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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 91 records · Page 5
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NASA NTRS1974

Delta-102 Synchronous Meteorological Satellite (SMS-A): Operations summary

The Synchronous Meteorological Satellite (SMS) program is a joint effort of the National Aeronautics and Space Administration and the Department of Commerce. This program is intended to provide systematic worldwide weather coverage on an operational basis. The pilot SMS program is expected to launch three spacecraft: two prototype spacecraft designated SMS-A and SMS-B and one operational spacecraft designated SMS-C. The SMS program will use spacecraft in synchronous orbit to obtain day and night information on the earth's weather by means of earth imaging instruments, retransmission of image data, data collection, data relay, and space environmental monitoring.

Source record↗
NASA NTRS1985

The role of a low Earth orbiter in intercontinental time synchronization via GPS satellites

Time synchronization between two sites using differential GPS has been investigated by a number of researchers. When the two sites are widely separated, the common view period of any GPS satellite becomes shorter; low elevation observations are inevitable. This increase the corrupting effects of the atmospheric delay and, at the same time, narrows the window for such time synchronization. This difficulty can be alleviated by synchronization. This difficulty can be alleviated by using a transit site located midway between the two main sites. The main sites can now look at different GPS satellites which are also in view at the transit site. However, a ground transit site may not always be conveniently available, especially across the Pacific Ocean; also, the inclusion of a ground transit site introduce additional errors due to its location error and local atmospheric delay. An alternative is to use a low Earth orbiter (LEO) as the transit site. A LEO is superior to a ground transit site in three ways: (1) It covers a large part of the Earth in a short period of time and, hence, a single LEO provides worldwide transit services; (2) it is above the troposphere and thus its inclusion does not introduce additional tropospheric delay error; and (3) it provides strong dynamics needed to improve GPS satellite positions which are of importance to ultraprecise time synchronization.

Wu, S. C.↗
NASA NTRS1972

An amplitude-steered, electronically despun antenna for the synchronous meteorological satellite.

Description of the design and performance of a dual-band electronically despun, high-gain, earth-coverage satellite antenna for use on the Synchronous Meteorological Satellite. The SMS satellite is designed to take high-resolution cloud cover pictures from synchronous altitude. Several unique design features are described, including a scheme for steering energy around the array in a continuous fashion to avoid 'phase jumps' caused by sudden energy switches.

Dietrich, F. J.↗
NASA NTRS1975

Synchronous Meteorological Satellite spin testing

The end-to-end spin tests conducted on the Synchronous Meteorological Satellite are described in detail. It is noted that the objective of these tests was to demonstrate that the satellite performed its intended functions under spinning conditions and that all satellite functions were tested except for solar-panel illumination, pyrotechnic-device operation, VISSR infrared operation, and auxiliary propulsion-system operation. Tests discussed include antenna pointing, S-band and UHF equivalent isotropic radiated power, output-power ripple, bit error rate, synchronous electromagnetic interference, earth width measurement, and satellite magnetic-field measurement. The purpose, technique, salient results, and problems of each test are outlined.

Mcbrady, D. J.↗
NASA NTRS1992

Multi-access laser communications terminal

The Optical Multi-Access (OMA) Terminal is capable of establishing up to six simultaneous high-data-rate communication links between low-Earth-orbit satellites and a host satellite at synchronous orbit with only one 16-inch-diameter antenna on the synchronous satellite. The advantage over equivalent RF systems in space weight, power, and swept volume is great when applied to NASA satellite communications networks. A photograph of the 3-channel prototype constructed under the present contract to demonstrate the feasibility of the concept is presented. The telescope has a 10-inch clear aperture and a 22 deg full field of view. It consists of 4 refractive elements to achieve a telecentric focus, i.e., the focused beam is normal to the focal plane at all field angles. This feature permits image pick-up optics in the focal plane to track satellite images without tilting their optic axes to accommodate field angle. The geometry of the imager-pick-up concept and the coordinate system of the swinging arm and disk mechanism for image pick-up are shown. Optics in the arm relay the telescope focus to a communications and tracking receiver and introduce the transmitted beacon beam on a path collinear with the receive path. The electronic circuits for the communications and tracking receivers are contained on the arm and disk assemblies and relay signals to an associated PC-based operator's console for control of the arm and disk motor drive through a flexible cable which permits +/- 240 deg travel for each arm and disk assembly. Power supplies and laser transmitters are mounted in the cradle for the telescope. A single-mode fiber in the cable is used to carry the laser transmitter signal to the arm optics. The promise of the optical multi-access terminal towards which the prototype effort worked is shown. The emphasis in the prototype development was the demonstration of the unique aspect of the concept, and where possible, cost avoidance compromises were implemented in areas already proven on other programs. The design details are described in section 2, the prototype test results in section 3, additional development required in section 4, and conclusions in section 5.

Source record↗
NASA NTRS1971

Synchronous meteorological satellite system description document, volume 3

The structural design, analysis, and mechanical integration of the synchronous meteorological satellite system are presented. The subjects discussed are: (1) spacecraft configuration, (2) structural design, (3) static load tests, (4) fixed base sinusoidal vibration survey, (5) flight configuration sinusoidal vibration tests, (6) spacecraft acoustic test, and (7) separation and shock test. Descriptions of the auxiliary propulsion subsystem, the apogee boost motor, communications system, and thermal control subsystem are included.

