PHILAE Lander: a scheduling challenge

Rosetta is an ambitious mission launched in March 2004 to study the nucleus as well as the coma of comet 67P/Churyumov-Gerasimenko. It is composed of a space probe and a Lander, Philae. The space probe will reach the vicinity of the comet in spring 2014 when it will start to investigate Churyumov-Gerasimenko with remote sensing instruments. Thanks to the obtained data the shape and density of the comet will be defined and an appropriate landing site will be selected, PHILAE lander will be the first equipment to land on a comet nucleus. This spectacular phase is expected to take place in November 2014 at a distance of about 3 AU from the sun. During its descent and once attached to the comet, the lander will begin its science mission. So it will perform detailed and innovative in-situ investigations on the comet’s surface to characterize the nucleus by 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 is to schedule and optimize the operational science activities of the 10 lander experiments and then to provide it to the Lander Control Center (LCC) located in DLR Cologne. Nevertheless the specific context of the Rosetta mission makes it more complex than for usual spacecraft or landers. Indeed the teams in charge of the Philae activity scheduling have to cope with huge constraints in term of energy, data management, asynchronous processes and co-activities or exclusions between instruments, ... In addition to these numerous constraints it is important to note that the comet and its environment will remain unknown until the delivery time and that the landing site will be selected a short time before landing. This paper will explain the specific context of the Lander mission and all the constraints that the activity scheduling has to face to fulfill the scientific objectives specified for PHILAE. A specific tool was developed by CNES and used to design the complete sequence of activities on the comet with respect to all the constraints. The current baseline scenario designed this way will also be detailed to highlight the difficulties and challenges that the operational team has to face. Moreover the example of an on-comet sequence will be used to highlight the fact that some activities might be modified and demonstrate how it is important to be prepared to this kind of adaptation during operations according to received information. Indeed as for every mission of exploration some unexpected events should happen and will induce a flexibility concept in the operations.