Thermal study of payload module for the next-generation infrared space telescope SPICA in risk mitigation phase

• The 3.2 m infrared telescope has to be cooled lower than 6 K in SPICA.
• 13 Working items were established in order to mitigate 5 high risks in RMP.
• The use of truss separation mechanism has been determined to reduce the heat load.
• The baseline of mechanical cooler system has been determined.
• Analytical heat load for 4.5 K stage has been lower than 30 mW with 25

SPace Infrared telescope for Cosmology and Astrophysics (SPICA) is a pre-project of JAXA in collaboration with ESA to be launched around 2020. The SPICA is transferred into a halo orbit around the second Lagrangian point (L2) in the Sun–Earth system, which enables us to use effective radiant cooling in combination with mechanical cooling system in order to cool a 3 m large IR telescope below 6 K. At a present, a conceptional study of SPICA is underway to assess and mitigate mission’s risks; the thermal study for the risk mitigation sets a goal of a 25% margin on cooling power of 4 K/1 K temperature regions, a 25% margin on the heat load from Focal Plane Instruments (FPIs) at intermediated temperature region, to enhance the reliability of the mechanical cooler system, and to enhance feasibility of ground tests. Thermal property measurements of FRP materials are also important. This paper introduces details of the thermal design study for risk mitigation, including development of the truss separation mechanism, the cryogenic radiator, mechanical cooler system, and thermal property measurements of materials.