HII/L2 mission:
future Japanese infrared astronomical mission
Takao Nakagawa, T. Nakagawa,
M. Hayashi,
M. Kawada,
H. Matsuhara,
T. Matsumoto,
H. Murakami,
H. Okuda,
T. Onaka,
H. Shibai,
and M. Ueno
Submitted to Space Telescopes and Instruments V,
SPIE Proc. 3356, ed. P. Y. Bely & J. B. Breckinridge, 1998
abstract
We present a conceptual design of a future Japanese infrared astronomical satellite: the HII/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 no 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 infrared astronomy, since (1) radiative cooling can become
very effective, and (2) long-integration observations become possible. A 3.5 m class telescope
can be put into a halo orbit around S-E L2 by the Japanese H-IIA launching vehicle. This mission
focuses on high-resolution mid- to far-infrared 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.