PHILAE Lander: Science scheduling challenge and lessons learned

摘要

Rosetta is an ambitious mission launched in March 2004 to study the nucleus as well as the coma of the comet 67P/Churyumov-Gerasimenko. It is composed of a space probe and the Philae Lander. The space probe has reached the vicinity of the comet in spring 2014 and is investigating Churyumov-Gerasimenko with remote sensing instruments. On November 12th 2014 PHILAE lander was the first equipment to land on a comet nucleus. This spectacular event occurred at a distance of about 3 AU from the sun. Once landed on the comet surface the lander has begun its science mission, performing mechanical, chemical and physical investigations on comet surface. The French space agency (CNES) is contributing to the mission by providing the Science Operation and Navigation Centre (SONC) located in Toulouse. One of its tasks was to schedule and optimize the operational science activities of the 10 lander experiments in coordination with the Lander Control Center (LCC) located in DLR Cologne. Huge constraints in term of energy available, data flow management, asynchronous processes, co-activities or exclusions between instruments and undetermined landing configuration made the scheduling task even more complex compared to "usual" spacecraft. This paper will explain the specific context of the Lander mission and all the constraints that the activity scheduling had to face to fulfil the Philae scientific objectives. A specific tool was developed by CNES and used to design the sequences of on comet activities with respect to all the constraints. The science scenarios defined before Landing and the ones finally applied once landed will be detailed to highlight the difficulties and challenges the operational team had to face. Moreover the paper will stress the importance of the flexibility concept in the design of the science operation and of being prepared to deal with unexpected situation.