Takao Nakagawa

The infrared space telescope SPICA, Space Infrared Telescope for Cosmology and Astrophysics, which features a 3m-class and 6K cryogenically cooled space telescope, is a next-generation astronomical project of Japan Aerospace Ex-ploration Agency (JAXA). The telescope and scientific instruments are cooled by a combination of an active (mechanical) cooling system and a passive (insulation and radiation) cooling system in the payload module. In this paper, the structural overview is described especially for the passive cooling system in the payload module and the summary of some experi-mental studies is presented.

Space Infrared Telescope for Cosmology and Astrophysics (SPICA) is an infrared IR astronomical satellite to be launched in 2022. It is equipped with sensitive IR sensors, cooled down to 4.5K. It also consists of a high-power X-band transmitting antenna used for downlink to the earth. Since energy leakage should be stringently suppressed from the antenna to the IR sensors, it is necessary to evaluate electromagnetic shielding effectiveness (SE) of structural materials of the satellite, including carbon fiber reinforced plastics (CFRP), multi-layer insulator (MLI), and aluminium plates connected with rivets. The CFRP and MLI were found to yield SE equivalent to aluminium. The SE of the connected aluminium plates increased with decreasing spacings of the rivets. Chromate conversion coating, providing higher surface conductivity than anodized aluminium surface, also enhanced the SE.

We present the overview and the current status of SPICA (Space Infrared Telescope for Cosmology and Astrophysics), which is a mission optimized for mid- and far-infrared astronomy with a cryogenically cooled 3.2m telescope. SPICA has high spatial resolution and unprecedented sensitivity in the mid- and far-infrared, which will enable us to address a number of key problems in present-day astronomy, ranging from the star-formation history of the universe to the formation of planets. To reduce the mass of the whole mission, SPICA will be launched at ambient temperature and cooled down on orbit by mechanical coolers on board with an efficient radiative cooling system, a combination of which allows us to have a 3-m class cooled (6K) telescope in space with moderate total weight (3.7t). SPICA is proposed as a Japanese-led mission together with extensive international collaboration. ESA's contribution to SPICA has been studied under the framework of the ESA Cosmic Vision. The consortium led by SRON is in charge of a key focal plane instrument SAFARI (SPICA Far-Infrared Instrument). Korea and Taiwan are also important partners for SPICA. US participation to SPICA is under discussion. The SPICA project is now in the "risk mitigation phase". The target launch year of SPICA is 2022.