Rosetta-Lander: On-Comet Operations Execution and Recovery after the Unexpected Landing

Abstract

Philae’s landing on comet 67P/Churyumov–Gerasimenko on 12 November 2014 was one of the main milestones of the European Rosetta mission. The nature of Philae’s mission, to land, operate and survive on comet 67P, required a high degree in autonomy of the on-board software and of the operations scheduling and execution concept. Philae’s baseline operations timeline consisted of predefined and validated blocks of instrument deployments and scientific measurements. These were supported by subsystem activities such as rotation and lifting of the main body relative to the landing gear to allow for specific instrument deployment or in order to cope with the unknown attitude after landing. The nominal descent was followed by an unforeseen rebound at touchdown, lifting Philae again from the comet surface to enter a two-hour phase of uncontrolled flight over the comet surface. Philae’s unknown final landing site, unfavorable attitude with respect to the local surface, bad illumination and lack of anchoring required a complete rescheduling of the baseline timeline. The autonomy offered by the system and the predefined contingency operations were exploited by the operations team to maximize output despite this undesirable state. Implementation of the rescheduling to allow a maximum scientific output, despite the limitations due to unknown communication windows, unknown orientation with respect to the comet surface, the associated risks of any mechanisms activation, the lack of sufficient solar power and limited battery lifetime, is described and elaborated.