Geometrical stability and evolution of the HIPPARCOS telescope
Lindegren, L.; Le Poole, R. S.; Perryman, M. A. C.; Petersen, C.
Sweden, Netherlands, Denmark
Abstract
A simple geometrical model of the Hipparcos telescope is described whereby the relative positions and orientations of critical optical elements can be derived from the field-to-grid transformation determined as part of the normal data processing. The instrument is very stable on time scales of hours, but secular drifts of the order of 0.1 micron/d are observed, and there is evidence for a progressive deformation of the mirrors which may eventually also affect the image quality.