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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Proton aurora on Io

The Jovian satellite Io should exhibit substantial auroral activity due to interactions of the satellite's atmosphere with Jovian magnetospheric particles. Plasma sheaths that may form around the satellite will cause substantial proton aurora on the Jupiter-facing hemisphere and electron aurora on the outward-facing hemisphere. A sample calculation indicates that Doppler-shifted radiation from high-velocity hydrogen atoms (proton aurora) will be observable from a spacecraft in the vicinity of Jupiter. Emission near Lyman-alpha may be present at a level as much as 100 times that of the solar background reflected from Io's surface.

Pilcher, C. B.↗
NASA NTRS1977

Multispectral remote observations of hydrologic features on the North Slope of Alaska

Visible and near-infrared Landsat satellite imagery and active and passive aircraft microwave data are used to analyze some hydrologic features in Arctic Alaska. Lake studies using passive microwave imagery reveal that an increase in the microwave brightness temperature correlates with an increase in ice thickness. Synthetic Aperture Radar (SAR) imagery allows determination of lakes that are frozen to the bottom under certain conditions. Landsat imagery of lakes can be used to study summer ice cover dissipation, an indicator of lake depth. River channel morphometry and morphology studies are accomplished using SAR data with good (25 m) resolution. Landsat imagery is shown to be useful for analyzing interannual variations in the extent of river icings (aufeis). Snow depth variations are shown to be potentially discernable using passive microwave data. Finally, the present and potential applications of these remote sensing studies are discussed; these data are useful for locating potable water sources, planning construction in good locations, and for analyzing interannual climate fluctuations.

Hall, D. K.↗
NASA NTRS1980

Upper atmosphere modifications due to chronic discharges of water vapor from space launch vehicle exhausts

The influences of transport, photodissociation, and frequency of injection on the global redistribution of water deposited in the earth's upper atmosphere by repeated launches of large rockets are investigated. Measurable environmental effects of the injected water are found to occur when the mesospheric water vapor mixing ratio exceeds 100 ppmv, which occurs over areas of order 20,000 sq km in connection with possible future Satellite Power System activities. These effects include (1) a 50% reduction in D-region ionization due to screening of L alpha radiation by water; (2) a 50% reduction of D-region ionization as a result of converting NO(+) to water cluster ions which possess more rapid recombination rates; (3) a doubling of OH concentrations below 100 km; and (4) a global doubling of nighttime E-region ionization due to L alpha and L beta radiations geocoronally scattered by atomic hydrogen released by photolysis of H2O. Mixing ratios of 1,000 ppmv necessary for the maintenance of clouds at the mesopause are reached only over areas of order 200 sq km.

Forbes, J. M.↗
NASA NTRS1982

Global thunderstorm activity research survey

The published literature on the subject of the monitoring of global thunderstorm activity by instrumented satellites was reviewed. A survey of the properties of selected physical parameters of the thunderstorm is presented. The concepts used by satellites to identify and to measure terrestrial lightning pulses are described. The experimental data acquired by satellites are discussed. The scientific achievements of the satellites are evaluated against the needs of scientists and the potential requirements of user agencies. The performances of the satellites are rated according to their scientific and operational achievements.

Coroniti, S. C.↗
NASA NTRS1983

Optimizing a remote sensing instrument to measure atmospheric surface pressure

Atmospheric surface pressure can be remotely sensed from a satellite by an active instrument which measures return echoes from the ocean at frequencies near the 60 GHz oxygen absorption band. The instrument is optimized by selecting its frequencies of operation, transmitter powers and antenna size through a new procedure baesd on numerical simulation which maximizes the retrieval accuracy. The predicted standard deviation error in the retrieved surface pressure is 1 mb. In addition the measurements can be used to retrieve water vapor, cloud liquid water and sea state, which is related to wind speed.

Peckham, G. E.↗
NASA NTRS1984

Space Shuttle development update

The development efforts, since the STS-4 flight, in the Space Shuttle (SS) program are presented. The SS improvements introduced in the last two years include lower-weight loads, communication through the Tracking and Data Relay Satellite, expanded extravehicular activity capability, a maneuvering backpack and the manipulator foot restraint, the improvements in thermal projection system, the 'optional terminal area management targeting' guidance software, a rendezvous system with radar and star tracker sensors, and improved on-orbit living conditions. The flight demonstrations include advanced launch techniques (e.g., night launch and direct insertion to orbit); the on-orbit demonstrations; and added entry and launching capabilities. The entry aerodynamic analysis and entry flight control fine tuning are described. Reusability, improved ascent performance, intact abort and landing flexibility, rollout control, and 'smart speedbrakes' are among the many improvements planned for the future.

