Behaviour of Thermal Control Coatings Under Atomic Oxygen and Ultraviolet Radiation

Abstract

The Thermal Control Department of CNES (French Space Agency) Toulouse Space Centre has developed many materials and thermal control coatings for satellites and launchers. Some of them have been specially developed to be used in low Earth orbit (LEO). These coatings are resistant to the conditions encountered at this orbit: vacuum, atomic oxygen, thermal cycling, and ultraviolet radiation.These coatings are: electrically conductive or non-conductive black and white paints; protective coating (MAPATOX K) for organic materials which are sensitive to atomic oxygen; new high performance low cost cold coatings named flexible solar reflectors (FSR) which could replace the second surface mirrors (SSM) in LEO.In this paper we present the results of the behaviour of these thermal control coatings under simulated LEO environment. Firstly, we describe the behaviour of black and white silicone and polyurethane paints under atomic oxygen (AO), and secondly, the behaviour of the new white silicone paints, of the MAPATOX K and of the FSR under AO and ultraviolet (UV) combined exposure.In the first part, it has been shown that the polyurethane paints are not stable towards AO but the silicone paints are stable. The new white silicone paints, SG121 FD (electrically non-conductive) and PCBE (electrically conductive) developed to replace SG120 FD and PCBZ, have a good stability towards AO. The new polysiloxane coating named MAPATOX K is a good solution to protect Kapton against AO, The new polysiloxane coating named FSR could replace the SSM for LEO applications.In the second part, the AO and UV combined effect is studied on the new CNES developed thermal control coatings: SG121 FD, PCBE, FSR and MAPATOXK. It has been shown that SG121 FD, PCBE and FSR are more sensitive to AO than to UV, MAPATOX K is not sensitive to AO and UV. The maximal degradation of the solar absorption factor is associated with the AO bombardment prior to UV irradiation.