Spacecraft cavity venting and outgassing analysis applied to the SMILE mission

Abstract

As the instruments of satellites are getting more sophisticated, they are also getting more sensitive to external influences. Deposition of gases due to the low-temperature environment can be one of these external influences. For the European-Chinese SMILE mission, a Soft X-Ray Imager (SXI) is present which has CCD’s exposed to very low temperature. As water vapour is present in the air, as well as water absorbed into the paint of the enclosure, ice deposition could happen under specific conditions. To assess the outgassing of PU1 paint, an experimental outgassing study has been performed at room temperature. Additionally, numerical simulations are performed both in the continuum and the molecular regime to assess the proper functioning of the venting paths. A semi-theoretical correlation is provided which allows calculating the mass flow leaving the instrument based on the internal pressure and temperature. For the specific application of the SXI instrument, the venting rate of the enclosed air is assessed. Also, the outgassing of water vapour should not result in pressure conditions which could trigger ice deposition on the cold CCD surface. Based on the performed simulations and experiments, no issues are expected for the SXI.