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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Radar image processing of real aperture SLAR data for the detection and identification of iceberg and ship targets

An iceberg detection and identification system consisting of a moderate resolution Side Looking Airborne Radar (SLAR) interfaced with a Radar Image Processor (RIP) based on a ROLM 1664 computer with a 32K core memory updatable to 64K is described. The system can be operated in high- or low-resolution sampling modes. Specifically designed algorithms are applied to digitized signal returns to provide automatic target detection and location, geometrically correct video image display and data recording. The real aperture Motorola AN/APS-94D SLAR operates in the X-band and is tunable between 9.10 and 9.40 GHz; its output power is 45 kW peak with a pulse repetition rate of 750 pulses per hour. Schematic diagrams of the system are provided, together with preliminary test data.

Marthaler, J. G.↗
NASA NTRS1979

Initial observations of the nightside ionosphere of Venus from Pioneer Venus Orbiter radio occultations

Results of radio occultation measurements of electron density profiles of the nightside ionosphere of Venus at solar zenith angles from 90 to 164 deg, obtained from the Pioneer Venus Orbiter, are reported. Data were derived from closed-loop S- and X-band signals received by the Deep Space Network upon ionospheric entry and exit of the spacecraft. Nightside electron density profiles are found to be rather uniform in the solar zenith angle range of from 95 to 107 deg, with peak electron densities ranging from 23,000 to 40,000/cu cm, while between 110 and 164 deg, profiles exhibit a high degree of variability and peak electron densities vary from 7,600 to 31,800/cu cm. A possible mechanism for the maintenance of the nightside Venus ionosphere during the long Venus night, which is consistent with the observed spatial and temporal variability of deep ionospheric electron density profiles, is proposed to be impact ionization by precipitating particles, although transport processes from the dayside may also be important.

Kliore, A. J.↗
NASA NTRS1980

Radio propagation through solar and other extraterrestrial ionized media

The present S- and X-band communications needs in deep space are addressed to illustrate the aspects which are affected by propagation through extraterrestrial plasmas. The magnitude, critical threshold, and frequency dependence of some eight propagation effects for an S-band propagation path passing within 4 solar radii of the Sun are described. The theory and observation of propagation in extraterrestrial plasmas are discussed and the various plasma states along a near solar propagation path are illustrated. Classical magnetoionic theory (cold anisotropic plasma) is examined for its applicability to the path in question. The characteristics of the plasma states found along the path are summarized and the errors in some of the standard approximations are indicated. Models of extraterrestrial plasmas are included. Modeling the electron density in the solar corona and solar wind, is emphasized but some cursory information on the terrestrial planets plus Jupiters is included.

Smith, E. K.↗
NASA NTRS1980

Planetary radar

The radar astronomy activities supported by the Deep Space Network are reported. The high power S- and X-band radar transmitters at the Goldstone 64 meter station were used for a radar probe of Mars during January, February, and March 1980, which was designed to provide range and Doppler data derived from signals reflected from the Martian surface, taking advantage of the planet's nearness during opposition.

Taylor, R. M.↗
NASA NTRS1980

Heterodyne detection of the 752.033-GHz H2O rotational absorption line

A tunable high resolution two stage heterodyne radiometer was developed for the purpose of investigating the intensity and lineshape of the 752.033 GHz rotational transition of water vapor. Single-sideband system noise temperatures of approximately 45,000 K were obtained using a sensitive GaAs Schottky diode as the first stage mixer. First local oscillator power was supplied by a CO2 laser pumped formic acid laser (761.61 GHz), generating an X-band IF signal with theoretical line center at 9.5744 GHz. Second local oscillator power was provided by means of a 3 GHz waveguide cavity filter with only 9 dB insertion loss. In absorption measurements of the H2O taken from a laboratory simulation of a high altitude rocket plume, the center frequency of the 752 GHz line was determined to within 1 MHz of the reported value. A rotational temperature 75 K, a linewidth 5 MHz and a Doppler shift 3 MHz were measured with the line-of-sight intersecting the simulated-plume axis at a distance downstream of 30 nozzle diameters. These absorption data were obtained against continuum background radiation sources at temperatures of 1175 and 300 K.

Dionne, G. F.↗
NASA NTRS1980

Use of K sub A-band for radio metric determinations

The use of K sub A-band to alleviate the radio metric degradation caused by charged particles is discussed. Those aspects of radio metrics which are relevant to the possible future use of K sub A-band deep space to Earth and Earth to deep space links are reviewed. In particular the effects of the Earth ionosphere, troposphere, and solar plasma are examined. It is concluded that, from the standpoint of reducing the harmful effects of charged particles, the use of K sub A-band appears highly desirable. While stability will be a more serious design constraint at K sub A-band than it is at X-band (for example in the ground power amplifier and the spacecraft multiplier stages) this problem is amenable to a state of the art engineering solution.

