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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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NASA NTRS2021

Pyrolysis Rate and Yield Strength Reduction Incarbon Fiber and Glass Fiber Composites Underreentry Heating Conditions

The behavior of composite materials, specifically carbon fiber reinforced plastic (CFRP) and glass fiber reinforced plastic (GFRP), under reentry conditions poses a problem for space debris reentry risk modeling. Since these materials pyrolyze rather than melt and their different components demise at different rates, modeling their destruction to determine ground impact risk is complex. Modern spacecraft are using these materials in ever-greater quantities owing to their superior strength-to-weight characteristics, and this has required that the orbital debris community improve its understanding of how these materials demise on reentry. The NASA Orbital Debris Program Office undertook an extensive test campaign to better understand the rate at which several types of GFRP and CFRP materials pyrolyze under reentry heating conditions and how that pyrolysis affects the ultimate strength of the material. GFRP with a polyester resin (G10/FR-4) and CFRP with epoxy, cyanate ester, vinyl ester, and phenolic resins were tested. The test campaign was carried out at the Inductively Coupled Plasma (ICP) Torch Facility at the University of Texas at Austin. Because the ICP facility operates in a shirt-sleeve environment, test samples can be changed within seconds or minutes, allowing many samples to be tested in a short period. Two heat flux rates, 20 W/m2 and 30W/m2, and two oxygen concentration conditions, 0% and 2% of atmospheric, were applied to all five types of material. To measure both the char rate and the effect of pyrolysis on the ultimate material strength, two types of test were carried out for each material: a char rate test on a ~10 mm thick sample of material and an in-situ bending stress test of a ~2 mm thick sample of material. Measurements of the char rate showed very similar average pyrolysis front velocity in epoxy resin CFRP as in G10 at 3.6 mm/min and 3.4 mm/min, respectively. However, the total mass loss rate in theG10 was nearly double that of the CFRP at 3.8 g/min and 2.2 g/min, respectively. This result represented a slow ablation rate of carbon fibers in the CFRP at the temperatures encountered in low Earth orbit reentry and a comparatively rapid removal of the glass fibers in G10 due to melting and spallation. Pyrolysis front velocity was more significantly affected by the type of plastic than the type of fiber, with the cyanate ester CFRP samples displaying an average pyrolysis front velocity of only 1.9 mm/min. Similarly, the effect of thermal exposure on the ultimate strength of the material depended heavily on the type of plastic and very little on the type of fiber in the material. Epoxy, vinyl ester, and polyester resins all behaved very similarly, with complete structural failure at between 400 J/g and 600 J/g of specific absorbed heat. Phenolic and cyanate ester resins, on the other hand, displayed a change in structural properties that was only barely measurable with the current apparatus even after the maximum exposure time tested. These data are being incorporated into a numerical model of the ablation and demise of composite materials that will be used to more accurately calculate the ground casualty risk of future spacecraft.

Benton R. Greene↗
NASA NTRS1979

A reexamination of plasma measurements from the Mariner 5 Venus encounter

Mariner 5 plasma data from the Venus encounter have been analyzed with twice the time resolution of the original analysis of Bridge et al. (1967). The velocity distribution function for each spectrum is used to determine more precisely the locations of boundaries and characteristic flow parameters in the interaction region around the planet. A new region is identified in the flow located between magnetosheathlike plasma inside the shock front and an interior low-flux region near the geometrical shadow of the planet. The region is characterized by a wide velocity distribution function and a decrease in ion flux. Using the highest time resolution magnetic field data, it is proposed that rapid magnetic field fluctuations in this region may result in an artificial broadening of the distribution function. It is concluded that very high time resolution is required in future experiments in order to determine the true nature of the plasma in this region.

Shefer, R. E.↗
NASA NTRS1972

Magnetospheric plasma.

This paper reviews the principal features of the distribution of plasma in the magnetosphere as inferred from observations of particles with energies in the keV range and below. Low energy electrons are found within the equatorial region of the magnetotail, where they form the plasma sheet, and throughout the outer magnetosphere, where they envelop the earth with a complicated and as yet only partly explored structure. The sum of particle and magnetic pressures is roughly constant across the plasma sheet. The intense electron fluxes of the plasma sheet terminate at the so-called inner boundary of the plasma sheet, which is located at about 11 earth radii in the evening side of the magnetosphere and approaches the plasmapause near the midnight meridian. During substorms, the inner boundary moves closer to the earth, while deep in the magnetotail the plasma sheet first becomes thinner and then expands. Comparison between magnetotail electron densities and whistler measurements suggests that the observed plasma sheet particles may constitute the thermal particle population of the magnetotail.

