Improvements in lunar gravity field modeling and orbit determination from SELENE multi-satellite tracking data types

The launch of SELENE, which acquired the first direct tracking data over the farside of the Moon by the use of 4-way Doppler data between a relay satellite and the main satellite, has resulted in a dramatic improvement of the knowledge of the global lunar gravity field[1,2]. In addition to the 4-way Doppler data, same-beam differential VLBI data between the two sub-satellites and two stations on Earth were also collected using the VERA network, and foreign stations in two international campaigns. The strength of differential VLBI data derives from the differencing out of common measurement errors, resulting in a precise measurement. Together with the SELENE 2-way and 4-way tracking data and historical tracking data, the VLBI data were processed into a new lunar gravity field model called SGM100i[3] (Fig. 1). The use of VLBI data allow longer arc lengths for the subsatellites, increasing the sensitivity with respect to the lower degrees of the gravity field model. The resulting model shows a drastically improved performance in orbit determination, especially for edge-on geometries (where the satellite orbits over the deep farside). Correlations with topography also show an increase over the farside.