Fig. 1. Optical system of the telescope

Fig. 2. Structure schematic diagram of the telescope

Fig. 3. Complete STOP analysis is performed to evaluate the impact of cooling and gravity on the telescope performance

Fig. 4. Optical path of wavefront measurement of the cryogenic telescope

Fig. 5. Testing system

Fig. 6. Calibration of test system

Fig. 7. Calibration results of wavefront error of the collimator

Fig. 8. Process of wavefront measurement of the telescope

Fig. 9. Location layout diagram of temperature measuring points

Fig. 10. Setup of the inside of the chamber

Fig. 11. Setup of the outside of the chamber

Fig. 12. Temperature profiles of the telescope in the course of the experiment

Fig. 13. Changes of the total wavefront figures of the telescope with temperature measured during the cool-down and warm-up processes（λ=0.632 8 μm）

Fig. 14. Changes of the spherical abberration of the telescope with temperature during the cool-down and warn-up processes

Fig. 15. Difference in the wavefront figure of the telescope at a room temperature before and after experiment

Fig. 16. Changes of the zernike coefficient Z10 and Z11 of the wavefront with temperature measured during the cool-down and warn-up processes