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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Multi-spacecraft observations of collisionless shocks

The ability to make simultaneous, multipoint measurements of field and plasma properties has substantially increased knowledge of the structure and physics of collisionless shocks in space. In addition to allowing the determination of the large-scale macroscopic structure of such shocks as well as reliable estimates of shock normal direction, multipoint measurements have made it possible to measure shock thicknesses and speeds under a variety of upstream conditions. This ability has enabled a number of quantitative analyses of shock structure, including the confirmation of the dispersive whistler-mode character at low Mach numbers, the assessment of the relative importance of magnetic and electrostatic forces within the shock, and a detailed examination of possible dissipation mechanisms.

Thomsen, M. F.↗
NASA NTRS1988

Multi-spacecraft observations of magnetopause surface waves - ISEE 1 and 2 determinations of amplitude, wavelength and period

The multispacecraft ISEE mission made it possible to study propagation of surface waves on the magnetopause. One case studied in detail was near local noon at a latitude of 24.4 deg. The inferred instantaneous magnetopause normal vectors oscillated about the model magnetopause normal vector in a manner expected for a wave propagating along the magnetopause from the subsolar region. By assuming a model monochromatic wave and a constant magnetopause thickness, the best-fit that yields the three wave parameters( amplitude, wavelength, and period) is determined.

Song, PU↗
NASA NTRS1989

Development of cost-effective standards for Earth observation spacecraft

A program to accomplish a technical interdisciplinary approach to international standards development is described. Working groups include: remote sensing spacecraft, sensing system, operations, and communication and data systems. Additionally, the software reliability and international liaison working groups are discussed.

Federoff, Andrea M.↗
NASA NTRS1992

Modelling atmospheric scatterers using spacecraft observations

Voyager images of Triton indicate considerable spatial variability in the concentration of at least two different scattering components in the atmosphere. Data from high phase angle limb scans were fit to Mie scattering models to derive mean particle sizes, number densities, and vertical extent for both types of scattering material at ten different locations between 15 deg S and 70 deg S. These fits reveal a thin haze at latitudes equatorward of 25-30 deg S. The imaging data can be fit reasonably well by both conservatively scattering and absorbing hazes with particle sizes near 0.18 micron and optical depths of order 0.001-0.01. Rayleigh scattering haze fits the imaging data somewhat less well, and can be totally ruled out by combining the imaging and UVS measurements. At high southern latitudes, Triton displays clouds below an altitude of approximately 8 km, as well as the haze at higher altitudes. The clouds have particle sizes which may range from 0.7-2.0 microns, or may be near 0.25 micron. The atmospheric optical depth poleward of 30 deg S must be generally greater than 0.1, but need not be more than 0.3. Horizontal inhomogeneities are quite noticeable, especially at longitudes east of (i.e., higher than) 180 deg.

Rages, Kathy A.↗
NASA NTRS1999

Modelling Atmospheric Scattering Using Spacecraft Observations

The period covered by this cooperative agreement included the analysis of data from the Voyager encounter with Neptune and Triton and the primary Galileo mission to Jupiter (including the Galileo Probe entry into Jupiter's atmosphere), as well as continued work on Uranus' seasonal variability using the Voyager encounter data as a baseline.

Rages, Kathy A.↗
NASA NTRS1999

Modelling Atmospheric Scatterers Using Spacecraft Observations

This project report reviews the analysis of data from the Voyager encounter with Neptune and Triton, and the primary Galileo mission to Jupiter. The project included analysis of the images from Voyager of the limb images from Neptune and Triton. Also included in the project was analysis of the Images from Galileo of Venus' and Jupiter's limb. The project work on the latitude bands and temporal variations on Uranus using the images from Voyager is summarized. Also, work on information from the Galileo Probe's Nephelometer is also covered

Rages, Kathy A.↗
NASA NTRS2003

Obliquity, Ice Sheets, and Layered Sediments on Mars: What Spacecraft Observations and Climate Models are Telling Us

