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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 1,189 records · Page 66
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Characterization of electrical discharges on Teflon dielectrics used as spacecraft thermal control

The dual effects of system degradation and reduced life of synchronous-orbit satellites as a result of differential spacecraft charging underscore the need for a clearer understanding of the prevailing electrical discharge phenomena. In a laboratory simulation, the electrical discharge current, surface voltage, emitted particle fluxes, and photo-emission associated with discharge events on electron beam irradiated silver-backed Teflon samples were measured. Sample surface damage was examined with optical and electron beam microscopes. The results are suggestive of a model in which the entire sample surface is discharged by lateral sub-surface currents flowing from a charge deposition layer through a localized discharge channel to the back surface of the sample. The associated return current pulse appears to have a duration which may be a signature by which different discharge processes may be characterized.

Yadlowsky, E. J.↗
NASA NTRS1979

Auroral mechanisms and morphology

The present review is concerned with observations, analysis of observations and theoretical work as related to the understanding of the aurora. The ground-based observations reviewed include (1) auroral imagery, both by television and all-sky camera; (2) gross magnetic variations indicative of ionospheric currents; (3) VLF hiss observations; and (4) effects of high-energy electron impact measured through cosmic radio noise absorption and by observations of bremsstrahlung X-ray from balloons. Spectroscopic observations, observation of micropulsation activity and auroral radar observations are not included, since they seem to provide less direct diagnostic information on the basic auroral mechanism. Incoherent scatter radar observations are utilized to the extent they provide information on ionospheric currents and electric fields. Satellite observations are included to the extent they provide information on the aurora or useful clues to auroral mechanisms. Barium injection experiments in the auroral zone are also considered.

Swift, D. W.↗
NASA NTRS1981

Optically induced bistable states in metal/tunnel-oxide/semiconductor /MTOS/ junctions

A new switching phenomenon in metal-oxide semiconductor tunnel junction has been discovered. With a sufficiently large negative bias applied to the electrode, incident visible light of intensity greater than about 1 microW/sq cm causes the reverse-biased junction to switch from a low-current to a high-current state. It is believed that hot-electron-induced impact ionization provides the positive feedback necessary for switching, and causes the junction to remain in its high-current state after the optical excitation is removed. The junction may be switched back to the low-current state electrically. The basic junction characteristics have been measured, and a simple model for the switching phenomenon has been developed.

Lai, S. K.↗
NASA NTRS1981

Parasitic current losses due to solar electric propulsion generated plasmas

Solar electric propulsion is a leading candidate for many upcoming space missions. Under many circumstances plasma produced by charge-exchange reactions within the ion beam dominates the ambient environment near the spacecraft. The calculations presented here contain a predictive hydrodynamic model for the charge-exchange plasma expansion, and a fully three-dimensional model for the structure of the plasma sheath around the solar array wing. Results of calculations for several configurations and voltage levels indicate that with kilovolt biases power losses of approximately 10 percent or more are likely, even with only one engine in operation, and that ameliorative measures should focus on the inboard portion of the solar arrays.

Katz, I.↗
NASA NTRS1982

Computer simulation of inner magnetospheric dynamics for the magnetic storm of July 29, 1977

The Rice University convection model is applied to the early main phase of the July 29, 1977 magnetic storm through a computer implementation that self-consistently calculates electric fields, currents, and plasma distributions and velocities in the inner magnetosphere/ionosphere system. On the basis of solar wind parameters and AL index as inputs, the model predicts the injection of plasma sheet plasma to form a substantial storm time ring current whose total predicted strength agrees with the observed Dst index. The possibility that the magnetic field may be sufficiently inflated to make 60 deg field lines extend to the outer magnetosphere is examined. In the model, distortion of the plasma sheet inner edge by magnetospheric compression associated with the sudden commencement temporarily disrupts the normal Birkeland current pattern. Normal Birkeland currents and shielding reassert themselves in about an hour.

Wolf, R. A.↗
NASA NTRS1983

Solar photovoltaic powered refrigerators/freezers for medical use in remote geographic locations

One of the obstacles preventing widespread immunication against disease is the virtual absence of reliable, low maintenance refrigeration systems for storage of vaccines in remote geographic locations. A system which consists of a solar photovoltaic cell array and an integrated refrigerator/freezer-energy storage unit is discussed herein. The array converts solar radiation into direct current (DC) electricity with no moving parts and no intermediate steps. A detailed description of the refrigeration system, its design and an analysis thereof, performance test procedures, and test results are presented. A system schematic is also provided.

