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Results for “GEODETIC SATELLITE”

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
All sourcesNASA NTRSDOE OSTI
NASA NTRS1968

Intercomparison of GEOS-A observation systems.

NASA geodetic Satellite Observation Systems Intercomparison Investigation, discussing Goddard Range and Range Rate, Laser and MOTS camera systems, AF PC-1000 camera, etc

Berbert, J. H.↗
NASA NTRS1971

The accuracy of laser tracking

A brief discussion of the actual laser tracking performance of geodetic satellites is followed by a discussion of the errors inherent in the laser system. An estimate is made of the capability expected within the next few years for the tracking of a heliocentric probe. The GEOS 1, GRARR, and GEOS 2 systems are considered. Errors in the tracking of a heliocentric probe are noted. These include errors due to the earth's atmosphere, (beam bending, atmospheric absorption, atmospheric turbulence, and atmospheric distortion of short laser pulses), and errors due to coronal effects.

Blamont, J. E.↗
NASA NTRS1972

GEOS-2 C-band radar system project. Marine study using C-band radars

One of the secondary objectives of the GEOS-2 C-band Systems Project is to study the feasibility of using geodetic satellites to both evaluate shipborne instrumentation and to determine ship positions in broad ocean areas. The purpose of this task is to determine whether shipborne C-band radar tracking, in conjunction with ground based tracking, is sufficiently accurate to provide instrumentation evaluation and ship position estimates. Data from several Apollo tracking ships, in particular the USNS Vanguard, was made available for this effort. A series of tests, using the USNS Vanguard, were carried out in the Port Canaveral and Bahama Acoustic Transponder Array Areas. The major portion of the analyses reported are the result of preliminary investigations using the data from these tests.

Source record↗
NASA NTRS1972

Mini-arc orbit determination for the Geos C altimetry experiment.

The problem is, given simultaneous observations of an altimeter-bearing geodetic satellite, from three or more high-precision radar stations, to determine its orbit to submeter accuracy in the presence of perturbations arising from strong, localized gravitational anomalies. A new solution to this problem involves the use of an f and g series specialized to the determination of radial distance (pertinent to the satellite altimeter experiment) to process data over a very short arc (e.g., 6 sec to 10 min). Such a short arc is termed a 'mini-arc.' In this approach, the data batches are connected by dynamics, rather than by the usual curve fit to a power series in time. A nonunity value of the mass factor is introduced to serve as an 'alias' for the perturbations that affect the satellite's path during the mini arc. The essence of the mini-arc approach is to include the influence of the far, or relatively lower-order, force field analytically and to solve for the remaining fine structure with accuracies that can approach a few centimeters.

Baker, R. M. L., Jr.↗
NASA NTRS1975

Project GEOS-C

An oceanographic-geodetic satellite, designated Geodynamics Experimental Ocean Satellite-C (GEOS-C), an earth-orbiting spacecraft designed to measure precisely the topography of the ocean surface and the sea state (wave height, wave period, wave propagation direction) is described. Launch operations, spacecraft description, and mission objectives are included along with a brief flight history of the NASA satellite geodesy program. Principal investigations to be performed by the GEOS-C mission are discussed.

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NASA NTRS1974

A global station coordinate solution based upon camera and laser data - GSFC 1973

The results of a determination of the coordinates of about 70 tracking stations are presented. The data were deived with the aid of dynamical techniques from precise reduced optical and laser observations of geodetic satellites. It is attempted to establish a reasonable accuracy estimate through a comparison of the data with other independent solutions. A brief description is given of the independent solutions used as a source of comparison.

Marsh, J. G.↗
NASA NTRS1978

A picosecond resolution Time Digitizer for laser ranging

The Time Digitizer capable of covering a range of 0.34 sec in 9.76 psec increments is described. The time interval between a pair of start-stop pulses is digitized coarsely in 20 nsec periods by a very accurate 50 MHz reference clock. The residual fractions of a clock period at the start and the stop end of the measured interval are stretched in two interpolators and digitized in 9.76 psec increments. An equivalent digitizing frequency of 102.4 GHz is thus achieved. The digitizer is built in a minicrate and communicates via a standard crate controller. It is intended for use in the laser ranging between ground stations and the Laser Geodetic Satellite (LAGEOS). It is shown that the distribution in any two adjacent 9.76 psec channels of a small number of identical test time intervals is essentially binomial. The performance of the digitizer and test results are given.

Turko, B.↗
NASA NTRS1990

Long-period perturbations in Starlette orbit and tide solution

The long-period perturbations present in the orbit of the Starlette geodetic satellite is analyzed using a one-year continuous orbit from October 1976 through October 1977 and a three-year orbit during 1983 through 1985. A solution for 66 ocean tidal parameters for 14 low-degree tidal constituents is obtained in a simultaneous least squares estimation procedure with other geodynamic and orbit parameters. The yearly values of the second-degree S(a) tides, which have been observed to produce significant seasonal variations on the Starlette node, are included in the solution. Good agreement is found between the solutions, other satellite solutions, the oceanographic tide solutions, and other investigations using the computation of the earth's tidal response. The results indicate that the Starlette tide solutions produces significantly improved orbit fits for both Lageos and Starlette.

Cheng, M. K.↗
NASA NTRS1991

Studies of water storage and other contributions to changes in the rotation of the Earth

The effects were determined of the global redistribution of water mass on various geodetic observables, especially polar motion, and complementary observables such as geodetic satellite positions. The effect of water mass redistribution has been and continues to be less well known and more difficult to observe than effects of air mass distribution, yet the water contribution is potentially significant over a large range of periods. The current understanding is reviewed of the contribution of polar drift, decadal polar motion, Chandler and annual wobbles, and higher frequency polar motion, as determined through the efforts of the funded work within the NASA Crustal Dynamics Project, and in the context of the general literature on the subject. Water mass redistribution is either demonstrably important to the excitation of each of these, or is probably important given a lack of other likely excitation sources.

Wilson, Clark R.↗
NASA NTRS1992

Modeling radiation forces acting on TOPEX/Poseidon for precision orbit determination

Geodetic satellites such as GEOSAT, SPOT, ERS-1, and TOPEX/Poseidon require accurate orbital computations to support the scientific data they collect. Until recently, gravity field mismodeling was the major source of error in precise orbit definition. However, albedo and infrared re-radiation, and spacecraft thermal imbalances produce in combination no more than a 6-cm radial root-mean-square (RMS) error over a 10-day period. This requires the development of nonconservative force models that take the satellite's complex geometry, attitude, and surface properties into account. For TOPEX/Poseidon, a 'box-wing' satellite form was investigated that models the satellite as a combination of flat plates arranged in a box shape with a connected solar array. The nonconservative forces acting on each of the eight surfaces are computed independently, yielding vector accelerations which are summed to compute the total aggregate effect on the satellite center-of-mass. In order to test the validity of this concept, 'micro-models' based on finite element analysis of TOPEX/Poseidon were used to generate acceleration histories in a wide variety of orbit orientations. These profiles are then compared to the box-wing model. The results of these simulations and their implication on the ability to precisely model the TOPEX/Poseidon orbit are discussed.

Marshall, J. A.↗