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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 NTRS1979

Charging rates of metal-dielectric structures

Metal plates partially covered by 0.01-centimeter-thick fluorinated ethylene-propylene (FEP) Teflon were charged in the Lewis Research Center's geomagnetic substorm simulation facility using 5-, 8-, 10-, and 12-kilovolt electron beams. Surface voltage as a function of time was measured for various initial conditions (Teflon discharged or precharged) with the metal plate grounded or floating. Results indicate that both the charging rates and the levels to which the samples become charged are influenced by the geometry and initial charge state of the insulating surfaces. The experiments are described and the results are presented and discussed. NASA charging analyzer program (NASCAP) models of the experiments have been generated, and the predictions obtained are described. Implications of the study results for spacecraft are discussed.

Purvis, C. K.↗
NASA NTRS1979

Development of a prototype flexible radiator system

The radiator is a roll-up flexible panel with the transport fluid manifolds located at the ends of the 27 foot length. A total of fifty Teflon flow tubes are sandwiched between the layers of silver wire mesh and sealed in the Teflon film. The transport fluid flows from an inlet manifold through 25 panel flow tubes to the end of the radiator panel into a manifold which directs the fluid into the other 25 flow tubes on its return to the base of the radiator. Deployment/retraction of the flexible radiator panel is by low pressure inflation tubes (one along each side of the panel) which incorporate a flat spring. The spring supplies the retraction force to wind the radiator panel on a drum when the pressure in the inflation tubes is relieved. Room ambient deployment tests of the radiator panel were conducted to verify the inflation tube spring deployment, and retraction capability. The panel underwent a thermal vacuum, solar spectrum exposure test. After approximately 100 hours of solar exposure, post-test inspection revealed no structural or optical properties degraded.

Hixon, C. W.↗
NASA NTRS1979

UV blocking filters for polymeric films

The concept of incorporating UV screening agents in silicone resins as a means of protecting underlying solar cell covers and adhesives from UV degradation is presented. A silicone hard-coat resin incorporating a UV screening agent was selected as a suitable coating material for PFA Teflon solar cell covers. Consideration is given to fabrication procedures and techniques for introduction of the UV screening agents into silicone resins and application of these UV-inhibited coatings to the Teflons. Some preliminary environmental tests, such as thermal shock and temperature humidity, were conducted.

Rayl, G. J.↗
NASA NTRS1979

Toughening of thermosetting polyimides

Work directed toward increasing the resistance to crack propagation of thermoset polyimides is described. Rubber modification and Teflon microfiber impregnation techniques for increasing fracture toughness are investigated. Unmodified Kerimid 601 has a fracture surface work value of 0.20 in-lbs/sq in. Dispersed particles of amine terminated butadiene acrylonitrile liquid rubber or of silicone rubber do not raise this value much. By contrast, 5 percent of well fibrillated Teflon produces an eight-fold increase in fracture toughness. Further process improvements should increase this factor to 20-30.

Gollob, D. S.↗
NASA NTRS1979

A small, passively operated hydrogen maser

The paper describes a compact passive hydrogen maser with unique features including a reduction in size. It uses a passive operation mode, permitting the use of a small microwave TE(011) cavity dielectrically loaded by a low loss alumina. The Teflon coated quartz bulb common in other masers has been replaced by a Teflon coating on the inside wall of the cavity producing a simpler designed and a more rugged H-maser package. The cavity and the attached endcaps comprise the vacuum envelope, allowing the use of a single vacuum system. The dimensional stability of the ceramic cavity under barometric changes is sufficiently within the range of the electronic cavity servo so that a second vacuum system is not required. For temperature control, a single oven is located in the magnetic shield nest.

