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At least 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Future development of IR thermovision weather satellite equipment

The self radiation of the surface being viewed is used for image synthesis in IR thermovision equipment. The installation of such equipment aboard weather satellites makes it possible to obtain cloud cover pictures of the earth's surface in a complete orbit, regardless of the illumination conditions, and also provides quantitative information on the underlying surface temperature and cloud top height. Such equipment is used successfully aboard the Soviet satellites of the Meteor system, and experimentally on the American satellites of the Nimbus series. With regard to surface resolution, the present-day IR weather satellite equipment is inferior to the television equipment. This is due primarily to the comparatively low detectivity of the IR detectors used. While IR equipment has several fundamental advantages in comparison with the conventional television equipment, the problem arises of determining the possibility for future development of weather satellite IR thermovision equipment. Criteria are examined for evaluating the quality of IR.

Listratov, A. V.↗
NASA NTRS1975

Drag coefficients for astronomical observatory satellites

The first experimental European communications satellite Symphonie is a geostationary satellite. The satellite is designed and built in a joint project by French and German aerospace firms. A description is given of the basic technical concept of the satellite. The apogee motor is discussed along with the satellite stabilization system. The stabilization system provides a three-axis positional stabilization and an orbital stabilization. Attention is given to the spin stabilization phase, the sensors employed, the approache used for orbital correction maneuvers, and the conduction of simulation tests on the ground.

Williams, R. R.↗
NASA NTRS1975

A co-accretional model of satellite formation

A model of the accumulation process of a satellite about an accreting planet is proposed in order to explain the difference in relative size between the moon and the outer planets' satellites. The parameter that most strongly affects the final mass ratio of the pair in this model is the time at which the secondary embryo is introduced. Thus the difference between terrestrial and outer planet satellite systems is easily understood in terms of the differences in Q (the specific dissipation function of the particles in the circumplanetary cloud) between these planets. The high Q of the outer planets does not allow a satellite embryo to survive a significant portion of the accretion process; therefore only small bodies formed very late in the accumulation of the planet remain as satellites.

Harris, A. W.↗
NASA NTRS1975

An operational application of satellite snow cover observations, northwest United States

LANDSAT-1 imagery showing extent of snow cover was collected and is examined for the 1973 and 1974 snowmelt seasons for three Columbia River Basins. Snowlines were mapped and the aerial snow cover was determined using satellite data. Satellite snow mapping products were compared products from conventional information sources (computer programming and aerial photography was used). Available satellite data were successfully analyzed by radiance thresholding to determine snowlines and the attendant snow-covered area. Basin outline masks, contour elevation masks, and grid overlays were utilized as satellite data interpretation aids. Verification of the LANDSAT-1 data was generally good although there were exceptions. A major problem was lack of adequate cloud-free satellite imagery of high resolution and determining snowlines in forested areas.

Dillard, J. P.↗
NASA NTRS1975

Jupiter orbiter lifetime: The hazard of Galilean satellite collision

The four Galilean satellites of Jupiter present a long-term collision hazard to an uncontrolled orbiting spacecraft that repeatedly enters the spatial region occupied by the satellites. Satellite close encounters and the likelihood of collision over a wide range of initial orbit conditions were analyzed. The effect of orbit inclination was of key interest. The scope of the analysis was restricted to orbital dynamic considerations alone, i.e. the question of biological contamination given the event of collision was not considered. A quarantine or orbiter lifetime of 50 years was assumed. This time period begins at spacecraft shutdown following completion of the mission objectives. A numerical approach was adopted wherein each initial orbit is propagated for 50 years, and satellite closest encounter distances recorded on every revolution. The computer program includes approximations of the three major perturbation effects on the long-term motion of the orbiter: (1) Jupiter oblateness, (2) solar gravity, and (3) satellite gravity.

Friedlander, A. L.↗
NASA NTRS1976

Mesoscale temperature and moisture fields from satellite infrared soundings

The combined use of radiosonde and satellite infrared soundings can provide mesoscale temperature and moisture fields at the time of satellite coverage. Radiance data from the vertical temperature profile radiometer on NOAA polar-orbiting satellites can be used along with a radiosonde sounding as an initial guess in an iterative retrieval algorithm. The mesoscale temperature and moisture fields at local 9 - 10 a.m., which are produced by retrieving temperature profiles at each scan spot for the BTPR (every 70 km), can be used for analysis or as a forecasting tool for subsequent weather events during the day. The advantage of better horizontal resolution of satellite soundings can be coupled with the radiosonde temperature and moisture profile both as a best initial guess profile and as a means of eliminating problems due to the limited vertical resolution of satellite soundings.

