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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 307 records · Page 17
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NASA NTRS1977

IMS/Satellite Situation Center report. Daily summary for IMS high-altitude satellites, days 182-365 1977

The orbital positions of a number of high-altitude satellites, capable of making magnetospheric measurements in the second half of 1977, are described. The following satellites are considered: Vela 5A, Vela 5B, Vela 6A, Vela 6B, Solrad 11A, Solrad 11B, Hawkeye 1, Prognoz 5, Explorer 47, Explorer 50, and ISEE-A/-B. The orbit elements used for generating the satellite ephemeris are shown. Complete presentations of the positions of these satellites for the second half of 1977 are given, as well as the IMS/SSC special periods. Detailed plots illustrating these periods are provided. Time-ordered tables of magnetopause crossings, bow shock crossings, neutral sheet passes, midlatitude magnetotail passes, high-latitude magnetotail passes, and Hawkeye 1 northern cusp passes are presented. Bar charts covering the second half of 1977 are given which identify thirteen special periods (Nos. 10-22) based upon certain conjunctions of the high-altitude satellites.

Source record↗
NASA NTRS1975

Earth resources technology system standalone software package: Description and user's guide

A user's guide and program description for the ERTS-B Stand-Alone Software Package is presented. This package was developed to compute the Keplerian elements at the descending node, the Brouwer mean elements at the node, the averaged Brouwer Mean Elements, and other orbital parameters for the orbits of the Earth Resources Technology Satellite (ERTS). The typical input for the program is an ephemeris file which resulted from a definitive orbit generated over a two day arc using the Cowell option in the Definitive Orbit Determination System (DODS) or the Goddard Trajectory Determination System (GTDS).

Chu, W. W.↗
NASA NTRS1976

The Lageos satellite

The fundamental concept of Lageos is a long-lived, dense, electrically and mechanically inert spherical satellite with its surface speckled with retroreflecting cube corners, designed such that range measurements between duly equipped laser ground stations and the satellite are possible with an ultimate accuracy of 2 cm when data from a single satellite pass are appropriately averaged. The Lageos concept requires that the satellite be placed in an orbit for which an ephemeris can be determined ultimately to 5 cm rms uncertainty for a 24-hour arc. These required satellite characteristics should allow the several geodynamic motions experienced by ground stations to be determined typically with 2 cm accuracy.

Johnson, C. W.↗
NASA NTRS1977

de Sitter's theory flattens Jupiter

The discrepancy between values of Jupiter's dynamic oblateness as measured by space probes and via 1971 beta Sco occultations is re-examined. The indicated correction to the Io ephemeris is compared to corrections proposed by Aksnes and Franklin (1975, 1976). It is found that the latter corrections reduce the above discrepancy to a marginal level.

Hubbard, W. B.↗
NASA NTRS1977

Three-dimensional determination of the center of the Watts datum relative to the lunar center of mass

The location of the origin of the Watts datum for the marginal zone of the moon is determined using results of 2770 photoelectric occultation observations obtained over an 18-yr period in combination with 1787 laser time-delay measurements carried out over a five-year period. The lunar ephemeris employed is an experimental one developed from a much shorter span of laser observations. The final solution is obtained by adopting LURE2 parameters and correcting 19 lunar orbital, solar orbital, and coordinate-system parameters. The offsets for the center of the Watts datum are found to be approximately +6.8 km for x1, -2.5 km for x2, and +0.06 km for x3 with respect to the lunar principal axes of inertia.

Mulholland, J. D.↗
NASA NTRS1977

The sun-tracking control of solar collectors using high-performance step motors

Sun-tracking solar energy-focusing devices involving a central receiver, thermionic conversion, or a distributed solar thermal collector system are described. The Perkins solar collector uses a fixed focal point about which an 18 m-diameter parabolic dish moves on tracks. The elevation axis also moves on a circular track. A microprocessor manipulates sun sensor information and sun ephemeris data to ensure correct placement. Stepper motors are digital devices which provide direct interface with digital electronics and a wide dynamic range, and could easily be associated with the microprocessors. Design philosophy, performance criteria, wind load analysis, and control system requirements are also discussed.

