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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 145 records · Page 8
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NASA NTRS1974

Some economic benefits of a synchronous earth observatory satellite

An analysis was made of the economic benefits which might be derived from reduced forecasting errors made possible by data obtained from a synchronous satellite system which can collect earth observation and meteorological data continuously and on demand. User costs directly associated with achieving benefits are included. In the analysis, benefits were evaluated which might be obtained as a result of improved thunderstorm forecasting, frost warning, and grain harvest forecasting capabilities. The anticipated system capabilities were used to arrive at realistic estimates of system performance on which to base the benefit analysis. Emphasis was placed on the benefits which result from system forecasting accuracies. Benefits from improved thunderstorm forecasts are indicated for the construction, air transportation, and agricultural industries. The effects of improved frost warning capability on the citrus crop are determined. The benefits from improved grain forecasting capability are evaluated in terms of both U.S. benefits resulting from domestic grain distribution and U.S. benefits from international grain distribution.

Battacharyya, R. K.↗
NASA NTRS1972

Interferometric observations of an artificial satellite.

Very-long-baseline interferometric observations of radio signals from the TACSAT synchronous satellite, even though extending over only 7 hours, have enabled an excellent orbit to be deduced. Precision in differential delay and delay-rate measurements reached 0.15 nanosecond and 0.05 picosecond per second, respectively. The results from this initial three-station experiment demonstrate the feasibility of using the method for accurate satellite tracking and for geodesy.

Preston, R. A.↗
NASA NTRS1974

Synchronous Earth Observatory Satellite /SEOS/

NASA/GSFC is currently studying the applications and technical requirements for a Synchronous Earth Observations Satellite (SEOS). Such a satellite would combine the relatively high resolution and multi-spectral capability of the Earth Resources Technology Satellite (ERTS) with the on-station continuous monitoring of the Synchronous Meteorological Satellite (SMS). SEOS capability is geared to perform disaster warning of tornadoes and floods as well as to monitor transient phenomena affecting earth resources (e.g., green waves and algae blooms). The heart of the system is a Large Earth Survey Telescope (LEST) which has a designed 1.5 meter diameter. Spectral bands in the visible, near- and far-infrared have been selected to optimize SEOS utility. A microwave sounder will be used in conjunction with the LEST for meteorological applications.

Walter, L. S.↗
NASA NTRS1972

A north-south stationkeeping ion thruster system for ATS-F.

An ion thruster system is being developed for the ATS-F satellite to demonstrate the application of ion thruster technology to the synchronous satellite north-south stationkeeping mission. The cesium bombardment ion thruster develops one millipound thrust at 2600 seconds specific impulse and provides thrust vectoring by accelerator electrode displacement. The propellant system is sized for two years operation at 25 percent duty cycle. Power conditioning circuitry is based on transistor inverters switching at 10 kHz. Thirteen command channels allow flexibility in operation; 12 telemetry channels provide information on system performance. Input power is less than 150 watts.

Worlock, R.↗
NASA NTRS1973

A north-south stationkeeping ion thruster system for ATS-F

A one millipound cesium ion thruster system experiment designed for the ATS-F satellite will be used to demonstrate north-south stationkeeping for synchronous satellites. Development effort leading to the present design will be described and test data for qualification and flight acceptance tests will be presented. These include a review of EMI evaluations tests made with the power conditioning subsystem and the thruster simulator, and an extended system operational test. During the extended test, 90 on-off cycles simulated thruster operation in orbit. A planned 18,000 hour ground test of a flight qualified thruster will be discussed.

James, E.↗
NASA NTRS1972

Unmanned spacecraft for research

The applications of unmanned spacecraft for research purposes are discussed. Specific applications of the Communication and Navigation satellites and the Earth Observations satellites are described. Diagrams of communications on world-wide basis using synchronous satellites are developed. Photographs of earth resources and geology obtained from space vehicles are included.

Graves, C. D.↗
NASA NTRS1982

Cloud cover sampling capability of various satellite combinations for ISCCP

One of the most important objectives of the International Satellite Cloud Climatology Project (ISCCP) is the quantification of cloud cover and associated radiation parameters for climate research. The time-varying nature of cloud cover requires a measurement system that obtains cloud radiance at sufficient time intervals for determining accurate values of cloudiness for the appropriate averaging period. Current plans for the ISCCP call for such day to be acquired every 3 hours during both data and night to ensure that the diurnal cycle of cloud cover is adequately sampled. The satellite system proposed is an array of geostationary and polar-orbiting satellites. The error in mean cloud cover estimates for observation systems which do not include geostationary satellites are quantified. Candidates for such a system include two NOAA Sun-synchronous satellites with daylight equatorial-crossing times of 0730 and 1430, and a USSR satellite in an 81 deg. inclination, 900-km altitude orbit.

Harrison, E. F.↗
NASA NTRS1991

Satellite orbit considerations for a global change technology architecture trade study

A study was conducted to determine satellite orbits for Earth observation missions aimed at obtaining data for assessing global climate change. A multisatellite system is required to meet the scientific requirements for temporal coverage over the globe. The best system consists of four Sun-synchronous satellites equally spaced in local time of equatorial crossing. This system can obtain data every three hours for all regions. Several other satellite systems consisting of combinations of Sun-synchronous orbits and either the Space Station Freedom or a mid-latitude equatorial satellite can provide three to six hour temporal coverage, which is sufficient for measuring many of the parameters required for the global change monitoring mission. Geosynchronous satellites are required to study atmospheric and surface processes involving variations on the order of a few minutes to an hour. Two or more geosynchronous satellites can be relocated in longitude to study processes over selected regions of Earth.