Vasyliunas, V. M.↗
NASA NTRS1976

Continuum radiation associated with low-energy electrons in the outer radiation zone

A weak nonthermal continuum radiation is generated by the earth's magnetosphere in the frequency range from about 500 Hz to greater than 100 kHz. During magnetically disturbed periods the intensity of this continuum radiation increases significantly. The paper presents a series of observations obtained during a period of greatly enhanced continuum radiation intensity. The enhanced continuum radiation intensities observed during this event are found to be closely correlated with the injection of very intense fluxes of energetic (about 1-30 keV) electrons into the outer radiation zone. Direction-finding measurements of the continuum radiation observed during this event show that the radiation is primarily coming from the dawn side of the magnetosphere, in agreement with the observed dawn-dusk asymmetry in the 1- to 30-keV electron distribution. These results suggest that the continuum radiation may be generated by a coherent plasma instability involving relatively low-energy (about 1-30 keV) electrons rather than by gyrosynchrotron radiation from very energetic (200 keV-1 Mev) electrons as has been previously suggested.

Gurnett, D. A.↗
NASA NTRS1987

Thermal ion complexities observed within the Spacelab 2 bay

Examples of prominent thermal ion composition variations characteristic of the Shuttle environment as observed from within the open cargo bay on the Spacelab 2 mission are discussed. Although the prominent ionization source is the inflow of the ambient plasma, water ions of Shuttle origin were present throughout the mission, and there was evidence for a local source of molecular ions NO(+) and/or O(2+) which also exist in the ionosphere. Bursts in the fluxes of these contaminant species were frequently observed coincident with thruster firings, while O(+) depletions or enhancements could occur depending on the scattering geometry. These effects bring into question whether reliable ambient thermal ion measurements can be made from the vicinity of such vehicles. The presence of significant inflows of contaminant ions into the bay within the Shuttle wake also indicates that Shuttle emissions play a significant role in the evolution of its wake structure.

Grebowsky, J. M.↗
NASA NTRS1993

Low Earth orbital atomic oxygen environmental simulation facility for space materials evaluation

Simulation of low Earth orbit atomic oxygen for accelerated exposure in ground-based facilities is necessary for the durability evaluation of space power system component materials for Space Station Freedom (SSF) and future missions. A facility developed at the National Aeronautics and Space Administrations's (NASA) Lewis Research Center provides accelerated rates of exposure to a directed or scattered oxygen beam, vacuum ultraviolet (VUV) radiation, and offers in-situ optical characterization. The facility utilizes an electron-cyclotron resonance (ECR) plasma source to generate a low energy oxygen beam. Total hemispherical spectral reflectance of samples can be measured in situ over the wavelength range of 250 to 2500 nm. Deuterium lamps provide VUV radiation intensity levels in the 115 to 200 nm range of three to five equivalent suns. Retarding potential analyses show distributed ion energies below 30 electron volts (eV) for the operating conditions most suited for high flux, low energy testing. Peak ion energies are below the sputter threshold energy (approximately 30 eV) of the protective coatings on polymers that are evaluated in the facility, thus allowing long duration exposure without sputter erosion. Neutral species are expected to be at thermal energies of approximately .04 eV to .1 eV. The maximum effective flux level based on polyimide Kapton mass loss is 4.4 x 10 exp 6 atoms/((sq. cm)*s), thus providing a highly accelerated testing capability.

Stidham, Curtis R.↗
NASA NTRS2019

Initial Results from the GEM Challenge on the Spacecraft Surface Charging Environment

Spacecraft surface charging during geomagnetically disturbed times is one of the most important causes of satellite anomalies. Predicting the surface charging environment is one prevalent task of the geospace environment models. Therefore, the Geospace Environment Modeling (GEM) Focus Group "Inner Magnetosphere Crossenergy/Population Interactions" initiated a communitywide challenge study to assess the capability of several inner magnetosphere ring current models in determining surface charging environment for the Van Allen Probes orbits during the 17 March 2013 storm event. The integrated electron flux between 10 and 50 keV is used as the metrics. Various skill scores are applied to quantitatively measure the modeling performance against observations. Results indicate that no model consistently perform the best in all of the skill scores or for both satellites. We find that from these simulations the ring current model with observational flux boundary condition and Weimer electric potential driver generally reproduces the most realistic flux level around the spacecraft. A simple and weaker VollandStern electric field is not capable of effectively transporting the same plasma at the boundary toward the Earth. On the other hand, if the ring current model solves the electric field selfconsistently and obtains similar strength and pattern in the equatorial plane as the Weimer model, the boundary condition plays another crucial role in determining the electron flux level in the inner region. When the boundary flux spectra based on magnetohydrodynamics (MHD) model/empirical model deviate from the shape or magnitude of the observed distribution function, the simulation produces poor skill scores along Van Allen Probes orbits.

