Orbit determination of HAYABUSA from the launch to the asteroid arrival

HAYABUSA, which was launched in May 2003, is the first asteroid sample return mission in the world. It has arrived at its destination, Asteroid (25143) Itokawa, at the beginning of September 2005 successfully. HAYABUSA has an ion engine system (IBS) as the main thrusting system and it makes difficult to carry out the orbit determination because of the continuous low acceleration. We have tried many attempts to estimate the acceleration by IES. However, the accuracy of the orbit determination is not good enough when IBS is working, so we make ballistic period of at least three passes once in three weeks or so. We carry out accurate orbit determination at the ballistic period, and we propagate the orbit by using the telemetry information of IBS with some correction by estimating the acceleration by IBS. By this way we have carried out the orbital operation of HAYABUSA. We summarize here the status of the estimation of IBS acceleration. There are several important phases for the orbit operation, such as the launch, the earth swingby, the solar conjunction, and the asteroid arrival. The earth swingby was done on 19 May 2004, and it was successful. We were able to put the spacecraft into the orbit that approach to Asteroid Itokawa. In July of 2005, the solar conjunction occurred and HAYABUSA was opposite side of the Sun. We were able to go through the solar conjunction without any problem, and after that we carried out the optical navigation by using the optical camera on board. In this paper, we also summarize the results of our orbit determination at the launch, the earth swingby, and the solar conjunction. The first result of the optical navigation is mentioned briefly.