The GEOS 1 (Geodetic Earth Orbiting Satellite) spacecraft was a gravity-gradient-stabilized, solar-cell powered unit designed exclusively for geodetic studies. It was the first successful active spacecraft of the National Geodetic Satellite Program. Instrumentation included (1) four optical beacons, (2) laser reflectors, (3) a radio range transponder, (4) Doppler beacons, and (5) a range and range rate transponder. These were designed to operate simultaneously to fulfill the objectives of locating observation points (geodetic control stations) in a three dimensional earth center-of-mass coordinate system within 10 m of accuracy, of defining the structure of the earth's irregular gravitational field and refining the locations and magnitudes of the large gravity anomalies, and of comparing results of the various systems onboard the spacecraft to determine the most accurate and reliable system. Acquisition and recording of data were the responsibility of the GSFC Space Tracking and Data Acquisitions Network (STADAN).
A selection of GEOS-1 SLR (satellite laser ranging) data from January 20, 1977 through December 14, 1978 was included in EGM96. This time period spans more than one cycle of the argument of perigee. The satellite was tracked by both SAO and NASA SLR stations.
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