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Spacecraft-Parameter Calibrations

Part of the Astrophysics and Space Science Library book series (ASSL, volume 350)

All on-board measurements were regulated by signals derived from the on-board clock. The stability of these timings can be checked by comparing the on-board times with the ground-station times. Hipparcos had very limited memory for on-board data storage, and its operations depended on continuous contact with a ground station for immediate downloading of observations. The telemetry was sent to the ground station in telemetry formats, covering 10.667 s of operations (spacecraft and payload). Each format received by the ground station, was time-tagged using a signal from the ground-station clock. With the orbital position of the satellite generally known to within a few hundred meter, the time delay between satellite and ground station could be calculated to the sub-micro second level, thus providing a direct comparison between on-board and ground-station clocks. For obvious reasons, the groundstation clock was considerably more stable than the on-board clock, and drifts between the two could generally be assigned to the on-board clock. What was not always stable, however, was the ground-station time delay: the time passed between the signal reaching the antenna and it being time-tagged. This applied in particular to the Goldstone ground station.

Keywords

Spin Axis Attitude Control System Heat Intake Clock Drift Reduction Figure 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer Science + Business Media B.V 2008

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