Thermal Tolerances

Abstract

The fundamental information that the designer, construction engineer and telescope operator wants from the preceding chapters are thermal tolerance criteria on which to build a telescope and that can be used to evaluate the thermal performance of an operating telescope. The thermal tolerance criteria derived in this chapter are based on beam pattern calculations explained in Chap. 12, which indicate that a good telescope performance is obtained if the deformations of the beam forming wavefront do not exceed ~1/16 of the wavelength of observation λ, if the focus is stable within ~λ/10 and if the pointing is stable within ~1/10 of the beam width. Interferometer telescopes should have, in addition, a path length stability of ~λ/10 or better. These performance criteria should be fulfilled during a considerable length of time before a calibration of the telescope needs to be made. The performance criteria translate into mechanical tolerances and these into thermal tolerances of the telescope structure.