The present status of the Japanese Penetrator Mission: LUNAR-A

The scientific objective of the LUNAR-A Japanese Penetrator Mission is to explore the lunar interior by seismic and heat-flow experiments. Two penetrators containing two-component seismometer and heat-flow probes will be deployed from a spacecraft onto the lunar surface, one on the nearside and the other on the farside of the moon. The data obtained by the penetrators will be transmitted to the ground station by way of the LUNAR-A mother spacecraft orbiting at an altitude of about 200 km. The seismic observations are expected to provide key data on the size of the lunar core, as well as data on the deep mantle structure. The heat-flow measurements at two different sites will also provide important data on the thermal structure and bulk concentrations of heat-generating elements in the Moon. These data will provide much stronger geophysical constraints on the origin and evolution of the Moon than has ever been obtained. The LUNAR-A mission was supposed to be launched in 2004. However, a malfunction of spacecraft subsystem and technical issues for penetrator system occurred during the course of the qualification level test. Therefore, further improvements and some modifications were considered to be required for reliability and robustness. The development of the mother spacecraft was temporarily suspended, while we have put a three-year program into effect to solve the penetrator technology issues.