Brand, V.↗
NASA NTRS1985

Satellite operations support expert system

The Satellite Operations Support Expert System is an effort to identify aspects of satellite ground support activity which could profitably be automated with artificial intelligence (AI) and to develop a feasibility demonstration for the automation of one such area. The hydrazine propulsion subsystems (HPS) of the International Sun Earth Explorer (ISEE) and the International Ultraviolet Explorer (IUS) were used as applications domains. A demonstration fault handling system was built. The system was written in Franz Lisp and is currently hosted on a VAX 11/750-11/780 family machine. The system allows the user to select which HPS (either from ISEE or IUE) is used. Then the user chooses the fault desired for the run. The demonstration system generates telemetry corresponding to the particular fault. The completely separate fault handling module then uses this telemetry to determine what and where the fault is and how to work around it. Graphics are used to depict the structure of the HPS, and the telemetry values displayed on the screen are continually updated. The capabilities of this system and its development cycle are described.

Source record↗
NASA NTRS1986

Instrument characterization for the detection of long-term changes in stratospheric ozone - An analysis of the SBUV/2 radiometer

The scientific objective of unambiguously detecting subtle global trends in upper stratospheric ozone requires that one maintains a thorough understanding of the satellite-based remote sensors intended for this task. The instrument now in use for long term ozone monitoring is the SBUV/2 being flown on NOAA operational satellites. A critical activity in the data interpretation involves separating small changes in measurement sensitivity from true atmospheric variability. By defining the specific issues that must be addressed and presenting results derived early in the mission of the first SBUV/2 flight model, this work serves as a guide to the instrument investigations that are essential in the attempt to detect long-term changes in the ozone layer.

Frederick, J. E.↗
NASA NTRS1987

Energetic magnetospheric ions at the dayside magnetopause - Leakage or merging?

The leakage model for the escape of energetic magnetospheric particles into the magnetosheath is described, making comparisons with the merging model where possible. Reported observations of energetic particles at the dayside magnetopause are reexamined, and it is concluded that they do not conclusively support the merging model, either on a case-by-case basis or statistically. New observations made by the Charge Composition Explorer satellite during the Active Magnetospheric Particle Tracer Explorers program are presented. They indicate that magnetospheric ions of all species steadily escape into the magnetosheath and stream away from the magnetopause, regardless of the magnetosheath magnetic field orientation. It is concluded that the leakage model explains both the new and old observations at least as well as, or better than, the merging model.

Sibeck, D. G.↗
NASA NTRS1991

Volcanic aerosols: Chemistry, evolution, and effects

Stratospheric aerosols have been the subject of scientific speculation since the 1880s, when the powerful eruption of Krakatoa attracted worldwide attention to the upper atmosphere through spectacular optical displays. The presence of a permanent tenuous dust layer in the lower stratosphere was postulated in the 1920s following studies of the twilight glow. Junge collected the first samples of these 'dust' particles and demonstrated that they were actually composed of sulfates, most likely concentrated sulfuric acid (Junge and Manson, 1961; Junge, 1963). Subsequent research has been spurred by the realization that stratospheric particles can influence the surface climate of earth through their effects on atmospheric radiation. Such aerosols can also influence, through chemical and physical effects, the trace composition of the atmosphere, ozone concentrations, and atmospheric electrical properties. The properties of stratospheric aerosols (both the background particles and those enhanced by volcanic eruptions) were measured in situ by balloon ascents and high altitude aircraft sorties. The aerosols were also observed remotely from the ground and from satellites using both active (lidar) and passive (solar occultation) techniques (remote sensing instruments were carried on aircraft and balloon platforms as well). In connection with the experimental work, models were developed to test theories of particle formation and evolution, to guide measurement strategies, to provide a means of connecting laboratory and field data, and to apply the knowledge gained to answer practical questions about global changes in climate, depletion of the ozone layer, and related environmental problems.