Darkazalli, G.↗
NASA NTRS1984

Models of auroral-zone conductances

The magnetosphere-ionosphere system is strongly coupled, with magnetospheric Birkeland currents feeding ionospheric Pedersen and Hall currents. Central to any computer simulation of this system is a detailed, valid conductivity model. An accurate conductivity model is also vital in order to infer Birkeland currents and electric field patterns from inversions of magnetometer chain data. Several recent attempts at constructing conductivity models are presented and their strengths and weaknesses discussed. Incoherent scatter radar measurements can determine height profiles of electron content, from which Pedersen and Hall conductances may be calculated. These yield excellent spatial and good temporal resolution; however, they are limited in field of view. A global pattern requires either 24 hours of data or a chain of stations. Synoptic empirical models (quantized by indices such as Kp or AE) typically are limited by their large bin size (1 deg invariant latitude x 1 hour MLT), and cannot reproduce arcs. Estimating conductivity globally from Dynamics Explorer auroral images is promising, and can yield reasonable time scales (of about 10 minutes); however, this procedure is still only now being tested.

Reiff, P. H.↗
NASA NTRS1985

Electric field effects on ion currents in satellite wakes

Small currents associated with satellite spin, dielectric conduction, or trace concentrations of H+, can have a substantial effect on the potential of a satellite and the particle currents reaching its surface. The importance of such small currents at altitudes below about 300 km stems from the extremely small 0+ currents impinging on the wake-side of the spacecraft. The particle current on the downstream side of the AE-C satellite is considered. Theoretical estimates based on a newly described constant of the motion of a particle indicate that accounting for small concentrations of H+ remove a major discrepancy between calculated and measured currents.

Parks, D. E.↗
NASA NTRS1985

A new source of suprathermal O(+) ions near the dayside polar cap boundary

A large number of data on suprathermal O(+) ions taken during the retarding ion mass spectrometer (RIMS) experiment aboard the DE 1 satellite are surveyed. Examples are found of low-energy, upflowing O(+) which are consistent with one or more of the proposed ionospheric escape mechanisms. These include transversely accelerated O(+) ions, indicating low-altitude transverse acceleration, and O(+) field-aligned flows which indicate low-altitude parallel acceleration by either ambipolar or current-driven electric fields. However, by far the most common pitch angle distribution of escaping O(+) is found to be a new type of O(+) flow event which provides evidence for both perpendicular and parallel ion acceleration below the satellite and is found exclusively in the lower latitudes of the dayside polar cap. All species of ions are observed to move upward during these events, with an upward heat flux.

Lockwood, M.↗
NASA NTRS1986

Spacecraft mass spectrometer ion source employing field emission cathodes

An ion source that utilizes a pair of thin-film field emission cathodes to provide current for electric impact ionization is studied. The field emission cathodes are composed of microscopically small needle tips and an extraction electrode; the cathodes generate a 200-eV, 0.1-mA electron beam. The multistep process for the manufacturing of the field emission cathodes is examined. The operation of the ion source, which ionizes atoms and molecules that enter the mass spectrometer with a ram velocity of about 80 km/sec, is described.

Curtis, C. C.↗
NASA NTRS1987

Quadrennial review of the magnetotail

The findings of research conducted on the magnetotail in the years 1983-1986 are presented. The topics discussed include observations of the distant (between 60 and 220 earth radii) and the near-earth (earthward of 35 earth radii) magnetotail regions by the ISEE l, 2, and 3 and IMP 8 spacecraft, and magnetotail theory and modeling. These studies established the association between substorms and plasmoids in the deep tail and the linkage between the magnetosphere and the ionosphere via field-aligned currents and electric fields.

Huang, C. Y.↗
NASA NTRS1990

Emerging applications of high temperature superconductors for space communications

Proposed space missions require longevity of communications system components, high input power levels, and high speed digital logic devices. The complexity of these missions calls for a high data bandwidth capacity. Incorporation of high temperature superconducting (HTS) thin films into some of these communications system components may provide a means of meeting these requirements. Space applications of superconducting technology has previously been limited by the requirement of cooling to near liquid helium temperatures. Development of HTS materials with transition temperatures above 77 K along with the natural cooling ability of space suggest that space applications may lead the way in the applications of high temperature superconductivity. In order for HTS materials to be incorporated into microwave and millimeter wave devices, the material properties such as electrical conductivity, current density, surface resistivity and others as a function of temperature and frequency must be well characterized and understood. The millimeter wave conductivity and surface resistivity were well characterized, and at 77 K are better than copper. Basic microwave circuits such as ring resonators were used to determine transmission line losses. Higher Q values than those of gold resonator circuits were observed below the transition temperature. Several key HTS circuits including filters, oscillators, phase shifters and phased array antenna feeds are feasible in the near future. For technology to improve further, good quality, large area films must be reproducibly grown on low dielectric constant, low loss microwave substrates.