Howe, D. A.↗
NASA NTRS1981

Fatigue degradation in compressively loaded composite laminates

The effect of imbedded delaminations on the compression fatigue behavior of quasi-isotropic, T300/5208, graphite/epoxy laminates was investigated. Teflon imbedments were introduced during panel layup to create delaminations. Static and constant amplitude (R=10, omega = 10 Hz) fatigue tests were conducted. S-N data and half life residual strength data were obtained. During static compression loading, the maximum deflection of the buckled delaminated region was recorded. Under compression fatigue, growth of the imbedded delamination was identified as the predominant failure mode in most of the test cases. Specimens that exhibited others failures had a single low stiffness ply above the Teflon imbedment. Delamination growth during fatigue was monitored using DIB enhanced radiography. In specimens with buried delaminations, the dye penetrant (DIB) was introduced into the delaminated region through a minute laser drilled hole, using a hypodermic needle. A low kV, microfocus, X-ray unit was mounted near the test equipment to efficiently record the cyclic growth of buried delaminations on Polaroid film.

Ramkumar, R. L.↗
NASA NTRS1980

Study of thermal control systems for orbiting power systems. Materials experiment carrier thermal control system study

Four possible arrangements of the materials experiment carrier (MEC) and power system (PS) thermal control loops were defined which would provide one kW of heat rejection for each kW of power to the MEC payload. These arrangements were compared to the baseline reference concept which provides only 16 kW heat rejection to show the cost of obtaining symmetry in terms of dollars, weight, complexity, growth potential, ease of integration, technology and total launch weight. The results of these comparisons was that the concept which splits the PS thermal control loop into two systems, one to reject PS waste heat and one payload waste heat, appeared favorable. The fluid selection study resulted in recommendation of FC72 as the MEC heat transport fluid based on the thermal and physical characteristics. The coatings reviewed indicated anodized and alodine treated aluminum surfaces or silver teflon are the best choices for the MEC vehicle where durability is an important factor. For high temperature radiators silver teflon or zinc orthotitanate are recommended choices.

Fleming, M. L.↗
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 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 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 NTRS1983

Investigation of a pulsed electrothermal thruster

Exhaust velocity and thrust measurements are performed on a pulsed electrothermal thruster using polyethylene and Teflon propellants. The results verify theoretical predictions of equilibrium flow in the nozzle, resulting in substantial recovery of the energy of dissociation and ionization. The thruster is tested in an unsteady mode (15 micro sec current pulse and 15 cm discharge length) and in a quasi-steady mode (48 micro sec current pulse and 5 cm discharge length). All tests are run at 2 kJ. The exhaust velocity of the propellant mass exiting during the current pulse is measured with two types of time of flight probes, and the impulse bit is measured on a thrust stand. It is inferred from both theory and experiment that an additional amount of mass is exhausted after the pulse. The measured thrust to power ratio for polyethylene is T/P = 0.10 NkW at 21 km/sec in the unsteady mode, and T/P = .053 N/kW at 27 km/sec in the quasi-steady mode, where the velocities are measured by the time-of-flight probes. For Teflon propellant, T/P = .20 N/kW at 15 km/sec (unsteady mode) and 0.090 N/kW at 20 km/sec (quasi-steady mode). The discharge pressure and temperature predicted by a computational model for polyethylene are consistent with the measured thrust and discharge resistance.

Burton, R. L.↗
NASA NTRS1985

Nickel-Cadmium Cell Design Variable Program Data Analysis

A program was undertaken in conjunction with the General Electric Company to evaluate 9 of the more important nickel cadmium aerospace cell designs that are currently being used or that have been used in the past 15 years. Design variables tested in this program included teflonated negative plates, silver treated negative plates, light plate loading level, no positive plate cadmium treatment, plate design of 1968 utilizing both old and new processing techniques, and electrochemically impregnated positive plates. The data acquired from these test packs in a low Earth orbit cycling regime is presented and analyzed here. This data showed conclusively that the cells manufactured with no positive plate cadmium treatment outperformed all other cell designs in all aspects of the program and that the cells with teflonated negative electrodes performed very poorly.

Morrow, G. W.↗
NASA NTRS1985

Nickel Cadmium Cell Design Variable Program Data Analysis

A program was undertaken to evaluate eight of the more important nickel-cadmium cell designs that are currently being used or that have been used during the past 15 years. Design variables tested in this program included teflonated negative plates, silver treated negative plates, light plate loading level, no positive plate cadmium treatment, plate design of 1968, utilizing both old and new processing techniques, and electrochemically impregnated positive plates. The data acquired from these test packs in a low Earth orbit cycling regime is presented and analyzed here. This data showed conclusively that the cells manufactured with no positive plate cadmium treatment outperformed all other cell designs in all aspects of the program and that the cells with teflonated negative electrodes performed very poorly.

