Thermal deformation measurement of an aluminum alloy telescope model under periodic temperature modulation

The thermal dimensional stability of the telescope is crucial for gravitational wave detection. In many studies, it is evaluated with the telescope placed inside a temperature-controlled chamber, allowing the temperature-deformation coefficient of the sample to be measured under steady-state-like conditions. However, the real thermal condition of the telescope is not a steady thermal condition due to the periodic variation in solar radiation intensity and the intermittent operation of the instruments inside the spacecraft. Furthermore, the thermal deformation outside the gravitational wave detection frequency band (0.1 mHz-1 Hz) will not affect the detection. Therefore, a new, to our knowledge, experimental setup is established in this paper to measure the unsteady thermal deformation of a scaled-down aluminum alloy telescope model under periodic temperature modulation. We find that the temperature-deformation coefficient <i>γ</i>_(<i>f</i>), which represents the ratio of the amplitude of deformation change to the temperature change, of the telescope model is reduced as the temperature modulation frequency increases. Notably, the <i>γ</i>_(<i>f</i>) is much smaller than the coefficient of thermal expansion (CTE) of this material, which means the thermal control requirements derived from the CTE are overly stringent.