Abstract
The Japanese lunar mission, SELENE (Kaguya) consists of a Main satellite and two small satellites, Rstar and Vstar. In S-band same-beam VLBI observations of Rstar and Vstar, phase fluctuations caused by the atmosphere, ionosphere and instruments were reduced to a low level of 1deg～2 deg, and the S-band differential phase delay between Rstar and Vstar was obtained with an error of 1 pico-second. We corrected the long-time atmospheric and ionospheric delays by using GPS techniques. According to the VLBI observation results up to February 2008, we changed the VLBI observation method that the telescope tracked the midpoint of Rstar and Vstar even if when the separation angle is as large as 0.56 deg. From March 2008, the chances for S-band same-beam VLBI observations are thus much increased and more data were obtained for orbit determination and estimating the global lunar gravity field model. We performed orbit determination for Rstar and Vstar, the accuracy was improved from a few tens meters when only using Doppler and range data, to a level of about 10 m when S-band same-beam VLBI data are also used.