Hughes, R. O.↗
NASA NTRS1977

Properties of satellite orbits - Ephemerides, dynamical constants, and satellite phenomena

A short account is given of the history of the observation of the Galilean satellites, with an emphasis on early orbital work and practical applications thereof to world mapping and navigation. The general character of satellite motion is described from a geometric and physical point of view without reference to mathematics. This is followed by a similar discussion of ordinary and mutual satellite phenomena. The accuracies of published ephemerides are discussed on the basis of the observations and theories available for the various satellites. The ephemeris tables need to be revised and, perhaps, partly replaced by well-documented computer programs. The determination of physical parameters (planetary masses and oblatenesses; masses, sizes, and albedo maps of satellites) from positional observations of satellites and photometric observations of ordinary and mutual satellite phenomena is discussed.

Aksnes, K.↗
NASA NTRS1977

Data processing for the DMSP microwave radiometer system

A software program was developed and tested to process microwave radiometry data to be acquired by the microwave sensor (SSM/T) on the Defense Meteorological Satellite Program spacecraft. The SSM/T 7-channel microwave radiometer and systems data will be data-linked to Air Force Global Weather Central (AFGWC) where they will be merged with ephemeris data prior to product processing for use in the AFGWC upper air data base (UADB). The overall system utilizes an integrated design to provide atmospheric temperature soundings for global applications. The fully automated processing at AFGWC was accomplished by four related computer processor programs to produce compatible UADB soundings, evaluate system performance, and update the a priori developed inversion matrices. Tests with simulated data produced results significantly better than climatology.

Rigone, J. L.↗
NASA NTRS1977

Viking Imaging of Phobos and Deimos: An Overview of the Primary Mission

During the Viking primary mission the cameras on the two orbiters acquired about 50 pictures of the two Martian moons. The Viking images of the satellites have a higher surface resolution than those obtained by Mariner 9. The typical surface resolution achieved was 100-200 m, although detail as small as 40 m was imaged on Phobos during a particularly close passage. Attention is given to color sequences obtained for each satellite, aspects of phase angle coverage, and pictures for ephemeris improvement.

Duxbury, T. C.↗
NASA NTRS1977

ALSEP-quasar differential VLBI

A program of ALSEP-quasar very-long-baseline interferometry (VLBI) is being carried out. These observations employ primarily a 'four-antenna' technique whereby simultaneous observations with two antennas at each end of an intercontinental baseline are used to derive the differential interferometric phase between a compact extragalactic radio source (usually a quasar) and a number of ALSEP transmitters on the lunar surface. A continuous ALSEP-quasar differential phase history over a period of a few hours will lead to milliarcsecond angular accuracy in measuring the lunar position against the quasar reference frame if suitable calibration measurements are obtained. Development of this application of the four-antenna technique has been underway for more than a year and is producing high-quality data utilizing Deep Space Network stations. These high-accuracy observations are of value to tie the lunar ephemeris to a nearly inertial extragalactic reference frame, to test gravitational theories, and to measure the earth-moon tidal friction interaction.

Slade, M. A.↗
NASA NTRS1977

Autonomous satellite navigation with the Global Positioning System

This paper discusses the potential of using the Global Positioning System (GPS) to provide autonomous navigation capability to NASA satellites in the 1980 era. Some of the driving forces motivating autonomous navigation are presented. These include such factors as advances in attitude control systems, onboard science annotation, and onboard gridding of imaging data. Simulation results which demonstrate baseline orbit determination accuracies using GPS data on Seasat, Landsat-D, and the Solar Maximum Mission are presented. Emphasis is placed on identifying error sources such as GPS time, GPS ephemeris, user timing biases, and user orbit dynamics, and in a parametric sense on evaluating their contribution to the orbit determination accuracies.

A J Fuchs↗
NASA NTRS1978

Galilean satellites - Analysis of photometric eclipses

The excellent series of photometric eclipses of the Galilean satellites observed at Harvard from 1878 to 1903, which formed the basis for Sampson's study of the Galilean satellites, have been combined with the relatively few available post-1903 photometric eclipse observations in order to evaluate the satellite parameters which occur in the new theory of motion of the satellites. After obtaining values for the epsilon-beta parameters, the mutual eclipses and occultations observed in 1973 are compared with the new theory in order to assess the degradation which might occur in the 84 years which have elapsed since the mean epoch of the photometric eclipses. The results indicate that the new theory satisfactorily can predict ephemeris positions of the Galilean satellites over spans of nearly a century and that it will be a useful tool for analyzing future observations.

