Thermal control of a spacecraft: Backward-implicit scheme programming and coating materials analysis

Abstract

[EN] The passive thermal control of a satellite consists of establishing the necessary thermal parameters involved in the process of heat transfer by radiation and conduction in order to delimit the range of temperatures to which the different components will be exposed. If the obtained range implies temperatures that the elements of the satellite are unable to cope with, therefore, an external control is demanded. This work deals with the programming of the equilibrium thermal problem taken into consideration a backward-implicit scheme. The algebraic mathematical approach for steady-state and transient analysis are implemented in Matlab scripts. In addition, the work analyzes the influence of different coating materials on the passive thermal control of a benchmark spacecraft reported in the literature. The problem under scope considers the characteristics of a low Earth Orbit: the solar, albedo and planetary radiation, the radiation coming from other isotherm surfaces of the same satellite, the heat conduction and, finally, the radiation of these isotherm surfaces to the outer space. The procedure implemented is based on a feasible matrix formulation and results avoid the numerical instabilities prevalent in the forward-explicit approach, moreover, it enables further parametric and sensitivity analysis. Regarding the coating materials influence on the thermal response, the most relevant results evidence that thermal surfaces can guarantee the desirable range of temperature in a spacecraft. We confirm that certain material properties like the absorptance, emittance and its relation (absorption coefficient) are essential in the thermal response of the system. Nevertheless, these thermal properties do not influence in the same way. It is shown that the effect of the emittance is lower than the absorptance.