Observation System of Radio Sources on the Moon by VLBI in SELENE project

1)H. Hanada, 2)T. Iwata, 1)N. Kawano, 1)K. Heki, 1)S. Tsuruta, 1)T. Ishikawa, 1)H. Araki, 1)K. Matsumoto, 3)Y. Kono, 2)Y. Kaneko, 2)M. Ogawa, 4)Y. Iijima, 5)Y. Koyama, 5)M. Hosokawa, 6)T. Miyazaki, 3)N. Namiki, 7)A. Sengoku, 8)Y. Fukuzaki, 9)T. Ikeda, 9)F. Fuke & RISE group

1)National Astronomical Observatory,
2)National Space Development Agency of Japan,
3)Kyushu University,
4)Institute of Space and Astronautical Science,
5)Communication Research Labolatory,
6)Kagoshima University,
7)Hydrographic Department,
8)Geographical Survey Institute,
9)NEC Corporation

VRAD (VLBI radio source on the Moon) mission measures angular distance between a radio transmitter on a lunar orbiter, that on the Moon and quasars by differential VLBI. This mission is mainly promoted by National Astronomical Observatory under SELenological and ENgineering Explorer (SELENE) project which is the first ISAS/NASDA joint lunar program. VRAD can measure amplitudes of the physical librations, gravitational harmonic coefficients of the Moon and lunar ephemeris with an accuracy one or two orders higher than before and will contribute not only to study of the interior of the Moon but also to establishment of reference frames. The radio transmitters emit three carrier waves in S-band (2212, 2218 and 2287 MHz) and one wave in X-band, and VLBI antennas on the Earth and a special recording system receive the waves and determine phase differences between them within 10 degrees. The radio transmitter on the Moon is surrounded by a thermal insulator suspended by strings and is operated with high energy density lithim batteries for longer than 2 months.