Heinen, Vernon O.↗
NASA NTRS1989

Currents between tethered electrodes in a magnetized laboratory plasma

Laboratory experiments on important plasma physics issues of electrodynamic tethers were performed. These included current propagation, formation of wave wings, limits of current collection, nonlinear effects and instabilities, charging phenomena, and characteristics of transmission lines in plasmas. The experiments were conducted in a large afterglow plasma. The current system was established with a small electron-emitting hot cathode tethered to an electron-collecting anode, both movable across the magnetic field and energized by potential difference up to V approx.=100 T(sub e). The total current density in space and time was obtained from complete measurements of the perturbed magnetic field. The fast spacecraft motion was reproduced in the laboratory by moving the tethered electrodes in small increments, applying delayed current pulses, and reconstructing the net field by a linear superposition of locally emitted wavelets. With this technique, the small-amplitude dc current pattern is shown to form whistler wings at each electrode instead of the generally accepted Alfven wings. For the beam electrode, the whistler wing separates from the field-aligned beam which carries no net current. Large amplitude return currents to a stationary anode generate current-driven microinstabilities, parallel electric fields, ion depletions, current disruptions and time-varying electrode charging. At appropriately high potentials and neutral densities, excess neutrals are ionized near the anode. The anode sheath emits high-frequency electron transit-time oscillations at the sheath-plasma resonance. The beam generates Langmuir turbulence, ion sound turbulence, electron heating, space charge fields, and Hall currents. An insulated, perfectly conducting transmission line embedded in the plasma becomes lossy due to excitation of whistler waves and magnetic field diffusion effects. The implications of the laboratory observations on electrodynamic tethers in space are discussed.

Stenzel, R. L.↗
NASA NTRS1993

Computer code for scattering from impedance bodies of revolution. Part 3: Surface impedance with s and phi variation. Analytical and numerical results

The third phase of the development of the computer codes for scattering by coated bodies that has been part of an ongoing effort in the Electromagnetics Laboratory of the Electrical Engineering and Computer Science Department at the University of Illinois at Chicago is described. The work reported discusses the analytical and numerical results for the scattering of an obliquely incident plane wave by impedance bodies of revolution with phi variation of the surface impedance. Integral equation formulation of the problem is considered. All three types of integral equations, electric field, magnetic field, and combined field, are considered. These equations are solved numerically via the method of moments with parametric elements. Both TE and TM polarization of the incident plane wave are considered. The surface impedance is allowed to vary along both the profile of the scatterer and in the phi direction. Computer code developed for this purpose determines the electric surface current as well as the bistatic radar cross section. The results obtained with this code were validated by comparing the results with available results for specific scatterers such as the perfectly conducting sphere. Results for the cone-sphere and cone-cylinder-sphere for the case of an axially incident plane were validated by comparing the results with the results with those obtained in the first phase of this project. Results for body of revolution scatterers with an abrupt change in the surface impedance along both the profile of the scatterer and the phi direction are presented.

Uslenghi, Piergiorgio L. E.↗
NASA NTRS1995

An inflight refill unit for replenishing research animal drinking water

This paper presents the design process and development approach for a method of maintaining sufficient quantities of water for research animals during a Shuttle mission of long duration. An inflight refill unit (IRU) consisting of two major subsystems, a fluid pumping unit (FPU) and a collapsible water reservoir (CWR), were developed. The FPU provides the system measurement and controls, pump, water lines, and plumbing necessary to collect water coming into the unit from the potable water system and pump it out into the RAHF drinking water tanks. The CWR is a Kevlar (TM) reinforced storage bladder connected to the FPU, which has a capacity of 6 liters in its expanded volume and functions to store the water collected from the potable water system, allowing for transport of the water back to the Spacelab where it is pumped into each of two research animal holding facilities. Additional components of the IRU system include the inlet and outlet fluid hoses, a power cable for providing 29V direct current spacecraft electrical power to the pump within the FPU, a tether system for the unit when in use in Spacelab, and an adapter for mating the unit to the orbiter waste collection system in order to dump excess water after use in Spacelab.

