Calibration data, either covering the entire mission, or per orbit, are presented here to provide further background information on the Hipparcos data. The calibration data reflect the ever changing conditions for the instrument as caused mainly by radiation damage during the four transits each day through the Van Allen radiation belts. Consequences varied from darkening of the optics for the image dissector tube (part of the main field detector chain) to the final breakdown of the gyroscopes ad the on-board computer.
With Hipparcos left in a geostationary transfer orbit of about 11 hours, and no data gathering possible near perigee, the calibrations naturally subdivided into orbits. The counting of those orbits started with the first observations on 5 November 1989. Where relevant, the calibration data will show the orbit number for the data at the cursor position, as well as the time in years since 1989.0.
This section presents the results for a small number of calibrations that can be of interest in the interpretation of the data. It is accessed through a tab on the main window, and provides links to calibrations that are to do with
- the focal plane assembly
- astrometric calibrations
- star mapper calibrations
- miscellaneous calibrations
The calibration data have a limited pop-up menu, with
- increase dot
- decrease dot
- align charts
- pdf copy
- toggle colour legend
- toggle legend
The last two options are activated depending on the properties of the chart shown. Calibrations are often related to satellite orbits, and orbit numbers are part of the interactive display.