Verification of the HIPPARCOS payload short term stability performances.

The stringency of the short term stability requirements stipulated for the Hipparcos payload have led to great efforts to verify the pertinent performance parameters through a complex combination of analyses and testing. Attention is presently given to the development of test apparatus and methodologies capable of yielding accuracies in the nanometric displacement range and the tenth-of-arcsec rotation range. The performance parameters in question encompass the thermoelastic deformation of mirrors and the apparent position of the grid perpendicular to the scan axis, with respect to the basic angle, and image grid rotation and defocus, with respect to distortion.