Hillger, D. W.↗
NASA NTRS1975

Availability of a communications satellite - Requirement and feasibility

An estimated 45 communications satellites will be in geostationary orbit in the 1980s. Based on past history, half of the subsystem failures will be due to design failures. Methods now used to achieve present availabilities are summarized in this paper. To increase the availability of a single satellite to 99.99%, new techniques are needed; several possibilities are suggested herein. New developments, including nickel-hydrogen batteries, magnetic bearings, and solid-state amplifiers, are possible solutions to long standing problem areas in communications satellites. Launching a satellite two or three years before the system is needed is one way to reduce design failures in subsequent satellites. Diversity of manufacture can be used to obtain the maximum advantage from redundant elements. Finally, unmanned module exchange at geostationary orbit has been shown to be technically feasible.

Gordon, G. D.↗
NASA NTRS1975

Minimum thrust levels for spinning drag-free satellites

A drag-free satellite, which contains an internal unsupported proof mass, is shielded from external forces such as solar pressure. Thrustors force the satellite to follow the proof mass and hence the satellite follows an almost purely gravitational orbit. The dominant internal disturbing force is the mass attraction of the satellite on the proof mass. Spinning the satellite reduces this force and it has been investigated what the size of the thrustors must be in this case. This size is much smaller than originally thought. Its impact on some other features is shown.

Olsder, G. J.↗
NASA NTRS1976

Heavy ions from the Galilean satellites and the centrifugal distortion of the Jovian magnetosphere

The Galilean satellites constitute a potentially significant source of plasma to the Jovian atmosphere. The paper examines the distortion of the Jovian magnetosphere that would result from injection of ions at the Galilean satellites. The magnetic distortion produced is a localized perturbation near the equatorial plane, in contrast to the large-scale distortion produced by Jovian atmospheric ions. The study estimates the relative perturbation currents resulting from the two sources in terms of the unknown ion production rate at the satellites. It is found that the two perturbations would be of comparable magnitudes if the ion source flux at all of the Galilean satellites were comparable to the photo-ion escape flux from Jupiter's atmosphere. More specifically, ions produced by the Galilean satellites should be confined near the equatorial plane of Jupiter's magnetosphere in a sheet whose thickness is determined by a centrifugal scale height given essentially by the ion thermal speed divided by the corotation frequency.

Hill, T. W.↗
NASA NTRS1976

Planning for a data base system to support satellite conceptual design

The conceptual design of an automated satellite design data base system is presented. The satellite catalog in the system includes data for all earth orbital satellites funded to the hardware stage for launch between 1970 and 1980, and provides a concise compilation of satellite capabilities and design parameters. The cost of satellite subsystems and components will be added to the base. Data elements are listed and discussed. Sensor and science and applications opportunities catalogs will be included in the data system. Capabilities of the BASIS storage, retrieval, and analysis system are used in the system design.

Claydon, C. R.↗
NASA NTRS1976

An analysis of satellite state vector observability using SST tracking data

Observability of satellite state vectors, using only SST tracking data was investigated by covariance analysis under a variety of satellite and station configurations. These results indicate very precarious observability in most short arc cases. The consequences of this are large variances on many state components, such as the downrange component of the relay satellite position. To illustrate the impact of observability problems, an example is given of two distinct satellite orbit pairs generating essentially the same data arc. The physical bases for unobservability are outlined and related to proposed TDRSS configurations. Results are relevant to any mission depending upon TDRSS to determine satellite state. The required mathematical analysis and the software used is described.

Englar, T. S., Jr.↗
NASA NTRS1977

The status of environmental satellites and availability of their data products

The latest available information about the status of unclassified environmental satellite (flown by the United States) and their data products is presented. The type of environmental satellites discussed include unmanned earth resource and meteorological satellites, and manned satellites which can act as a combination platform for instruments. The capabilities and data products of projected satellites are discussed along with those of currently operating systems.

