On-board and ground operations of MUSES-C

The MUSES-C spacecraft was launched on May 9, 2003 and has been propelled by microwave discharge ion engines. The mission duration is four years in total and most of it is the cruising phase driven by ion propulsion. After one-year acceleration it succeeded the Earth swing-by on May 19, 2004 and still on the way to the asteroid "ITOKAWA". Active thrust vector control contributes to keep the reaction wheels within an appropriate rotation rate. The hydrazine thruster firing tunes off the ion engines before it and restart them again after it. Depending on the operation of ion engines the heater power is adjusted. These operations are autonomously controlled on the spacecraft without supervisions from Earth. A ground operation system that integrates all the process required for ion engine operations such as orbit synthesis, orbit determination, operation scheduling, command generation and telemetry data analysis has been developed. Automation of on-board and ground operations saves the operation cost and time, and makes the operation stable and reliable.