Results obtained by geodetic instruments of SELENE (KAGUYA)

Abstract

Japanese lunar explorer SELENE (KAGUYA) was equipped with 14 instruments for various measurements of the Moon. Three of these instruments took geodetic measurements of the Moon. These were two sub-satellites and a laser altimeter. The main results obtained by the instruments are: (1) precise orbit determination with an accuracy of ten meters by Doppler and same-beam VLBI; (2) the first precise gravity fields on the lunar far side by 4-way Doppler measurements; (3) the first topography in latitudes higher than 86 degrees; (4) a global map of the gravity anomaly by using the global topography and the global gravity fields; (5) a global map of the lunar crustal thickness and (6) an illumination rate map in the north and south polar regions. SELENE, gravity field, lunar far side, topography, gravity anomaly, crustal thickness, illumination rate PACS: 96.12.Bc, 96.12.Qr, 95.10.Eg, 95.75.De SELENE was successfully launched in September 2007together with two sub-satellites. The SELENE mission has been proposed primarily to study the origin and evolution of the Moon by means of the global characterization of the lunar surface and investigations of its interior. A wide variety of observations by 14 instruments was carried out for about one year in order to perform these aims. These observations can be classified into five fields. Figure 1 shows relations among the observations by SELENE, scientific knowledge of the Moon to be obtained from the observations and our aims (lunar origin and evolution) [1]. The geodetic instruments among the 14 ones are two sub-satellites and a laser altimeter. Geodetic observations by them played the roles that are shown in the hatched blocks in Figure 1. Strategy in geodetic observations of SELENEThere are not so many methods to study the interior of a planet or the Moon. For example, observations of lunar rotation and moonquakes have revealed the Moon's internal structure. Lunar gravity fields enabled us to better under- Figure 1 Observations by SELENE and scientific knowledge to be obtained. The hatched blocks are items with relation to geodetic measurements.

The Chang’E-1 orbiter plays a distinctive role in China’s first successful selenodetic lunar mission

“…Such orbit information has less accuracy, using only the old lunar gravity field of LP100J and not all of the systematic effects having been removed from the TT&C data when estimating the satellite orbits during the normal mission period. Subsequent to the extended mission of Chang'E-1, the Japanese SELENE team [32] estimated a new lunar gravity model SGM100H [19] including detailed farside gravity information. Additionally, a joint Chinese-Japanese research team combined the tracking data metric of LP, SELENE and Chang'E-1 to provide a new lunar gravity model CEGM-02 [26] that surpassed other models at the very long wavelength.…”