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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 289 records · Page 16
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NASA NTRS1985

CNPq/INPE-LANDSAT system

The current status of the Brazilian LANDSAT facilities operated by Instituto de Pesquisas Espaciais (INPE) and the results achieved during the period from October 1, 1984 to August 31, 1985 are presented. INPE's Receiving Station at Cuiaba, MT, operates normally the two tracking and receiving systems it has installed, the old one (1973) for Band S and the new one (February 1983) for dual S- and X-band. Both MSS and TM recording capabilities are functional. Support to the NASA Backup Plan for MSS data also remains active. Routine recordings are being made for LANDSAT-5 only, for both MSS and TM. Originally, MSS was recorded over the full acquisition range. However, since December, 1984, due to further reduction of operational expenses, both instruments are being recorded over Brazilian territory only.

Debarrosaguirre, J. L.↗
NASA NTRS1986

Effects of specimen preparation on the electromagnetic property measurements of solid materials with an automatic network analyzer

Effects of specimen preparation on measured values of an acrylic's electomagnetic properties at X-band microwave frequencies, TE sub 1,0 mode, utilizing an automatic network analyzer have been studied. For 1 percent or less error, a gap between the specimen edge and the 0.901-in. wall of the specimen holder was the most significant parameter. The gap had to be less than 0.002 in. The thickness variation and alignment errors in the direction parallel to the 0.901-in. wall were equally second most significant and had to be less than 1 degree. Errors in the measurement f the thickness were third most significant. They had to be less than 3 percent. The following parameters caused errors of 1 percent or less: ratios of specimen-holder thicknesses of more than 15 percent, gaps between the specimen edge and the 0.401-in. wall less than 0.045 in., position errors less than 15 percent, surface roughness, hickness variation in the direction parallel to the 0.401-in. wall less than 35 percent, and specimen alignment in the direction parallel to the 0.401-in. wall mass than 5 degrees.

Long, E. R., Jr.↗
NASA NTRS1986

Deep space network radio science system for Voyager Uranus and Galileo missions

An overview is presented of major new requirements, challenges and conceptual designs for the DSN Radio Science System in the 1985 to 1988 period. The Voyager Uranus encounter is being supported with larger combined aperture, higher sample rate, and a centrally controlled network. The Galileo mission will be provided with a high resolution S-Band Faraday rotation detection capability and a high-stability Doppler system with X-Band uplink for gravitational wave search.

Peng, T. K.↗
NASA NTRS1986

The Giotto radio-science experiment

The scientific objectives of the Giotto Radio Science Experiment (GRE) are to determine the columnar electron content of Comet Halley/s ionosphere and the cometary mass fluence from atmospheric drag by using the radio signals from Giotto during the Halley encounter. The radio science data (S and X-band Doppler and range measurements) will be collected at NASA/s deep-space 64 m tracking antenna at Tidbinbilla near Canberra, in Australia. In order to separate the effects of the terrestrial ionosphere and the interplanetary plasma, S-band Doppler measurements will also be taken at Tidbinbilla along the line-of-sight of Japan/s cometary probe Sakigake during the Giotto-Halley Encounter. The measurements of cometary electron content and mass fluence will be inverted to derive the spatial distribution of the electron and mass (dust and gas) density within Halley/s coma. The GRE is the only experiment on Giotto capable of measuring the low-energy (10 eV) electron bulk population of Halley/s ionosphere and the total cometary mass flow impacting upon the spacecraft.

Edenhofer, P.↗
NASA NTRS1985

The use of radar and visual observations to characterize the surface structure of the planet Mercury

An analysis is conducted of available topographic profiles and scattering parameters derived from earth-based S- and X-band radar observations of Mercury, in order to determine the nature and origin of regional surface variations and structures that are typical of the planet. Attention is given to the proposal that intercrater plains on Mercury formed from extensive volcanic flooding during bombardment, so that most craters were formed on a partially molten surface and were thus obliterated, together with previously formed tectonic features.