Yu, Yiqun↗
NASA NTRS2024

Additively Manufactured Plastic Plasma Spectrometer

We report results in development and testing of a low resource top hat electrostatic analyzer (ESA) for space plasma measurements. This device has been additively manufactured (3D-printed) using fused deposition modeling. The classic top hat design is composed of four plastic pieces, without any surface coatings. The three conducting electrodes are printed from carbon nanotube infused polyether ether ketone (CNT-PEEK). The fourth piece, an insulating electrode support, uses pure PEEK. This ESA is designed to detect electrons in space from 10eV up to 30 keV. We demonstrate that the printed CNT-PEEK is sufficiently electrically conductive to support the fast high voltage slewing often required for high time resolution measurements. The plastic ESA has been successfully vibrated beyond standard pre-flight levels, tested under keV electron beam illumination over a wide range of temperatures, and tested under UV illumination, simulating the solar Ly-α flux. In comparison with an identical machined aluminum ESA, our CNT-PEEK ESA provides nominal energy/angle band passes, closely matching simulation. These band passes imply minimal impact from surface charging at beam energies of 2-3 keV, although more investigation is needed. We also find that the CNT-PEEK ESA provides far superior out-of-band electron rejection and UV photon rejection compared to the machined aluminum ESA. We do not detect any problems with trapped gases or outgassing. This development offers potential for significant mass savings, implementation of otherwise unattainable geometric configurations, and dramatic simplification in manufacturing and assembly processes required for development of space plasma instruments.

Quetzal Larrick↗
NASA NTRS1995

ROSAT PSPC and HRI observations of the composite starburst/Seyfert 2 galaxy NGC 1672

The nearby barred spiral galaxy NGC 1672 has been observed with the Position Sensitive Proportional Counter (PSPC) and High Resolution Imager (HRI) instruments on board the ROSAT X-ray satellite. NGC 1672 is thought to have an obscured Seyfert nucleus, and it has strong starburst activity as well. Three bright X-ray sources with luminosities 1-2 x 10(exp 40) erg/s are clearly identified with NGC 1672. The strongest lies at the nucleus, and the other two lie at the ends of NGC 1672's prominent bar, locations that are also bright in H alpha and near-infrared images. The nuclear source is resolved by the HRI on about the scale of the recently identified nuclear ring, and one of the sources at the ends of the bar is also probably resolved. The X-ray spectrum of the nuclear source is quite soft, having a Raymond-Smith plasma temperature of approximately equals 0.7 keV and little evidence for intrinsic absorption. The ROSAT band X-ray flux of the nuclear source appears to be dominated not by X-ray binary emission but rather by diffuse gas emission. The absorption and emission properties of the sources, as well as their spatial extents, lead us to models of superbubbles driven by supernovae. However, the large density and emission measure of the nuclear X-ray source stretch the limits that can be comfortably accommodated by these models. We do not detect direct emission from the putative Seyfert nucleus, although an alternative model for the nuclear source is thermal emission from gas that is photoionized by a hidden Seyfert nucleus. The spectra of the other two X-ray sources are harder than that of the nuclear source, and have similar difficulties with regard to superbubble models.

Brandt, W. N.↗
NASA NTRS2022

The Contribution of Planetary Period Oscillations Toward Circulation and Mass Loss in Saturn's Magnetosphere

