Thermal characteristics analysis of an optical window in a space telescope

Thermal characteristics are significant parameters for the thermal design of the optical window, which is an important part of the imaging spectrograph of the space telescope. They have a great impact on the temperature of optical window lenses and other optical elements such as the primary mirror, whose temperature is affected by the transmitted energy. For the optical window composed of multiple lenses, it is difficult to obtain thermal characteristics of each lens in the actually reaching solar spectral range through measurement, which causes difficulty in obtaining the accurate predicted temperature of the optical window and evaluating the thermal effect of transmitted energy on the telescope through simulation analysis. In this paper, taking the optical window of the Hα imaging spectrometer of the Chinese Hα solar explorer as an object of study, we propose, to our knowledge, a new concept to calculate the relationship between the thermal characteristics of the optical window and its band-pass filter design. By analyzing the distribution of incident solar spectral energy, the equivalent thermal characteristics of the lenses are calculated. On this basis, thermal analysis and experimental study of the optical window are carried out. The maximum absolute difference is 1.5°C between thermal analysis and on-orbit data, which verifies the consistency of energy distribution simulated with equivalent parameters and the actual situation, proving the effectiveness of this new concept. The concept solves the difficulty in simultaneous calculation of the thermal effect of multiple factors in the space environment, including on-orbit varying external heat flux and complex solar spectral energy distribution caused by the band-pass filter, which is significant in the thermal analysis of the optical window of the space telescope.