaminations was studied to determine the flaw criticality of two types of implanted defect, Kapton bag and Teflon film, on several laminate configurations. Defect size was varied. Results, presented in the form of residual strength curves, indicate that the Teflon film defect reduced strength more than the Kapton bad defect in 12-ply samples, but that two laminates (+ or - 45) sub 2s and (90/+ or - 45) sub s were insensitive to any implanted defect. A clear thickness effect was shown to exist for the (o/+ pr 45) sub ns laminate and was attributed to failure mode transition. The analytically predicted buckling loads show excellent agreement with experimental results and are useful in predicting failure mode transition.

Webster, J. D.↗

NASA NTRS1980

Dielectric discharge characteristics in a two-electron simulation environment

The results of a series of experiments in which flux levels representative of the space electron environment were used are presented and compared to the results of high flux tests. The simulation approach was to partition the space electron spectrum into two parts, those electrons which do not penetrate a material and therefore contribute to charging and those which completely penetrate the material. The nonpenetrating electrons were simulated using 25 keV electrons and the penetrating electrons by 350 keV electrons. The materials included in this investigation were Kapton, optical solar reflectors (OSRs), and a ground test satellite surface potential monitor which contained Kapton, astroquart, OSRs and teflon.

Treadaway, M.↗

NASA NTRS1981

Role of energetic particles in charging/discharging of spacecraft dielectrics

The role that energetic particles in the substorm plasma have on the charging and discharging of typical dielectric layers used on spacecraft was investigated using spectra and pitch angle distributions measured in situ on the SCATHA spacecraft prior to and during a few kilovolt differential charging event in eclipse conditions. The particle spectra was input to deposition codes that determine the dose rate as a function of depth in Kapton and Teflon layers used in an experiment on SCATHA. The calculated ambient dose rates of a few rads/sec throughout the bulk of the samples are sufficiently high that radiation damage levels are reached on the time scale of 1 year. Surface dose is a factor of 100 higher. Bulk conductivity profiles were obtained from the dose rates using empirical relationships. The radiation induced bulk conductivities calculated at the peak charging time are found to be smaller than the intrinsic dark conductivity range of solar conditioned Kapton but higher than the corresponding value for Teflon.

Reagan, J. B.↗

NASA NTRS1981

Dielectric surface discharges: Effects of combined low-energy and high-energy incident electrons

Dielectric surface discharges affected by the addition of high energy electrons at 5 pA/sq cm to a primary 20 keV, 10 nA/sq cm electron beam with the high energy broad spectrum particles coming from the beta decay of Strontium 90 are studied. Kapton exhibits significantly increased discharge strength, increased waiting time between discharges, and a decreased number of discharges per specimen before discharge cessation. Mylar exhibits similar but less pronounced effects, while Teflon is relatively unaffected. With Kapton and Mylar, the high energy electrons act in some way to delay the instant of discharge ignition so that more charge can be accumulated and hence released during discharge.

Balmain, K. G.↗

NASA NTRS1981

Design of an arc-free thermal blanket

The success of a multilayer thermal blanket in eliminating arcing is discussed. Arcing is eliminated by limiting the surface potential to well below the threshold level for discharge. This is achieved by enhancing the leakage current which results in conduction of the excess charge to the spacecraft structure. The thermal blanket consists of several layers of thermal control (space approved) materials, bonded together, with Kapton on the outside, arranged in such a way that when the outer surface is charged by electron irradiation, a strong electric field is set up on the Kapton layer resulting in a greatly improved conductivity. The basic properties of matter utilized in designing this blanket method of charge removal, and optimum thermo-optical properties are summarized.

Fellas, C. N.↗

NASA NTRS1980

satellite surface potential survey

Results of Kapton differential voltage charging of the satellite surface potential monitor Kapton samples are presented for the first 100 days of P78-2 operations. Daily charging occurrences are plotted in magnetic local time and L-shell (altitude and magnetic latitude) space as a function of magnetic activity. Most of the low level charging occurs well into the dawn local time sector whereas the highest voltage levels occur in the premidnight local time sector. The probabilities of differential charging are extremely dependent on the local time sector, the altitude (or L-shell) and of course, the magnetic activity.

Mizera, P. F.↗

NASA NTRS1983

Mass analysis of neutral particles and ions released during electrical breakdowns on spacecraft surfaces

A specialized spectrometer was designed and developed to measure the mass and velocity distributions of neutral particles (molecules and molecular clusters) released from metal-backed Teflon and Kapton films. Promising results were obtained with an insulation breakdown initiation system based on a moveable contact touching the insulated surfaces. A variable energy, high voltage pulse is applied to the contact. The resulting surface damage sites can be made similar in size and shape to those produced by a high voltage electron beam system operating at similar discharge energies. The point discharge apparatus was used for final development of several high speed recording systems and for measurements of the composition of the materials given off by the discharge. Results with this apparatus show evolution of large amounts of fluorocarbon fragments from discharge through Teflon FEP, while discharges through Kapton produce mainly very light hydrocarbon fragments at masses below about 80 a.m.u.

Kendall, B. R. F.↗

NASA NTRS1982

Charging and discharging characteristics of dielectric materials exposed to low- and mid-energy electrons

Charging and discharging characteristics of dielectric samples exposed to 1-25 keV and 25-100 keV electrons in a laboratory environment are reported. The materials examined comprised OSR, Mylar, Kapton, perforated Kapton, and Alphaquartz, serving as models for materials employed on spacecraft in geosynchronous orbit. The tests were performed in a vacuum chamber with electron guns whose beams were rastered over the entire surface of the planar samples. The specimens were examined in low-impedance-grounded, high-impedance-grounded, and isolated configurations. The worst-case and average peak discharge currents were observed to be independent of the incident electron energy, the time-dependent changes in the worst case discharge peak current were independent of the energy, and predischarge surface potentials are negligibly dependent on incident monoenergetic electrons.

Coakley, P.↗

NASA NTRS1983

Dielectric surface discharges - Effects of combined low-energy and high-energy incident electrons

Balmain, K. G.↗

NASA NTRS1984

Adaptive microwave reflector

As an interim step in going to the 100-meter reflector that was evaluated, a 5-meter reflector is proposed to test the electrostatic concept under space conditions. Some of the issues which require the space environment for evaluation are the following questions: Can deployment of a box ring structure with a thin film reflector attached be manually deployed? In the absence of humidity, can a 0.3-mil aluminized Kapton film reflector be formed by the electrostatic process suitable for antenna applications? Can the photogrammetric process be used to evaluate the reflector surface with pictures taken from the payload handling station? Can the space charging effect be evaluated with the 5-meter reflector attached to the Shuttle? Does the outgassing of moisture from 0.3-mil Kapton film affect its reflector capability? A box ring truss support structure and an automatic sequence deployment system are discussed.

Goslee, J. W.↗