Magnetic reconnection is a process during which magnetic energy is released as kinetic energy. It is considered a crucial driver of energy transport and mass loss within Saturn's magnetosphere. On longterm timescales, is thought to be predominantly driven by the rapid rotation of equatorially mass-loaded flux tubes (i.e., the Vasyliunas cycle), but there is some non-negligible driving from the solar wind as well (i.e., the Dungey cycle). In this study, we investigate an atmospheric driven phenomenon that modulates Saturn's magnetosphere every ∼10.6–10.8 hr, known as planetary period oscillations (PPOs), as an additional driver of magnetic reconnection at Saturn. Using an empirical model of PPO dynamics and Cassini magnetic field and plasma measurements, we find that PPO-driven magnetic reconnection is likely to occur in Saturn's magnetosphere, however, the occurrence of the phenomenon depends on temporally variable characteristics of the PPO systems and spatial asymmetries within Saturn's equatorial magnetosphere. Thus, it is not expected to be an on-going process. On year-long timescales, we find that PPOs are expected to be on par with the Dungey Cycle in driving circulation within Saturn's magnetosphere. However, on ∼1–2 weeks-long timescales, under specific conditions where PPO-driven reconnection is expected to be active, this phenomenon can become more significant than the Vasyliunas cycle, and thus dominate circulation within Saturn's magnetosphere. On year-long timescales, this process is estimated to remove upwards of ∼20% of the mass loaded into the magnetosphere by Enceladus.

O. Agiwal↗
NASA NTRS1978

The interplanetary modulation and transport of Jovian electrons

Based on simultaneous measurements by Pioneer 11 of the 3-6 MeV Jovian electron flux, interplanetary magnetic field magnitude, and solar wind speed, the interplanetary transport of energetic particles is studied. It is found that corotating interaction regions (CIR's) greatly inhibit electron transport across the average field direction. Cross-field transport is also influenced by the degree of compression of the solar wind since CIR's are areas of compressed solar wind plasma. The propagation of Jovian electrons is studied by a model that includes the effects of CIR's. The model tests whether or not the three-dimensional convection-diffusion theory adequately describes the cross-field transport of electrons. The model is also valid for Jovian electron observations from earth-orbiting satellites. The model may be further applied to 1 AU from the sun where it is found that the cross-field diffusion of electrons explains why Jovian electrons are detected at the earth even during periods when the interplanetary magnetic field does not connect the earth directly to Jupiter.

Conlon, T. F.↗
NASA NTRS1986

Evidence of high densities and ion outflows in the polar cap during the recovery phase

The composition and characteristics of the polar cap plasma for an Oct. 14, 1981 outflow of polar wind ions are examined using data from the DE 1 satellite. The on-board instruments included a plasma wave instrument, a retarding ion mass spectrometer (RIMS) and a high altitude plasma instrument (HAPI). The outflow took place at an altitude of about 19,000 km at a magnetic local time of about midnight. The total plasma density measured was about 50/cu cm, which was an order of magnitude higher than normally recorded at that location and altitude. The background hydrogen plasma was disturbed by highly collimated flows of hydrogen and oxygen ions. The H(+) ions had a mean energy of 0.15 eV and a density of 6-10/cu cm. The O(+) ions had an average density of 20/cu cm and a temperature of 0.26 eV. The total flux of outflowing H(+) and O(+) was about 10 million/sq cm per sec. The HAPI data indicated that the O(+) ions appeared in the dayside ionosphere and the H(+) ions detected by the RIMS originated in the nightside polar cap.

Gallagher, D. L.↗
NASA NTRS2011

The Effect on the Lunar Exosphere of a Coroual Mass Ejection Passage

Solar wind bombardment onto exposed surfaces in the solar system produces an energetic component to the exospheres about those bodies. The solar wind energy and composition are highly dependent on the origin of the plasma. Using the measured composition of the slow wind, fast wind, solar energetic particle (SEP) population, and coronal mass ejection (CME), broken down into their various components, we have estimated the total sputter yield for each type of solar wind. We show that the heavy ion component, especially the He++ and 0+7 can greatly enhance the total sputter yield during times when the heavy ion population is enhanced. Folding in the flux, we compute the source rate for several species during different types of solar wind. Finally, we use a Monte Carlo model developed to simulate the time-dependent evolution of the lunar exosphere to study the sputtering component of the exosphere under the influence of a CME passage. We simulate the background exosphere of Na, K, Ca, and Mg. Simulations indicate that sputtering increases the mass of those constituents in the exosphere a few to a few tens times the background values. The escalation of atmospheric density occurs within an hour of onset The decrease in atmospheric density after the CME passage is also rapid, although takes longer than the increase, Sputtered neutral particles have a high probability of escaping the moon,by both Jeans escape and photo ionization. Density and spatial distribution of the exosphere can be tested with the LADEE mission.

