ESA GNC Conference Papers Repository

KAGUYA, which was called the SELenological and ENgineering Explorer (SELENE) in its development phase, is Japan’s first full-scale lunar explorer. The primary objectives of KAGUYA are the acquisition of scientific data related to the lunar origin and evolution and the development of technologies for future lunar exploration, such as reliable lunar polar orbit insertion and accurate three-axis attitude control in lunar orbit [1]. KAGUYA was launched using an H-IIA rocket on September 14, 2007 and inserted into the planned lunar transfer orbit (LTO). Subsequently KAGUYA conducted five orbital maneuvers in the lunar transfer orbit to reach the lunar orbit insertion point and did the first lunar orbit injection (LOI) maneuver on October 4, 2007, after which it entered the planned lunar polar orbit. Reliable lunar polar orbit insertion necessitates a reliable onboard flight system. Especially, the role of the attitude and orbit control system (AOCS) is important because the AOCS must control a sequence of orbital maneuvers and realize the accurate velocity increment for the orbital maneuver through accurate three-axis attitude control and variable thruster cut-off timing. Because orbit maneuvers are time-critical, the AOCS conducts orbital maneuvers automatically using stored maneuver parameters calculated by ground operation. For high-precision observations from lunar orbit, an accurate lunar centric pointing three-axis attitude control in lunar orbit is required for the AOCS. In addition, KAGUYA has various different phases of control before reaching the moon: sun acquisition, inertial frame pointing attitude control in lunar transfer orbit, attitude control at orbital maneuvers, attitude control for daughter satellite separations, and lunar centric pointing attitude control for lunar observation. In fact, the AOCS must realize these different requirements for different phases using the limited resources of KAGUYA satellite. Considering these system requirements and technical challenges for the AOCS, we designed and developed the simple but reliable and accurate KAGUYA AOCS. This paper first shows an outline of KAGUYA’s system and mission profile, then describes the KAGUYA AOCS and its control modes, and finally presents AOCS operation results during the lunar transfer phase and the lunar orbit injection phase.