Encyclopedia Astronautica
1965.11.06 - Explorer 29


The primary objective of GEOS-A was to provide global geodetic measurements for determining the positions of fiducial control points on the Earth to an accuracy of 10 meters in an Earth centre of mass co-ordinate system, and to determine the structure of the Earth's gravity field to 5 parts in 10 million. 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 fulfil the objectives of locating observation points (geodetic control stations) in a three dimensional earth centre-of-mass co-ordinate 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. In January 1967, a failure in the satellite's command system rendered several geodetic systems inoperable. Radio doppler measurements and the passive laser reflector experiment could continue indefinitely, however.

Acquisition and recording of data were the responsibility of the GSFC Space Tracking and Data Acquisitions Network (STADAN). Ten major observing networks were used. Primary power for the instrumentation was obtained from solar cells that covered most of the exterior of the satellite. The program was directed by NASA’s Goddard Space Flight Center. Prime Contractor was The Johns Hopkins University Applied Physics Laboratory.

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