Potter, P. D.↗
NASA NTRS1980

A prelude to interstellar flight

A 20 to 50 year interstellar precursor mission extending 400 to 1000 AU from the solar system is outlined as a means of bringing out and solving engineering problems inherent in a star mission, and of studying the heliopause, the interstellar medium, and cosmic rays outside the heliosphere. Solar or laser sailing combined with a 500 kWe nuclear-electric propulsion system using fission would achieve a heliocentric excess velocity of 100km/s for the 32,000 kg spacecraft having a Shuttle derivative as a launch vehicle, and containing a Pluto flyby or separate orbiter powered by radioiosotope thermoelectric generators. X-band transmission using 40 w of power, a 15 m diameter spacecraft antenna and a 100 m receiving antenna on earth and providing 100 b/s is proposed, but a rate of 2 to 4 kb/s via 500 to 1000 w of power using the K-band and a 300 m diameter receiving antenna located on an Orbiting Deep Space Relay Station is also considered.

Jaffe, L. D.↗
NASA NTRS1979

Landsat-D data acquisition and processing

The Landsat-D system, in which S-band and X-band data links will provide real-time direct transmission of sensor data, is described. System performance objectives include input data quantity of 200 MSS scenes/day and 100 TM scenes/day by the Domestic Communication Satellite, and processing capability, in a pipeline mode, of 2.6 x 10 to the 11th input bits of sensor data per 16-hour day. Data processing techniques, including automated cloudcover assessment, control point library build system, radiometric calibration, and geometric correction are discussed.

Smith, P. L., Jr.↗
NASA NTRS1980

Viking Orbiter 75 in-flight pointing calibration of the high-gain antenna

An in-flight pointing calibration technique developed for the Viking Orbiter high-gain antenna has been validated through actual flight usage. The desired telecommunications performance dictated that the high-gain antenna pointing error be held at 0.7 deg, which would have been exceeded without calibration. The in-flight calibration methodology required the development of a stochastic model of the spacecraft rotational biases and earth-received signal strength measurements. The signal strength measurements, which were performed at X-band frequency, were used as observations to estimate the rotational biases and their corresponding uncertainties. Reducing the uncertainties of these parameters resulted in increased antenna pointing accuracy. The initial pointing offset was estimated to be in excess of 1 deg, and after in-flight calibration it was reduced to about 0.66 deg. About 50% of the original offset could not be calibrated, thus the improvement on the remaining offset is better than 50%.

Assefi, T.↗
NASA NTRS1980

A stable submillimeter laser local oscillator for heterodyne radiometry and spectroscopy

A submillimeter laser with off-axis pump beam injection is described. This design concept achieves complete isolation of the pump laser with respect to the pump radiation reflected from the submillimeter resonator. Active line independent stabilization of the pump laser is obtained by the use of an external tunable etalon as a frequency reference. The submillimeter output power is constant to within 4% over periods of hours. Mean frequency drifts of less than 2 parts in 100 million per minute were measured by mixing with very high harmonics of an X-band synthesizer in a planar Schottky diode.

Koepf, G. A.↗
NASA NTRS1980

Microwave radiometer measurements of soil moisture content

A unique set of radiometer measurements is presented, recorded during a 1000-h day and night monitoring of irrigated fields from fully saturated to completely dry. Radiometer measurements were recorded at 2.8-cm (X-band) and 21.4-cm (L-band) wavelengths for a range of incident angles from nadir to 50 deg. Soil moisture and soil temperature profile measurements were recorded to a depth of 15 cm. The test site was located in east-central Texas on a clay soil (Miller clay). Three bare-surface plots were used, each having a distinctly different surface roughness. Vegetated plots were also measured. The data quantify the sensitivity of microwave radiometer measurements to soil moisture variations, the effect of surface roughness on the measurement, and the influence of surface vegetation.

Newton, R. W.↗
NASA NTRS1980

The use of radar and LANDSAT data for mineral and petroleum exploration in the Los Andes region, Venezuela

A geological study of a 27,500 sq km area in the Los Andes region of northwestern Venezuela was performed which employed both X-band radar mosaics and computer processed Landsat images. The 3.12 cm wavelength radar data were collected with horizontal-horizontal polarization and 10 meter spatial resolution by an Aeroservices SAR system at an altitude of 12,000 meters. The radar images increased the number of observable suspected fractures by 27 percent over what could be mapped by LANDSAT alone, owing mostly to the cloud cover penetration capabilities of radar. The approximate eight fold greater spatial resolution of the radar images made possible the identification of shorter, narrower fractures than could be detected with LANDSAT data alone, resulting in the discovery of a low relief anticline that could not be observed in LANDSAT data. Exploration targets for petroleum, copper, and uranium were identified for further geophysical work.