Clark, P. E.↗
NASA NTRS1986

Spacecraft technology requirements for future NASA missions

Missions selected by NASA as representative of the most critical technology issues are described and the key technology requirements are discussed. The following are considered: (1) the Large Deployable Reflector (LDR), (2) the Sample Return Missions (SRM), (3) the Earth Observing System (EOS), and (4) the Geostationary Communications Platform (GCP). The LDR, designed for infrared and submillimeter astronomical measurements, will contain the following components for its instruments: indium antimonide charge-coupled arrays, extrinsic photodetector arrays, and heterodyne photoconductors. New technology developed for SRM includes an X-band transponder, a fiber-optic rotation sensor, and long-life batteries. The EOS will consist of instruments designed to measure the earth's atmosphere, interior, and surface, as well as an information system to support scientific research. Inherent in the platform of the GCP is the ability to effectively utilize both the geostationary arc and the electromagnetic spectrum; the GCP can also reduce overall satellite communications system costs.

Hudson, W. R.↗
NASA NTRS1986

The Venus radar mapper spacecraft design

This paper discusses the driving mission requirements on the VRM spacecraft, the resulting design, and the spacecraft performance capabilities. The spacecraft design is driven by fine pointing requirements for radar mapping resolution, by extremes of thermal environment in the Venus orbit, and by high instrument power requirements. The spacecraft design emphasized use of as much existing hardware and software as possible to meet the cost constraints. Existing design was used where hardware was not already available. The VRM spacecraft utilizes the spare Voyager High Gain Antenna (HGA) and equipment bus, the Galileo computers and power conditioning equipment, and Mariner Medium Gain Antenna (MGA). Further cost savings were possible by using the HGA for both radar mapping at S-band frequency and high rate data playback at X-band frequency. The use of the Star 48 B solid rocket motor for VOI reduced propulsion system cost and complexity. The design tradeoffs that led to the VRM spacecraft configuration and the performance capabilities of the spacecraft are summarized for each subsystem.

Gamber, T.↗
NASA NTRS1986

PPM/NAR 8.4-GHz noise temperature statistics for DSN 64-meter antennas, 1982-1984

From August 1982 through November 1984, X-band downlink (8.4-GHz) system noise temperature measurements were made on the DSN 64-m antennas during tracking periods. Statistics of these noise temperature values are needed by the DSN and by spacecraft mission planners to assess antenna, receiving, and telemetry system needs, present performance, and future performance. These measurements were made using the DSN Mark III precision power monitor noise-adding radiometers located at each station. It is found that for DSS 43 and DSS 63, at the 90% cumulative distribution level, equivalent zenith noise temperature values fall between those presented in the earlier (1977) and present (1983) versions of DSN/Flight Project design documents. Noise temperatures measured for DSS 14 (Goldstone) are higher than those given in existing design documents and this disagreement will be investigated as a diagnostic of possible PPM or receiving system performance problems.

Slobin, S. D.↗
NASA NTRS1986

Propagation through Martian dust at 8.5 and 32 GHz

Independent studies of attenuation of X-band (8.5 GHz) and Ka-band (32 Ghz) radio signals when traversing Martian dust were carried out. These analyses turned out remarkably similar. The computational method is essentially that of T. S. Chu but uses observed optical depth at 0.67 microns rather than visibility as the measure of optical attenuation from which to derive the microwave attenuation. An awkwardness in the approach is that the size distribution of Martian dust particles is not well known, but the mean is probably around 4 microns, whereas in the terrestrial case it is nearer 10 microns. As a consequence, there will be a larger tail of particles still in the Mie regime in the Martian case as compared to the terrestrial one. The computational error will, therefore, be somewhat larger for Martian than Earth-bound dust. Fortunately, the indicated attenuations are small enough for the worst case (1.3 dB at 32 GHz) that the error is academic.

