THE SELENE MISSION: PRESENT STATUS AND SCIENCE GOALS

Introduction: Lunar orbiting satellite SELENE has completed after final integration tests of thermal-vacuum and electromagnetic compatibility in the end of February 2007. Just now pre-shipping reviews are being carried out before moving satellite to launch site of JAXA TKSC for 2007 summer launch. The SELENE has started in 1998 FY as a joint mission of ISAS and NASDA, which have been merged into a space agency JAXA in October 2003. The SELENE project is certainly identified as a JAXA’s science mission. End-to-end GDST (Ground Data System Test) has also ended successfully in SOAC (SELENE Operation and data Analysis Center) of Sagamihara/JAXA. Science Instruments and Observations: 14 science instruments and high definition TV (HDTV) camera are onboard the spacecrafts for science data collection and public outreach. The characteristic specifications of instruments are summarized in Table 1 by categorizing with observation purposes. Global mapping of elemental abundance on the lunar surface will be made by XRS and GRS using advantages to each instrument. Global mapping of major elements by XRS has never been tried till now, although GRS mapping have performed in the Lunar Prospector mission[1]. Only 10 percentages of the lunar surface has been analyzed in the Apollo XRSs [2]. Global mineralogical distribution will be mapped by MI and SP measuring reflectance twodimensionally and one-dimensionally of the lunar surface, respectively. Topographic measurement to study the surface evolution of the Moon will be participated by three instruments of TC, LRS, and LALT. Stereo images of the TC by two CCD will be employed for global map of digital elevation (DEM). The LALT is a conventional altimeter using Nd:YAG laser. The LRS sounds lunar surface and subsurface within about 5 km to study lunar topography and tectonic activity of subsurface. The LRS equips function receiving radio waves to 30 MHz to detect natural waves emitted from Jupiter, Sun and others in electromagnetically quiet environment of lunar farside. Two pairs of LRS bi-stem antennas with tip to tip length of 30 m will be extended on circular orbit of 100 km altitude. VRAD and RSAT will be onboard the Rstar, Vstar, and the main orbiter to determine precise gravity field of the Moon. Two radio sources emit three S-band and an X-band radio waves to determine the satellites positions with accuracy of 10 cm by differential VLBI technique between subsatellites and ground VLBI stations referencing with the signals of pulsars. In order to track main orbiter flown in farside the RSAT will be used to relay S-band range-rate signals. 4-way Doppler technique between main orbiter and a ground station via Rstar will determine the gravity field of the farside. This is first experiment which has never been performed till now. LMAG, CPS, PACE, RS, and UPI will be employed to observe the environments of the Moon and the Earth. The LMAG will be used to measure magnetic field distribution or local remnant magnetization on the Moon with accuracy of 0.5 nT. In order to measure with reliable accuracy the magnetometer will be attached on the top of extendable mast of 12 m length so distant to alleviate effects of electromagnetic disturbance from spacecraft. Primary purpose of CPS is measure the environment of charged particle such as protons from cosmic-ray origin. This instrument may also detect alpha-ray particles from the lunar faults which presumably originated by tectonic activity. The PACE will investigate sorts, energy, and incident angles of environment particles of ions, electrons, and neutral atoms using mass spectrometers of time-of-flight type. The RS team will try to confirm the existence of tenuous ionosphere of the Moon, detection of which was reported by Soviet lunar orbiter Luna 19. S-band and X-band radio waves passing through the limb of the Moon emitted from VRAD2 on Vstar will be received on ground stations to detect which any variation exists in frequency of waves. The UPI instrument is an imager to observe plasma phenomena of terrestrial upper atmosphere such as aurora from lunar orbit. HDTV movies of “Earthrise” from horizon of the Moon, vivid lunar surface etc. will be broadcasted for public outreach. Detectors of these instruments are allocated on the surface panels of SELENE spacecraft as shown in Fig. 1. The figure shows the schematic diagram of SELENE spacecraft on transfer orbit to the Moon before release of subsatellites. Most of instruments will be fixed on the +Z panel which directs to the Moon to observe the lunar surface. Detectors observing the Sun and space are put on the –Z panel. Electronics boxes of the instruments are positioned inside of panels considering thermal release and noise reduction.