Abstract
The optical performance and pointing accuracy of the 1.5 m solar telescope GREGOR depend on the passive and active temperature control design features. Stringent thermal requirements are given in the technical specification for the passive thermal control of telescope structure and the main mirror air cooling system under operational conditions. The telescope structure has to be kept within a range of -0.5K through +0.2K against the ambient temperature. The main mirror temperature has to be kept up to a temperature difference of less than 2K under the ambient temperature with an accuracy of ±0.1K. The temperature difference across the main mirror surface has to be smaller than ±0.1K. Another thermal requirement asks for a main mirror safety cover to prevent the wandering of focused sunlight over the telescope structure in case of control system malfunction or power loss. Features of the chosen passive thermal concept for the telescope structure and the active main mirror air cooling system as well as the primary mirror safety cover system are presented together with the finite element analyses results and tests performed in order to find and verify the chosen design.
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