Smith, E. K.↗
NASA NTRS1986

The 60 GHz IMPATT diode development

The objective is to develop 60 GHz IMPATT diodes suitable for communications applications. The performance goals of the 60 GHz IMPATT is 1W CW output power with a conversion efficiency of 15 percent and 10-year lifetime. The final design of the 60 GHz IMPATT structure evolved from computer simulations performed at the University of Michigan. The initial doping profile, involving a hybrid double-drift (HDD) design, was derived from a drift-diffusion model that used the static velocity-field characteristics for GaAs. Unfortunately, the model did not consider the effects of velocity undershoot and delay of the avalanche process due to energy relaxation. Consequently, the initial devices were oscillating at a much lower frequency than anticipated. With a revised simulation program that included the two effects given above, a second HDD profile was generated and was used as a basis for fabrication efforts. In the area of device fabrication, significant progress was made in epitaxial growth and characterization, wafer processing, and die assembly. The organo-metallic chemical vapor deposition (OMCVD) was used. Starting with a baseline X-Band IMPATT technology, appropriate processing steps were modified to satisfy the device requirements at V-Band. In terms of efficiency and reliability, the device requirements dictate a reduction in its series resistance and thermal resistance values. Qualitatively, researchers were able to reduce the diodes' series resistance by reducing the thickness of the N+ GaAs substrate used in its fabrication.

Dat, Rovindra↗
NASA NTRS1987

Proposed upgrade of the Deep Space Network research and development station

Continued exploration of the solar system will require continued evolution of capabilities to support deep space communication and navigation. That evolution will rely, as it has in the past, on the development, demonstration, and field testing of communication and navigation technologies. The existing Deep Space Network (DSN) research and development station, DSS 13, at the Venus site, Goldstone, California was instrumental in those prior developments. However, the present antenna is no longer able to provide the necessary support for technology. The 26 meter antenna has good performance at S-band, fair performance at X-band, but is unusable at the anticipated Ka-band. It is not suitable for conversion to beam waveguides, and is not usable as a test bed for demonstrating high efficiency because of structural pliancy. Additionally, its size and age are increasingly a liability in demonstrations. A 34 meter beam waveguide version of the existing DSN high efficiency (HEF) antennas was proposed for FY-88 Construction of Facilities budget. The antenna is to be built at the Venus site, adjacent to the old antenna, and serve as the DSN research and development antenna through the end of the century.

Smith, Joel G.↗
NASA NTRS1987

Goldstone radar observations of Mars: The 1986 opposition

Radar echoes from the planet Mars were obtained on 27 S-band (wavelength = 12.5 cm) and 2 X-band (wavelength = 3.5 cm) tracks using the Goldstone Solar System Radar. These observations took advantage of the favorable 1986 opposition since the Earth-Mars distance was 0.40 AU at opposition and radar echo strength is proportional to inverse-fourth-power of the distance to the target. The coverages of the Goldstone observations are summarized. The observations were conducted via the CW-spectra techniques described by Harmon et al. A continuous tone was transmitted at Mars and the radar echo was sampled to obtain a Doppler spread spectrum. Each received event was separated into polarized (opposite sense circular) and depolarized (same sense circular) periods. There was one successful ranging run which had a resolution of 2 microseconds. This should yield surface heights accurate to 300 meters.

Thompson, T. W.↗
NASA NTRS1986

Dust distribution of Comet Halley from the Giotto radio science experiment

Measurements from the Giotto radio science experiment representing the Doppler frequency shift and the intensity level of the X-band downlink signal of the Giotto spacecraft during its encounter with comet Halley are shown. Continuous data reception was maintained throughout the encounter. The Doppler shift measured within a time interval of 100 sec is due to drag effects in the cometary atmosphere causing a deceleration of the spacecraft. The total change of velocity of Giotto is 23.2 cm/sec resulting in a best estimate of 0.32 g for the total cometary mass impacting Giotto during the Halley flyby. A dust jet structure for the inner coma of comet Halley is derived. Several sharply confined dust jets are distinguishable; for the most prominent one, characteristic properties are deduced. Features of this jet structure are shown to correlate with measurements from on-board Giotto experiments and with Earth-based observations.

