NOVEL SPACECRAFT RECOVERY, GUIDANCE AND CONTROL TO ENABLE KEPLER SCIENCE MISSION CONTINUATION

The Kepler spacecraft has completed more than three years and 15 science campaigns in its repurposed K2 mission. Using the two remaining reaction wheels and precise thruster pulses for control, the photometer studies fields of view in the ecliptic plane for up to 85 days at a time to find exoplanets, study stellar astrophysics and enable a community driven science program. The hydrazine fuel used for attitude control and momentum management is the most life-limiting consumable on the spacecraft. This paper will discuss ongoing operational efforts to minimize fuel consumption and maximize on-orbit lifetime. Recently, a safe mode control scheme utilizing only the two remaining reaction wheels was deployed on the vehicle. In the event of a fault, the spacecraft will enter and dwell in a power positive, safe state without using any fuel. This two wheel safe mode replaces thruster controlled safe mode which had the highest fuel burn rate of any K2 operational mode. Fuel consumption and thruster performance tracking have become paramount in the latter stages of the K2 mission. To improve insight into fuel consumption and thruster performance, new methodologies to analyze the unique thruster operations and monitor for end of life indicators have been developed. Predicting fuel exhaustion is critical to ensuring enough fuel is left in the tank to download the final science data from the vehicle. These on-orbit changes and ground analyses have resulted in the most recent science campaigns being the most fuel efficient campaigns in K2.