SVOM MXT Instrument: Thermal Control System Design and Verification
Van Haute, Alexandre
Pearson, James F.
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SVOM (Space-based multi-band astronomical Variable Objects Monitor) is a mission developed within a Sino-French cooperation context and dedicated to the detection, localization and study of Gamma Ray Bursts (GRBs) and other high-energy transient phenomena. Four scientific instruments (ECLAIRs and MXT provided by CNES: National French Space Agency, GRM and VT provided by CNSA: China National Space Administration), operating in different wavelengths, constitute the flight segment of the mission. A ground segment (several telescopes and a data center) contributes also to this GRB observations. This paper addresses the MXT instrument, developed by CNES in collaboration with different scientific partnerships (CEA, MPE, IJCLab and the University of Leicester) and dedicated to the observation of GRB afterglows in the soft X-ray band. SVOM is a Low Earth Orbit mission with a specific pointing law thanks to which the spacecraft can quickly change its orientation in order to observe GRB events as soon as they occur. This leads to a very variable and unfavorable external environment for low and stable temperatures. Indeed, the MXT detector (CCD) needs a temperature at -65 °C or lower. Passive cooling cannot achieve such a low temperature. As a consequence, Thermo-Electric Coolers (TEC) insure the additional active cooling. This leads to a significant heat dissipation to be evacuated. A thermal bus with propylene heat-pipes transports this amount of heat from its source to a radiator. Moreover, optical performances (alignment and focus), derived from scientific observations needs, require high performances in terms of temperature stability and uniformity. The paper focuses on the Thermal Control System of the MXT instrument, and more specifically on its design, validation and verification.