Lieske, J. H.↗
NASA NTRS1978

The experimental oceanographic satellite Seasat-A

The experimental Seasat-A satellite, scheduled for launch in 1978, is designed to provide measurements of sea-surface temperature, surface wind speed and direction, sea state and directional wave spectra. The instrument package of the satellite includes a highly precise radar altimeter, a wind-field scatterometer, a synthetic-aperture imaging radar, a scanning multifrequency microwave radiometer and a radiometer operating in the visual and infrared. Tides, currents and storm surges on the marine geoid may be monitored through analysis of range information from the radar altimeter and a satellite ephemeris; sea-ice reconnaissance is also planned.

Dunne, J. A.↗
NASA NTRS1978

Investigations of Mars dynamics and geodesy via the Viking spacecraft

Results are reported for analyses of Doppler, ranging, and tracking data from the Viking landers and orbiters of relevance to the dynamics and geodesy of Mars. Highly improved numerical results are given for the orientation of the spin axis of Mars, the planet's sidereal rotation rate, and the earth-Mars ephemeris. A refined definition of the global gravitational field of Mars is discussed, a local gravitational survey based on Viking Orbiter 2 tracking data is described, and a mass anomaly near Olympus Mons is noted. Radius data are examined which suggest an asymmetry in the figure of Mars characterized by generally higher topography in the southern than in the northern hemisphere. The mass of Phobos is determined on the basis of Orbiter 1 orbital perturbations, and the mean density of this Martian satellite is found to be approximately 2.0 g/cu cm, which is suggestive of primitive carbonaceous chondrites and, if true, implies that Phobos was formed in the asteroid belt.

Michael, W. H., Jr.↗
NASA NTRS1978

Earth viewing with a shuttleborne experiment pointing mount

The article considers the attitude determination and the control problems of the shuttleborne earth-viewing pointing mounts (EPMs). Per-axis pointing performance requirements are identified for troposphere/stratosphere pollution, tropical storm research, and urban air pollution. Ephemeris error contributions to earth pointing are discussed and candidate attitude reference systems are described. Primary interfaces between the orbiter flight control system, Spacelab, pallet-mounted EPM, and control subsystems are outlined. A block diagram is given of the EPM-mounted stellar-inertial attitude reference system. The system's performance is evaluated on the basis of the inertial sensor and a three-axis covariance analysis.

Iwens, R. P.↗
NASA NTRS1979

Goddard trajectory determination

Goddard Trajectory Determination System (GTDS), programs designed to support Earth, lunar and interplanetary missions are used as research and development tool. Program displays research and development used in trajectory determination, preflight and postflight analyses, simulation of tracking data, ephemeris generation, and related tasks.

Dixon, B.↗
NASA NTRS1978

Compression of ephemerides by discrete Chebyshev approximations

The use of Chebyshev series in representing the ephemerides of satellites and planets in terms of truncated polynomial series is discussed. Emphasis is placed on a FORTRAN package which was developed for fitting satellite orbits. The features desired in any approximation are: (1) the ability to compress a satellite emphemeris; (2) the ability to represent a satellite ephemeris over several orbits; (3) guaranteed accuracy to within prescribed tolerance over the time interval of consideration; and (4) fast processing. These features are imposed with an eye towards adapting the approximation for use on microprocessor applications in which storage is limited and real time processing is required.

Pickard, H. M.↗
NASA NTRS1978

ISEE-C attitude determination using fine sun sensor data only

Techniques developed to determine the spin axis attitude using Fine Sun Sensor (FSS) data only are described. At any given time, the Sun angle specifies the orientation of the spin axis relative to the sunline. The instantaneous time rate of change of the sun angle is directly proportional to the orientation of the spin axis relative to a reference plane that is normal to the ecliptic. Thus, the spin axis attitude can be determined when sufficient data has been collected to accurately measure the rate of change of the sun angle. The uncertainties can be computed directly from the uncertainties in the coefficients of the smoothed sun angle curve. The FSS-only technique is unique in that ephemeris vectors are required only to transform the attitude results to more conventional coordinate frames. The combination of the mission geometry and the FSS accuracy make ISEE-C an ideal mission for applying this method. However, the technique can be used on other missions, such as spin stabilized geosynchronous missions.

Gunshol, L. P.↗