The Mars Odyssey Gamma-Ray Spectrometer (GRS) data present a quandary: On the one hand, large deposits of (inferred) water ice are located where thermal models suggest they would form and best be protected, e.g., if deposited during periods of higher obliquity. On the other hand, the volume mixing ratios (approx. 70%) are so high that diffusive deposition of water in regolith pore space (which is the process assumed by these models) cannot be the primary formation mechanism. Furthermore, given that the water is inferred to be so close to the surface (less than a few 10's of cm's), it must be in communication with the atmosphere on time scales that are geologically relatively short (10(exp 3)-10(exp 6) years); therefore the water cannot be archaic. Considering the GRS data, images of mantled, fretted, and disaggregated terrain, and new climate modeling of Mars orbital cycles, we are led to an alternate conclusion about the ice deposits: that they form as subaerial ice sheets. This scenario not only provides a simple explanation for these observations, but may also help explain the formation of globally distributed, sedimentary layered deposits.

Richardson, M. I.↗
NASA NTRS2011

Multi-Spacecraft Observations of Saturn Kilometric Radio Emission

Saturn kilometric radiation (SKR) is the auroral radio emission of Saturn, which has been observed by Voyager 1 & 2, Cassini, and Ulysses. Ulysses is able to detect the intense intervals of SKR from distances up to 10 AU, because of its long antennas (72 m tip-to-tip) and sensitive radio receivers. Studies of SKR by A. Lecacheux gave the surprising result that the periodicity of SKR varied with time; it was not locked to a planetary rotation of Saturn. This result has been confirmed by Cassini radio observations. Here, we compare Ulysses and Cassini observations of SKR to constrain a mode! for the SKR emission geometry. SpecifIcally, we examine the question - are the brighter sources of 5KR fixed in Saturn longitude or local time? The results have significant consequences for our understanding of SKR and its varying periodicity

MacDowall, R. J.↗
NASA NTRS1982

Comparison of Venusian lightning observations

Spacecraft observations of Venusian lightning are reviewed to determine the energy dissipation rate. Optical sensors provide data on the total energy dissipated per flash, so long as the contributions of atomic oxygen and ionized carbon are accounted for. Radio probes yield information on the total lightning occurrences. Venera 9-12 radio surveys are reviewed, and event rates of 20-30/sec for Venera 11 are mentioned. Venera 9 observed a sole, 70 sec event period on the Venusian nightside. Comparisons are made between the recorded electromagnetic energy levels and terrestrial lightning data. The nightside occurrence rate is calculated to be 0.08 strokes/sq km per year, while the dayside exhibits 85 flashes/sq km per sec. Energy dissipation rates ranging from 0.0012-0.25 W/sq m are calculated for various flash durations. It is suggested that the lightning occurs in the clouds as part of an organized meteorological system.

Borucki, W. J.↗
NASA NTRS2003

Using an MHD simulation to interpret the global context of a coronal mass ejection observed by two spacecraft

In late February 1999 the ACE spacecraft observed a coronal mass ejection (CME) at 1 AU, in the ecliptic plane. Thirteen days later, Ulysses observed a CME at 5 AU and 22"s. We present a detailed analysis of the plasma, magnetic field, and composition signatures of these two events. On the basis of this comparison alone, it is not clear that the two spacecraft observed the same solar event. However, using a generic MHD simulation of a fast CME initiated at the Sun by magnetic flux cancellation and propagated out into the solar wind, together with additional evidence, we argue that indeed the same CME was observed by both spacecraft. Although force-free models appear to fit the observed events well, our simulation results suggest that the ejecta underwent significant distortion during its passage through the solar wind, indicating that care should be taken when interpreting the results of force-he models. Comparison of composition measurements at the two spacecraft suggests that significant spatial inhomogeneities can exist within a single CME.

Riley, Pete↗
NASA NTRS1988

In situ acceleration and gradients of charged particles in the outer solar system observed by the Voyager spacecraft

Observations of interplanetary acceleration events from about 1 to about 25 AU are presented. It is shown that shock structures have a profound effect on high energy (greater than or equal to 70 MeV) cosmic rays, especially during solar minimum, when a negative latitudinal gradient was observed after early 1985 at all energies from about 70 MeV down to about 30 keV. The observations suggest that local acceleration to a few hundred MeV, and as high as a few GeV, is continually present throughout the heliosphere.

Krimigis, S. M.↗