Pipkin, F. B.↗
NASA NTRS1972

Synchronous meteorological satellite system description document, volume 4

The command and data acquisition (CDA) station for the Synchronous Meteorological Satellite (SMS) program, located on the Eastern shore of Virginia, is described in terms of facility layout, ground support instrumentation, and capabilities. Data systems and equipment are described in detailed block diagrams. The major subsystems are identified and information on equipment specifications, frequency ranges, and data processing format is given. Automatic picture transmission, data utilization stations, data collection platforms, and the various communication links from the CDA station to the SMS spacecraft are discussed.

Lahzun, J.↗
NASA NTRS2002

Differential Cratering of Synchronously Rotating Satellites by Ecliptic Comets

We use Monte Carlo methods to simulate impacts of ecliptic comets on the synchronously rotating satellites of giant planets. We reconfirm the long-standing prediction that the cratering rate should be much higher on the leading hemispheres than on the trailing hemisphere; indeed we find that previously published analytical formulations modestly underestimate the degree of apex-antapex asymmetry to be expected. We then compare our results to new mapping of impact craters on Ganymede, Callisto, and Triton. Ganymede reveals a pronounced apex-antapex asymmetry that is nonetheless much less than predicted. All of Triton's confirmed impact craters are clustered toward the apex of motion, far exceeding the predicted asymmetry. No asymmetry is observed on Callisto. In each case at least one of our basic assumptions must be wrong. Likely candidates include the following: (i) the surfaces of all but the most sparsely cratered satellites are saturated or nearly saturated with impact craters; (ii) these satellites have rotated nonsynchronously over geological time; (iii) most of the craters are made not by heliocentric (Sun-orbiting) comets and asteroids but rather by planetocentric (planet-orbiting) debris of indeterminate origin; or (iv) pathological endogenic resurfacing has created illusions of structure. Callisto's surface is readily classified as nearly saturated. Ganymede's bright terrains, although less heavily cratered than those of Callisto, can also be explained by crater densities approaching saturation on a world where endogenic processes were active. The leading alternative is nonsynchronous rotation, an explanation supported by the distribution of catenae (crater chains produced by impact of tidally disrupted comets). Triton's craters can be explained by planetocentric debris or by capricious resurfacing, but both hypotheses are inherently improbable.

Zahnle, Kevin↗
NASA NTRS1973

Mass property control of a synchronous meteorological satellite scanning experiment.

A scanning mirror assembly which is part of a Synchronous Orbit Meteorological Satellite is an example where mission objectives required measurement and control of weight, mass center, principal moments of inertia, and products of inertia. The scanning mirror oscillates within the spin stabilized spacecraft, and both the scanning motor torque and perturbation of spacecraft attitude and spin rate have to be reduced to low levels. A theoretically ideal solution would be to make the mirror inertia constant about all axes in a plane perpendicular to the oscillation axis. A practically attainable compromise is to locate principal axes preferentially and make the difference between two of them acceptably small. Methods for making the necessary mass property measurements and deriving and applying minimum weight ballast correction to achieve the necessary mass distribution are discussed. It is noted that mass property control operations are typically subject to practical constraints such as geometry and functional operation of the system and capability of available measurement facilities and fixtures.

Lang, W. E.↗
NASA NTRS1969

The use of satellite beacons for meteorological research

The use of microwave beacon transmissions from synchronous and near synchronous satellites is discussed as a means of measuring atmospheric absorption. It is suggested that, with a fixed angle of elevation of a synchronous satellite, complete diurnal coverage of the integrated absorption is available. In addition, with refined interferometric equipment, angle of arrival studies can be made and phase deviations measured.

Aarons, J.↗
NASA NTRS1980

Open-loop nanosecond-synchronization for wideband satellite communications

A synchronization technique for use with an onboard processing satellite communication system is discussed. The satellite oscillator is used both as the system time reference and as the frequency source for all downlink carriers and data clocks. Downlink timing is established at each system earth terminal through a combination of carrier and data-clock tracking and a downlink timing epoch signal consisting of one bit per TDMA data burst. Uplink timing is established by an open-loop range prediction process using precision ephemerides calculated and distributed by the central control station. Overall timing accuracy of the uplink signal at the satellite receiver of + or - 7 nanoseconds permits unambiguous identification of each data bit position in a 128 Mbps TDMA burst. This is accomplished by means of simple, inexpensive terminal hardware using available crystal oscillators for time/frequency references and digital synthesis techniques that may be implemented in digital LSI chips.

Holmes, W. M., Jr.↗
NASA NTRS1983

Orbital and cloud cover sampling analyses for multisatellite earth radiation budget experiments

Computer simulations have been performed to determine the geographical and temporal coverage of various satellite orbits and scanning and nonscanning radiometers for earth radiation budget measurements. These results were used to simulate the sampling of a diurnally varying cloud and radiation field for several different satellite systems to estimate errors in regional monthly mean reflected radiation. The combined results indicate that coincient observations with a minimum of one sun-synchronous satellite and a midinclined orbit satellite are needed to obtain the required regional, zonal, and global coverage with sufficient temporal sampling for obtaining accurate estimates of monthly mean reflected solar radiation. Overall, the best sampling capability and lowest errors were obtained with a three-satellite system, i.e., two sun-synchronous satellites with different equatorial crossing times combined with either a 46 or 57-deg orbit satellite. The results from these analyses have been used in defining a joint NASA-NOAA multisatellite mission for an earth radiation budget experiment.

Harrison, E. F.↗