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TOPEX/Poseidon: Perspectives on an Ocean Planet

- High Gain Antenna

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hga

The high gain antenna is part of the primary communication link between the spacecraft and the TDRSS satellites, which in turn communicate with ground stations. Mission operators use this link to download the science and engineering information in TOPEX/Poseidon's tape recorders, as well as to command, monitor, and track the satellite.

During launch, the high gain antenna was stowed along the side of the spacecraft, and was not operable. It remained in this position until 22 hours after launch. During these 22 hours, all spacecraft communication took place through the zenith and nadir omni antennas.

The high gain antenna is a 1.3 meter parabolic dish antenna mounted on a 2.6 meter boom on the zenith side of the spacecraft. Between the end of the boom and the dish are two gimbal joints mounted perpendicular to each other which allow the antenna to be pointed in any direction above or to the side of the spacecraft. This flexibility allows TOPEX/Poseidon to locate and establish communication with any one of the TDRSS satellites which happens to be in the satellite's zenith hemisphere.