HII/L2 mission: future Japanese infrared astronomical mission

We present a conceptual design of a future Japanese IR astronomical satellite: the HIII/L2 mission. We propose a 'warm launch' cooled telescope; the telescope is to be launched at ambient temperature and is to be cooled in orbit to 4.5K by a modest cryogenic cooler with the help of radiative cooling. Since liquid helium and hence a heavy vacuum vessel are not longer required, the warm launch design reduces the weight of the satellite dramatically. We propose to launch this satellite into a halo orbit around S- E L2, one of the Sun-Earth Lagrangian liberation points. The S-E L2 is an ideal orbit for IR astronomy, since (1) radiative cooling can become very effective, and (2) by the Japanese H-IIA launching vehicle. This mission focuses on high-resolution mid- to far-IR observations with unprecedented sensitivity, since the large aperture reduces confusion noise and the cooled optics suppresses instrumental background radiation. The HII/L2 mission is an ideal observatory-type platform to make follow-up observations to the ASTRO-F/IRIS survey mission. The target launch year is 2010.