Morrow, G. W.↗
NASA NTRS1986

Investigation of fiber bridging in double cantilever beam specimens

The possibility to eliminate fiber bridging or at least to reduce it, and to evaluate an alternative approach for determination of in situ mode 7 fracture toughness values of composite matrix materials were investigated. Double cantilever beam (DCB) specimens were made using unidirectional lay-ups of T6C/Hx205 composite material in which the delaminating halves were placed at angles of 0, 1.5, and 3 degrees to each other. The small angles between the delaminating plies were used to avoid fiber nesting without significantly affecting mode I teflon insert. The DCB specimens were fabricated and it was found that: (1) the extent which fiber bridging and interlaminar toughness increase with crack length can be reduced by slight cross ply at the delamination plane to reduce fiber nesting; (2) some fiber bridging may occur even in the absence of fiber nesting; (3) the first values of toughness measured ahead of the thin teflon insert are very close to the toughness of the matrix material with no fiber bridging; (4) thin adhesive bondline of matrix material appears to give toughness values equal to the interlaminar toughness of the composite matrix without fiber bridging.

Johnson, W. S.↗
NASA NTRS1986

A simple antireflection overcoat for opaque coatings in the submillimeter region

An antireflection overcoat for opaque baffle coatings in the far infrared (FIR)/submillimeter region was made from a simple Teflon spray-on lubricant. The Teflon overcoat reduced the specular reflectance of four different opaque coatings by nearly a factor of two. Analysis, based on the interference term of a reflecting-layer model, indicates that in the submillimeter region the reduced reflectance depends primarily on the refractive index of the overcoat and very little on its thickness.

Smith, S. M.↗
NASA NTRS1986

Transmission electron microscopic examination of phosphoric acid fuel cell components

Transmission electron microscopy (TEM) was used to physically characterize tested and untested phosphoric acid fuel cell (PAFC) components. Those examined included carbon-supported platinum catalysts, carbon backing paper, and Teflon-bonded catalyst layers at various stages of fabrication and after testing in pressurized PAFC's. Applicability of electron diffraction and electron energy loss spectroscopy for identifying the various phases was explored. The discussion focuses on the morphology and size distribution of platinum, the morphology and structural aspects of Teflon in catalyst layers, and the structural evidence of carbon corrosion. Reference is made to other physical characterization techniques where appropriate. A qualitative model of the catalyst layer that emerged from the TEM studies is presented.

Pebler, A.↗
NASA NTRS1986

Simple antireflection overcoat for opaque coatings in the submillimeter region

An antireflection overcoat for opaque baffle coatings in the far-IR/submillimeter region has been made from a simple Teflon spray-on lubricant. The Teflon overcoat reduced the specular reflectance of four different opaque coatings by nearly a factor or 2. Analysis, based on the interference term of a reflecting-layer model, indicates that in the submillimeter region the reduced reflectance depends primarily on the refractive index of the overcoat and very little on its thickness.

Smith, S. M.↗
NASA NTRS1986

Geometric radiating surfaces for spacecraft thermal control

Various geometric radiating surface (GRS) configurations are evaluated analytically and experimentally for potential use in spacecraft thermal control systems. Egg-crate, honeycomb, flat-parallel, curved-parallel, chevron-shape, and composite fin radiator panel designs were evaluated in terms of mass, apparent emissivity, meteoroid protection, and ease of fabrication; the parallel-finned GRS in composite form was chosen as the most efficient design. The performance of the composite-finned GRS was compared with that of a silver-backed Teflon radiator. The emissivity and dissipative power capabilities of the GRS and radiator are measured. It is observed that the composite-finned GRS has 34 percent less surface area, 34 percent higher heat flux capability, greater meteoroid protection, and 2.8 times higher mass than the Teflon radiator. Future developments and applications for GRCs are discussed.

Keddy, M. D.↗