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Flat-top Sun shield is a part of the disturbance reducing system on the space-based gravitational wave detector TianQin. The Sun shield is expected to guards temperature stability of the satellite's top deck from the low-frequency solar flux fluctuation. This paper introduces an analytic method to study the Sun shield's temperature response to sinusoidal variations of incoming heat flux. Oscillation mode of temperature field is described in the form of wave equation, which satisfies globally the thermal diffusion equation. The continuity equation is solved to reveal the wave behaviours when crossing different media. Three typical boundary conditions are studied in order to solve the wave equation. By applying the method to the TianQin's thermal model, the low-frequency temperature response of the Sun shield and the top deck are derived. The results suggest adopting insulation materials with low thermal diffusivity in the thermal design to shield the solar disturbances. [ABSTRACT FROM AUTHOR]

TianQin is a proposed space-borne gravitational wave observatory in high geocentric orbits, exposed to radiating heat sources in space. Due to the stringent thermal stability requirements from the key payloads, the analysis of space thermal environment is of great importance. This paper studies the incident thermal radiation onto the TianQin satellites from the Sun–Earth–Moon system. The solar constant fluctuation (SCF) and the Earth's land-type features, based on the meteorological data, are considered, and an analytic function of lunar surface temperature is used. The analysis includes the solar radiation, the infrared radiation, and the albedo. The results are discussed in both time and frequency domains. The spectral analysis indicates that in the target frequency band of 0.1 mHz–1 Hz, the SCF plays a dominant role, and that the associated incident thermal disturbance is ∼5 W m−2 Hz−1/2 for TianQin, at the same level of the LISA in heliocentric orbits. In addition, the power spectra of the Earth's and Moon's heating fluctuation are given, both order-of-magnitude weaker than that of the solar radiation. The results may contribute to the thermal design and the noise analysis for TianQin. [ABSTRACT FROM AUTHOR]