Hughes, C. L.↗
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 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 NTRS1976

Jupiter: Studies of the interior, atmosphere, magnetosphere and satellites; Proceedings of the Colloquium, Tucson, Ariz., May 19-21, 1975

This volume is a comprehensive technical text covering all scientific aspects of Jupiter's interior, atmosphere, magnetosphere, and satellites. The chapters deal with such general subjects as the origin and interior structure of Jupiter, the planet's atmosphere and ionosphere, as well as its magnetosphere, radiation belts, and satellites. Specific topics include a review of theories on the origin and structure of Jupiter and its satellites, interior models of Jupiter, the planet's gravity field, its thermal and atmospheric structure, model ionospheres, chemistry and spectroscopy of the atmosphere, the IR spectrum of the planet, and the meteorology of the atmosphere. Other chapters discuss radio observations of Jupiter, the dynamics of the Jovian magnetosphere, structural and thermal models of the icy Galilean satellites and Io's atmosphere and optical emissions. Results are evaluated for the IR radiometer experiment on Pioneers 10 and 11, radio occultation measurements from the Pioneer probes, Pioneer 10 UV photometric observations of the planet and its satellites, Pioneer 10 and 11 imaging polarimetry, the plasma analyzer experiment on the two probes, and observations of energetic Jovian electrons and protons. Individual items are announced in this issue.

Gehrels, T.↗
NASA NTRS1976

The motions of satellites and asteroids - Natural probes of Jovian gravity

Before the recent Pioneer probes, our knowledge of Jupiter's gravitational field was obtained from the motions of satellites and asteroids. The study of orbital perturbations of asteroids near the 2:1 commensurability yielded a value of the mass of the Jupiter system at least as precise as that obtained by the artificial probes. Precession of the inner satellites' orbits placed constraints on the harmonic coefficients J2 and J4. A correction to the satellite determination of J4 lowers its mean value closer to the Pioneer result. The orbital grouping among the outer satellites and the resonance among the Galilean satellites are described in detail, but the origins of these phenomena are not understood. However, recent research suggests that the explanation will be intimately associated with models of the origin and evolution of the planet itself.

Greenberg, R. J.↗
NASA NTRS1977

Improvement in the geopotential derived from satellite and surface data /Gem 7 and 8/

A refinement has been obtained in the earth's gravitational field by using satellite and surface data. In addition to a more complete treatment of data previously employed on 27 satellites, the new satellite solution Gem 7 (Goddard Earth Model 7) includes 64,000 laser measurements taken on seven satellites. Gem 7, containing 400 harmonic terms, is complete through degree and order 16. The companion solution Gem 8 combines the same satellite data as Gem 7 with surface gravimetry over 39% of the earth. Gem 8 is complete to degree and order 25. Extensive tests on data independent of the solution show that the undulations of the geoidal surface computed by Gem 7 have an accuracy of about 2.5 m (rms). The overall accuracy of the geoid calculated by Gem 8 is estimated to be about 4 m (rms). The new combination solution is the first to show signs of 'convection rolls' in the upper mantle below the Pacific Ocean.

Wagner, C. A.↗
NASA NTRS1977

Rotation histories of the natural satellites

Recent advances in the theory of rotation are combined with traditional approaches to study the rotational evolution of the 33 known natural satellites. A calculation similar to that reported by Burns and Safronov (1973) is applied to each satellite to obtain the characteristic time of decay of any wobble motion to smooth rotation about the principal axis of maximum moment of inertia. Stability criteria and capture probabilities are calculated for the 3/2 spin resonance. Results show that only the regular satellites and Iapetus, Hyperion, Triton, and the moon are tidally evolved. Of these, 13 have confirmed synchronous rotation periods; capture probabilities into the 3/2 resonance indicate that none of the remaining 10 should be captured in nonsynchronous, commensurate spin states. For the most part, the irregular satellites retain their original spins except for a relaxation to principal axis rotation. Tidal evolution of the obliquities of the satellites is evaluated in the framework of the generalization of Cassini's laws for the moon. Nearly resonant, forced librations in longitude of 4.8 and 0.5 deg are calculated on the basis of the observed shapes of Phobos and Deimos, respectively.

Peale, S. J.↗