Vincent, R. K.↗
NASA NTRS1980

Side-looking airborne radar image interpretation and geological mapping: Problems and results

Geological experiments and surveys conducted by BRGM and GDTA members to evaluate interest in SLAR image interpretation are summarized. Two surveys were selected for presentation: Les Vans (Massif central, France) and Guyana (South America). They have permitted a comparison between different types of SLAR: Goodyear, Motorola, JPL, and Vigie in term of lithological and structural applications. On the Les Vans test site conclusions reached concern radiometry, which is better on L-band imagery, polarization, HV being more useful than HH for geological mapping in an L-band system, wavelength and illuminations. Over Guyana, the use of Goodyear X-band SLAR enables satisfactory geological and structural mapping under heavy equatorial forest with cloud cover conditions. A differential program was developed for fracture filtering and image enhancement with a coherent light laser, and significant results were obtained.

Scanvic, J. Y.↗
NASA NTRS1980

Active retrodirective arrays for SPS beam pointing

The basic requirement of the SPS beam pointing system is that it deliver a certain amount of S-band (lambda = 12.5 cm) power to a 9.6 km diameter receiving rectenna on the ground. The power is transmitted from a 1.0 km diameter antenna array on the SPS, which is, for a rectenna at about plus or minus 40 deg. latitude, some 37.5x10 to the 6th power km distant. At the present time ARA's appear to be the best bet to realize this very stringent beam pointing requirement. An active retrodirective array (ARA) transmits a beam towards the apparent source of an illuminating signal called the pilot. The array produces, not merely reflects, RF power. Retrodirectivity is achieved by retransmitting from each element of the array a signal whose phase is the "conjugate" of that received by the element. Phase conjugate circuits and pointing errors in ARA's are described. Results obtained using a 2-element X-band ARA and an 8-element S-band ARA are included.

Chernoff, R.↗
NASA NTRS1980

An analysis of source structure effects in radio interferometry measurements

To begin a study of structure effects, this report presents a theoretical framework, proposes an effective position approach to structure corrections based on brightness distribution measurements, and analyzes examples of analytical and measured brightness distributions. Other topics include the effect of the frequency dependence of a brightness distribution on bandwidth synthesis (BWS) delay, the determination of the absolute location of a measured brightness distribution, and structure effects in dual frequency calibration of charged particle delays. For the 10 measured distributions analyzed, it was found that the structure effect in BWS delay at X-band (3.6 cm) can reach 30 cm, but typically falls in the range of 0 to 5 cm. A trial limit equation that is dependent on visibility was successfully tested against the 10 measured brightness distributions (seven sources). If the validity of this particular equation for an upper limit can be established for nearly all sources, the structure effect in BWS delay could be greatly reduced without supplementary measurements of brightness distributions.

Thomas, J. B.↗
NASA NTRS1982

A note on deep space optical communication link parameters

Topical communication in the context of a deep space communication link. Communication link analysis at the optical frequencies differs significantly from that at microwave frequencies such as the traditional S and X-bands used in deep space applications, due to the different technology of transmitter, antenna, modulators, and receivers. In addition, the important role of quantum noise in limiting system performance is quite different than that of thermal noise. The optical link design is put in a design control table format similar to a microwave telecom link design. Key considerations unique to the optical link are discussed.

Dolinar, S. J.↗
NASA NTRS1979

Evaluation of SLAR and thematic mapper MSS data for forest cover mapping using computer-aided analysis techniques

A literature review on radar and spectral band information was conducted and a NC-130 mission was flown carrying the NS001 scanner system which basically corresponds to the channel configuration of the proposed thematic mapper. Aerial photography and other reference data were obtained for the study site, an area approximately 290 sq miles in north central South Carolina. A cover type map was prepared and methods were devised for reformatting and geometrically correcting MSS CRT data. Arrangements were made to obtain LANDSAT data for dates approximating the NC-130 mission. Because of the waveband employed to obtain SEASAT radar data, it was decided to determine if X-band (2.40 cm to 3.75 cm wavelength) imagery is available.

Hoffer, R. M.↗
NASA NTRS1979

Full scale LANDSAT-D antenna pattern measurements

The design verification of the LANDSAT-D antenna subsystem is addressed. In particular, the analysis of the antenna radiation patterns utilizing a full scale mockup of the LANDSAT-D satellite is discussed. Test antennas included two S-Band shaped beam antennas, two S-Band omni unit radiators (to operate in array), a GPS antenna, an X-Band shaped beam antenna, and one S-Band high-gain parabolic antenna.

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