Contingency operations design for Korea pathfinder lunar orbiter

Korea pathfinder lunar orbiter (KPLO) is a spacecraft developed by Korea Aerospace Research Institute and performs lunar surface imaging, investigation of permanently shadowed regions, and scientific measurement in a lunar orbit. KPLO approaches the Moon through a 3.5 phasing loop transfer orbit for about a month after launch. Then KPLO enters the lunar orbit of 100 km altitude through the four lunar orbit insertion maneuvers. In a mission orbit, the nominal mission phase begins after a month of commissioning phase for in-orbit test of the spacecraft bus and the instruments. Various contingency can occur in the transfer orbit and mission orbit. If it is not resolved properly in a timely manner, it can cause serious consequences such as lunar orbit insertion failure, battery depletion or communication failure. One of critical contingency in the transfer orbit is safe mode transition of the spacecraft bus during the first lunar orbit insertion maneuver. If the planned delta-v is not obtained in LOI#1, the orbiter will not be captured in the lunar orbit, and even if it is captured, it will need additional fuel to enter the mission orbit. One of critical situation in the mission orbit is that unexpected spacecraft malfunction occurred during the lunar eclipse period and the spacecraft cannot recover its electrically or thermally safe status after the lunar eclipse. Therefore, contingency situations that may arise in transfer orbit and mission orbit should be identified and appropriate operation method should be designed in on-board logic and ground procedures. In this paper, we present the design results of the contingency operation against the critical situations that may occur in KPLO.