The Orbit Determination of the CHANG´E-1 Lunar Orbiter by VLBI

A long-term lunar exploration project named Chang´E project is going on in China. The Chang´E-1, the first Chinese lunar orbiter is launched in 2007. The VLBI (very long baseline interferometry) technique is used for the precise orbit determination (OD) of the Chang´E-1 spacecraft combined with the conventional tracking technique for both navigation and scientific purposes. Recently, a VLBI network of four stations has been constructed in China, located at Shanghai (25m), Beijing (50m), Kunming (40m) and Urumqi (25m), respectively. A VLBI data processing center equipped with a hardware five-station VLBI correlator, a software four-station correlator and other data processing and analysis equipments is at Shanghai Astronomical Observatory, CAS, in Shanghai. The real-time VLBI technique is used for timely VLBI data transferring from stations to the data processing center and quick data correlation and the OD. In order to demonstrate the capability of VLBI OD operation before the launching of the Chang´E-1, a series of VLBI experiments with the Smart-1, an ESA lunar orbiter have been carried out. The accuracy of several tens meters for the position and a few centimeters per second for the velocity of a lunar orbiter has been demonstrated by those Smart-1 S-band VLBI experiments