Direct measurement of the gravity field in far-side of the Moon
Updated : 2008.01.22
Observation date : 2007.11.06

As the part of the initial functional check out, the local gravity field of the far-side of the Moon is observed by measuring the disturbance of the orbit of the "KAGUYA" Main Orbiter through the relay satellite "OKINA" (Rstar) on November 6, 2007. This is the world's first direct measurement of the gravity field in far-side of the Moon.

When a lunar orbiting satellite flies over the areas with relatively higher gravitational forces, a lunar orbit satellite is pulled, that satellite is accelerated and its orbit may be changed. The lunar underground structure, which cannot be direct observed, can be estimated by a continuous profiling of location and speed changes of the lunar orbit satellite.

While the main satellite "KAGUYA" flies over the far side of the Moon, KAGUYA cannot receive uplink radio signal from the JAXA Usuda Deep Space Center (UDSC; Saku-city, Nagano pref., Japan) directly. During that period, the "OKINA" relays the uplink radio signal to the "KAGUYA".

By analyzing the orbital changes of the "KAGUYA" around the far-side of the Moon, the accurate lunar far side gravity field will be derived and this direct gravity filed measurement is the first time in the world.

Data will be processed by RSAT/VRAD team.