Harrison, Edwin F.↗
NASA NTRS1991

Satellite orbit considerations for a global change technology architecture trade study

A study was conducted to determine satellite orbits for earth observation missions aimed at obtaining data for assessing data global climate change. A multisatellite system is required to meet the scientific requirements for temporal coverage over the globe. The best system consists of four sun-synchronous satellites equally spaced in local time of equatorial crossing. This system can obtain data every three hours for all regions. Several other satellite systems consisting of combinations of sun-synchronous orbits and either the Space Station Freedom or a mid-altitude equatorial satellite can provide three to six hour temporal coverage, which is sufficient for measuring many of the parameters required for the global change monitoring mission. Geosynchronous satellites are required to study atmospheric and surface processes involving variations on the order of a few minutes to an hour. One or two geosynchronous satellites can be relocated in longitude to study processes over selected regions of earth.

Harrison, Edwin F.↗
NASA NTRS1984

Comparison of longwave diurnal models applied to simulations of the Earth Radiation Budget Experiment

The Earth Radiation Budget Experiment (ERBE) is a multisatellite experiment which is to be implemented in the mid 1980s. The experiment involves a utilization of instruments on one or more sun-synchronous satellites in the NOAA series, and the employment of a dedicated spacecraft, the ERBS, in a 57 deg orbit. One of the objectives of ERBE is related to an improvement of knowledge regarding the diurnal variability in the earth's radiation balance. In the present investigation, satellite samples of longwave (LW) radiation over land are simulated for both sun-synchronous and non-sun-synchronous orbits. Three different LW diurnal models are then applied to the sampled data, and the resulting modeled monthly net LW radiant exitances are compared against reference values based on complete hourly sampling of the area for a month. The results demonstrate the general usefulness of a trigonometric diurnal LW model for land regions with daytime heating trends.

Brooks, D. R.↗
NASA NTRS1976

Simulation of radiometer data from a spin stabilized satellite

The effect of misregistration on cloud brightness threshold is investigated by simulating radiometric data as observed from a spin stabilized synchronous satellite such as the SMS. Clouds were introduced randomly and a bidirectional reflectance model was used to create radiance data from clouds and ocean. A theoretical and an empirical reflectance model were compared.

Rangaswamy, S.↗
NASA NTRS1975

Results of the 3 November 1974 Applications Technology Satellite-6 (ATS-6) trilateration test

The highly successful 24 hour trilateration tracking and orbit determination test conducted on 3 November 1974 is described. In this test a new method of accurately computing geostationary spacecraft orbits was applied to the Applications Technology Satellite (ats-6). A single tracking station interrogates several strategically deployed ground based transponders via the synchronous satellite whose orbit is to be determined. The ATS-6 tracking data measurement noise over the 24 hour period was observed to be 0.3 mm/sec in range rate and 1.5 meters in range. By means of overlap orbit computation using 2 separate tracking data bases, the ATS-6 total position and velocity uncertainties were determined to reach a minimum of 30 meters and 0.2 cm/sec respectively. The maximum position and velocity uncertainty over this same time period was determined to be approximately 250 meters and 2 cm/sec respectively. A position determination using simultaneous tracking of the NASA-GSFC site by ATS-6 and ATS-3 was also performed. Station location recovery was to an accuracy on the order of 100 meters over the first 10 hours of tracking.

Schmid, P. E.↗
NASA NTRS1994

Gravity model improvement using the DORIS tracking system on the SPOT 2 satellite

A high-precision radiometric satellite tracking system, Doppler Orbitography and Radio-positioning Integrated by Satellite system (DORIS), has recently been developed by the French space agency, Centre National d'Etudes Spatiales (CNES). DORIS was designed to provide tracking support for missions such as the joint United States/French TOPEX/Poseidon. As part of the flight testing process, a DORIS package was flown on the French SPOT 2 satellite. A substantial quantity of geodetic quality tracking data was obtained on SPOT 2 from an extensive international DORIS tracking network. These data were analyzed to assess their accuracy and to evaluate the gravitational modeling enhancements provided by these data in combination with the Goddard Earth Model-T3 (GEM-T3) gravitational model. These observations have noise levels of 0.4 to 0.5 mm/s, with few residual systematic effects. Although the SPOT 2 satellite experiences high atmospheric drag forces, the precision and global coverage of the DORIS tracking data have enabled more extensive orbit parameterization to mitigate these effects. As a result, the SPOT 2 orbital errors have been reduced to an estimated radial accuracy in the 10-20 cm RMS range. The addition of these data, which encompass many regions heretofore lacking in precision satellite tracking, has significantly improved GEM-T3 and allowed greatly improved orbit accuracies for Sun-synchronous satellites like SPOT 2 (such as ERS 1 and EOS). Comparison of the ensuing gravity model with other contemporary fields (GRIM-4C2, TEG2B, and OSU91A) provides a means to assess the current state of knowledge of the Earth's gravity field. Thus, the DORIS experiment on SPOT 2 has provided a strong basis for evaluating this new orbit tracking technology and has demonstrated the important contribution of the DORIS network to the success of the TOPEX/Poseidon mission.

Nerem, R. S.↗