Savage, P. D.↗
NASA NTRS1994

Development of an In-Flight Refill Unit for Replenishing Research Animal Drinking Water

The Spacelab Life Sciences 2 (SLS-2) mission became NASA's longest duration Shuttle mission, lasting fourteen days, when Columbia landed on 1 Nov. 1993. Located within the Spacelab were a total of 48 laboratory rats which were housed in two Research Animal Holding Facilities (RAHF's) developed by the Space Life Sciences Payloads Office (SLSPO) at Ames Research Center. In order to properly maintain the health and well-being of these important research animals, sufficient quantities of food and water had to be available for the duration of the mission. An inflight Refill Unit was developed by the SLSPO to replenish the animals' drinking water inflight using the Shuttle potable water system in the middeck galley as the source of additional water. The Inflight Refill Unit consists of two major subsystems, a Fluid Pumping Unit (FPU) and a Collapsible Water Reservoir (CWR). The FPU provides the system measurement and controls, pump, water lines, and plumbing necessary to collect water coming into the unit from the potable water system and pump it out and into the RAHF drinking water tanks. The CWR is a Kevlar(trademark) reinforced storage bladder, connected to the FPU, which has a capacity of 6 liters in its expanded volume and functions to store the water collected from the potable water system and allows for the transport of the water back to the Spacelab where it is pumped into each of two RAHFs. Additional components of the FPU system include the inlet and outlet fluid hoses, a power cable for providing 28 volt direct current spacecraft electrical power to the pump within the FPU, a tether system for the unit when in use in Spacelab, and an adapter for mating the unit to the orbiter waste collection system in order to dump excess water after use in Spacelab. This paper will present the design process and development approach for the lnflight Refill Unit, define some of the key design issues which had to be addressed, and summarize the inflight operational performance of the unit during the SLS-2 mission.

Savage, P. D.↗
NASA NTRS1999

The Guara Campaign: Rocket-Radar Investigations of the Earth's Upper Atmosphere at the Magnetic and Geographic Equators

The Guara Campaign consisted of a series of sounding rockets that were launched from August to October, 1994 at a new launch facility at Alcantara, Brazil, which is within one degree of the Earth's magnetic equator. The campaign was based on focused scientific experiments designed to investigate the electrodynamics and irregularities in the ionosphere and mesosphere at the Earth's magnetic equator and to study their relationship with neutral upper atmosphere motions. In all, 13 large sounding rockets and 20 small meteorological rockets were launched as part of four different experiment groups designed to investigate: (1) the daytime equatorial electrojet, (2) very high altitude Spread-F processes, (3) sunset electrodynamics, and (4) middle atmosphere-thermosphere coupling at the equator. The instrumentation on the sounding rockets varied with each investigation, but primarily included experiments to measure electric fields, currents, plasma densities,- neutral winds, neutral densities and temperatures, and ionospheric instabilities. All of the experiments utilized ground-based scientific instruments including a VHF backscatter radar interferometer, magnetometers, ionosondes, and scintillation receivers. An overview of each investigation is provided, along with a description of the launch site and the ground-based experiments. Scientific highlights of the campaign are provided.

Pfaff, Robert F., Jr.↗
NASA NTRS2000

Thermal Considerations of Space Solar Power Concepts with 3.5 GW RF Output

This paper presents the thermal challenge of the Space Solar Power (SSP) design concepts with a 3.5 GW radio-frequency (RF) output. High efficiency klystrons are thermally more favored than solid state (butterstick) to convert direct current (DC) electricity to radio-frequency (RF) energy at the transmitters in these concepts. Using klystrons, the heat dissipation is 0.72 GW. Using solid state, the heat dissipation is 2.33 GW. The heat dissipation of the klystrons is 85% at 500C, 10% at 300C, and 5% at 125C. All the heat dissipation of the solid state is at 100C. Using klystrons, the radiator area is 74,500 square m Using solid state, the radiator area is 2,362,200 square m Space constructable heat pipe radiators are assumed in the thermal analysis. Also, to make the SSP concepts feasible, the mass of the heat transport system must be minimized. The heat transport distance from the transmitters to the radiators must be minimized. It can be accomplished by dividing the radiator into a cluster of small radiators, so that the heat transport distances between the klystrons and radiators can be minimized. The area of each small radiator is on the order of 1 square m. Two concepts for accommodating a cluster of small radiators are presented. If the distance between the transmitters and radiators is 1.5 m or less, constant conductance heat pipes (CCHPs) are acceptable for heat transport. If the distance exceeds 1.5 m, loop heat pipes (LHPs) are needed.

Choi, Michael K.↗