Turco, Richard↗
NASA NTRS1992

Synoptic/planetary-scale interactions and blocking over the North Atlantic Ocean

The work completed under this grant represents a continuing investigation of synoptic/planetary-scale interactions over the North Atlantic Ocean in late Jan. 1979. The focus of attention was a blocking episode that developed over southern Greenland on 21 Jan. However, the diagnosis also extended to antecedent cyclone activity and the role of moist processes during wave development. In all, the project was partitioned into two phases: (1) an extension of diagnoses that were already in progress of the 21 Jan. blocking episode and its antecedent cyclone activity using satellite-enhanced level 3-b NASA/Goddard Laboratory for Atmospheres (GLA) analyses; and (2) an analysis of the extent to which the results of Phase 1 are sensitive to the presence of satellite information.

Smith, Phillip J.↗
NASA NTRS1991

Colorado Center for Astrodynamics Research (CCAR)

Viewgraphs on the Colorado Center for Astrodynamics Research (CCAR) are presented. Topics covered include: EOSDIS testbed: an Advanced Very High Resolution Radiometer (AVHRR) data system for snowpack and vegetation studies; satellite data processing software; satellite data analysis activities; mass storage systems; wide area network connections; and remote access.

Emery, William↗
NASA NTRS1993

The Oriented Scintillation Spectrometer Experiment - Instrument description

The Oriented Scintillation Spectrometer Experiment on the Arthur Holly Compton Gamma Ray Observatory satellite uses four actively shielded NaI (Tl)-CsI(Na) phoswich detectors to provide gamma-ray line and continuum detection capability in the 0.05-10 MeV energy range. The instrument includes secondary capabilities for gamma-ray and neutron detection between 10 and 250 MeV. The detectors have 3.8 deg x 11.04 deg (FWHM) fields of view defined by tungsten collimators. Each detector has an independent, single-axis orientation system which permits offset pointing from the spacecraft Z-axis for background measurements and multitarget observations. The instrument, and its calibration and performance, are described.

Johnson, W. N.↗
NASA NTRS1993

ENVISAT ASAR

This document is a series of viewgraphs on the Envisat advanced synthetic aperture radar (ASAR). Viewgraphs cover mission objectives, modes of operation, instrument parameters, a comparison with the European Remote Sensing Satellite (ERS-1) active microwave instrument (AMI), instrument design, transmit/receive module and antenna tile specifications, data rates, swath coverage, and ASAR program schedule.

Louet, Jacques↗
NASA NTRS1992

FITS data conversion efforts at the Compton Observatory Science Support Center

The Compton Gamma Ray Observatory (CGRO) is an active, earth orbiting satellite consisting of four gamma-ray telescopes. Each telescope is maintained by an independent principal investigator (PI) team, and each PI team has devised separate data formats to handle the needs of their particular instrument. As mandated by NASA, the Compton Observatory Science Support Center (COSSC) intends to archive and distribute PI data to the public in FITS (Flexible Image Transport System) format. To accomplish this task, we at COSSC have been developing a set of general purpose software tools that facilitate the transformation of non-FITS formatted data into FITS format. These tools, known as ToFU (To FITS Utilities), serve as the kernel of our CGRO data conversion software. This presentation describes the problems encountered in transcribing large amounts of data into a standard FITS form and the capabilities of the COSSC-built conversion software designed to perform the transformations.

Jennings, D. G.↗
NASA NTRS1995

DS-CDMA satellite diversity reception for personal satellite communication: Downlink performance analysis

The downlink of a satellite-mobile personal communication system employing power-controlled Direct Sequence Code Division Multiple Access (DS-CDMA) and exploiting satellite-diversity is analyzed and its performance compared with a more traditional communication system utilizing single satellite reception. The analytical model developed has been thoroughly validated by means of extensive Monte Carlo computer simulations. It is shown how the capacity gain provided by diversity reception shrinks considerably in the presence of increasing traffic or in the case of light shadowing conditions. Moreover, the quantitative results tend to indicate that to combat system capacity reduction due to intra-system interference, no more than two satellites shall be active over the same region. To achieve higher system capacity, differently from terrestrial cellular systems, Multi-User Detection (MUD) techniques are likely to be required in the mobile user terminal, thus considerably increasing its complexity.

DeGaudenzi, Riccardo↗
NASA NTRS1996

Analysis of EUVE Experiment Results

A series of tests to validate an antenna pointing concept for spin-stabilized satellites using a data relay satellite are described. These tests show that proper antenna pointing on an inertially-stabilized spacecraft can lead to significant access time through the relay satellite even without active antenna pointing. We summarize the test results, the simulations to model the effects of antenna pattern and space loss, and the expected contact times. We also show how antenna beam width affects the results.

Horan, Stephen↗