Killen, R. M.↗
NASA NTRS1977

Solar wind plasma injection at the dayside magnetospheric cusp

Two mechanisms have been proposed for solar wind particle injection at the dayside magnetospheric cusps: magnetic merging and cross-field diffusion. These two mechanisms are experimentally distinguishable in that they produce different latitudinal distributions of particles penetrating to the low-altitude cusp. An examination of proton and electron measurements obtained by the AE-C satellite in the low-altitude dayside cusp reveals evidence of both types of injection processes. A majority of the injection events, especially the more intense fluxes, are best explained by a merging injection model in which cusp particles are confined to the poleward side of the last closed field line and have a characteristic energy that decreases with increasing latitudinal distance from the last closed field line. Less frequent and less intense injection events are better explained in terms of a diffusive injection of cusp particles onto closed dayside field lines with a characteristic energy that increases with increasing latitudinal distance from the last closed field line. Although diffusion appears to be quantitatively less important than merging in terms of the instantaneous particle injection rate, cross-field diffusion nevertheless appears to proceed at an unexpectedly fast rate, possibly exceeding the Bohm diffusion limit.

Reiff, P. H.↗
NASA NTRS1981

Upper limits for X-ray and energetic neutral particle emission from Jupiter - Voyager-1 results

The X-ray sensitivity of the low energy proton channels in the Low Energy Charged Particle (LECP) experiment and its directional measurements determined whether X-rays from Jupiter can be recognized as additional flux above background as Voyager 1 approached the planet. Between about 230 and about 100 R(J), a statistically significant count rate was detected interpreted as X-rays and/or neutral particles. Such an X-ray flux leads to estimates of precipitating electrons over the Jovian polar caps which are 200 times larger than over observed electron fluxes in the Io plasma torus.

Kirsch, E.↗
NASA NTRS1981

ISEE 1 observations of thermal plasma in the vicinity of the plasmasphere during periods of quieting magnetic activity

An investigation of thermal plasma behavior in the vicinity of the plasmasphere during periods of quieting magnetic activity was conducted by combining thermal ion observations made with the plasma composition experiment on ISEE 1 with plasma density profiles obtained from plasma frequency measurements made with the same satellite's plasma wave experiment. During periods in which the magnetic activity quiets, the two regions characterized by H(+):He(+):O(+) (isotropic) and H(+):O(+):He(+) (field-aligned) ion species distributions (in order of dominance) are separated by a new region in which low-energy H(+) and He(+) are found flowing along the magnetic field lines. At other times, following quieting magnetic activity, distributions having peak fluxes at 90 deg pitch angle are observed in this region.

Horwitz, J. L.↗
NASA NTRS2003

The Plasmoid Thruster Experiment (PTX)

A plasmoid is a compact plasma structure with an integral magnetic field. They have been studied extensively in controlled fusion research and are categorized according to the relative strength of the poloidal and toroidal magnetic field (B(phi), and B(tau), respectively). An object with B(phi)/B(tau) >> 1 is classified as a Field Reverse Configuration (FRC); if B(phi) = B(tau), it is called a Spheromak. There are a number of possible advantages to using accelerated plasmoids for in-space propulsion. A thruster based on this concept would operate by repetitively producing plasmoids and ejecting them from the device at high velocity. The plasmoid is formed inside of a single turn conical theta-pinch coil; as this process is inductive, there are no life-limiting electrodes. Similar experiments have yielded plasmoid velocities of at least 50 km/s (l), and calculations indicate that velocities in excess of 100 km/s are possible. A thruster based on this concept would be capable of producing an I(sp) in the range of 5,000 - 10,OOO s, with thrust densities of order 10(exp 5) N/m(exp 2). The current experiment is designed to produce jet powers in the range of 5-10 kW, although the concept should be scalable to higher power. The purpose of this experiment is to determine the feasibility of this plasma propulsion concept. To accomplish this, it will be necessary to determine: a.) specific impulse and thrust, b.) efficiency and mass utilization, c.) which type of plasmoid (FRC-like or Spheromak-like) gives the best performance, and d.) the characteristics required of actual thruster components (i.e., switch and capacitor technology). The plasmoid mass and velocity will be measured with a variety of diagnostics, including internal and external B-dot probes, flux loops, Langmuir probes, high-speed cameras, and an interferometer. Simulations of the plasmoid thruster using MOQUI, a time dependent MHD code, will be carried out concurrently with experimental testing. The PTX device is currently undergoing initial testing and preliminary experimental results are presented.

Eskridge, Richard↗