Edenhofer, P.↗
NASA NTRS1987

Compound-taper feedhorn for the DSN 70-meter antennas

A novel X-band feedhorn was designed for the Deep Space Network (DSN) 70-meter antennas. The feedhorn is a compound-taper structure consisting of a corrugated flared section and a corrugated straight section. This feedhorn is designed to closely initiate the characteristics of the standard feedhorn, while providing the proper phase center location, without adding any significant loss to the system. The use of the existing feedhorn and the ease of manufacturing the corrugated straight section have resulted in major overall cost savings.

Manshadi, F.↗
NASA NTRS1987

Modeling the interactions between the ocean and the environment for microwave radar sensing

An extensive set of X-band microwave backscatter measurements has been analyzed to determine its dependence on winds near the surface, atmospheric stability, and long-wave slopes. These radar measurements, made from a tower in the Gulf of Mexico, were performed in conjunction with an extensive set of simultaneous environmental measurements. The CW microwave system operated at an incidence angle of 45 deg, with antennas directed into winds and waves. Model functions for the radar cross section (RCS) and the modulation transfer function (MTF) are developed that depend on the geophysical variables, including wind stress. Statistical analysis shows that these models functions yield a significant smaller error when fit to the RCS data than a simple wind-speed function displays. A Taylor-series expansion of the returned power from a small area provides a unified function that demonstrates the complementary roles of wave slope and atmospheric fluctuations on both the RCS, the MTF, and the coherence. The issue of linearity of the MTF is addressed with this data set, yielding evidence that this is a valid assumption. These results have direct application to the remote sensing of the mean and fluctuating winds, and the wave spectrum with coherent and incoherent active radars.

Weissman, David E.↗
NASA NTRS1986

The Earth Observing System (EOS) synthetic aperture radar (SAR)

The evolution of the Spaceborne Imaging Radar (SIR) has led to a multipolarization, multifrequency SAR with variable imaging geometry which will be ready for flight on the Space Station Earth Observing System (EOS). Nominally, this SAR will be a three-frequency (L-, C-, and X-band) system with quad polarization available for the L and C bands. It will be capable of acquiring multiincidence-angle data using electronic beam steering, and other imaging geometries by mechanically pitching, yawing, and rolling the antenna. The capabilities of the EOS SAR, particularly acquisition of cross-polarized and high-incidence-angle data, depend on the altitude of the platform on which the SAR flies and improve significantly at lower altitudes. The EOS SAR will provide a unique new data set and will play a key role in understanding the earth's global processes, alone and synergistically with other EOS instruments.

Cimino, Jobea↗
NASA NTRS1987

The atmosphere of Uranus - Results of radio occultation measurements with Voyager 2

The Uranian atmosphere is investigated on the basis of S-band and X-band occultation observations (including measurements of Doppler frequency perturbations) obtained during the Voyager 2 encounter with Uranus in January 1986. The data are presented in extensive tables and graphs and characterized in detail. The atmosphere is assumed to have an H2/He abundance ratio of about 85/15, but also to contain small amounts of CH4 at above-cloud relative humidity 30 percent, cloud-base relative humidity 78 percent, and below-cloud mixing ratio 2.3 percent by number density. Other parameters estimated include magnetic-field rotation period 17.24 h, 1-bar equatorial radius 25,559 + or - 4 km, polar radius 24,973 + or - 20 km, equatorial acceleration of gravity 8.69 + or - 0.01 m/sec sq, and atmospheric temperature 76 + or - 2 K (assuming 85 + or - 3 percent H2).

Lindal, G. F.↗
NASA NTRS1996

Science Results from the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR): Progress Report

The Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar (SIR-C/X-SAR) is the most advanced imaging radar system to fly in Earth orbit. Carried in the cargo bay of the Space Shuttle Endeavour in April and October of 1994, SIR-C/X-SAR simultaneously recorded SAR data at three wavelengths (L-, C-, and X-bands; 23.5, 5.8, and 3.1 cm, respectively). The SIR-C/X-SAR Science Team consists of 53 investigator teams from more than a dozen countries. Science investigations were undertaken in the fields of ecology, hydrology, ecology, and oceanography. This report contains 44 investigator team reports and several additional reports from coinvestigators and other researchers.

Diane L Evans↗