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Philae, a comet Lander, part of the ESA Rosetta mission successfully landed on comet 67P/Churyumov- Gerasimenko on November 12th, 2014. After several (unplanned) bounces it performed a First Scientific Sequence (FSS), based on the energy stored in it's on board batteries. All ten instruments of the Philae payload have been operated at least once. Due to the fact that the original landing site was poorly illuminated, Philae went into hibernation on November 15th, but signals from the Lander were received again in June and July 2015. However, various attempts to re-establish reliable and stable communications links, failed. Analysis of the data gained during FSS, and during the contacts in June and July 2015 allows conclusions on the state of Philae. By now, images from the OSIRIS camera aboard the Rosetta Orbiter have allowed the identification of the exact position of Philae and its attitude, relative to the local surface terrain. The paper also gives an overview of the implications of Philae results for future engineering comet models, required particularly for the design of in-situ (landing) or sample return missions. Rosetta is an ESA mission with contributions from its member states and NASA. Rosetta's Philae Lander is provided by a consortium led by DLR, MPS, CNES and ASI with additional contributions from Hungary, UK, Finland, Ireland and Austria.

Philae is a comet Lander, part of Rosetta which is a Cornerstone Mission of the ESA Horizon 2000 programme. Philae successfully landed on comet 67P/Churyumov-Gerasimenko on November 12th, 2014 and performed a First Scientific Sequence, based on the energy stored in it’s on board batteries. All ten instruments of the payload have been operated at least once. Due to the fact that the final landing site (after several bounces) was poorly illuminated, Philae went into hibernation on November 15th, and the teams hoped for a wake-up at closer heliocentric distances

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 mission is a series of premieres: among others, first probe to escort a comet, first time a landing site is selected with a so short notice, first time a lander has landed on a comet nucleus. The space probe Rosetta reached the vicinity of the comet in spring 2014 when it has started to study Churyumov-Gerasimenko with remote sensing instruments. An intense observation phase followed to be able to select a landing site for the Lander. And in November 2014, at a distance of about 3 AU from the sun, Philae has reached its destination on the surface of the comet 67P. Once stabilized on the comet, the lander has performed its “First Science sequence”. Philae’s aim was to perform detailed and innovative in-situ experiments on the comet’s surface to characterize the nucleus by performing mechanical, chemical and physical investigations on the comet surface. The main contribution to the Rosetta lander by the French space agency (CNES) is the Science Operation and Navigation Centre (SONC) located in Toulouse. Among its tasks is the scheduling of the scientific activities of the 10 lander experiments and then to provide it to the Lander Control Centre (LCC) located in DLR Cologne. Nevertheless, the specific context of the Rosetta mission made this task even more complex if compared to usual spacecraft or landers: indeed the teams in charge of the Philae activity scheduling had to cope with huge constraints in term of energy, data management, asynchronous processes and co-activities or exclusions between instruments. In addition to these huge constraints it is important to note that the comet, its environment and the landing conditions remained unknown until the separation time and that the landing site was selected a short time before it had to take place and when the baseline operational sequence was already designed. This paper will explain the specific context of the Rosetta lander mission and all the constraints that the activity scheduling had to face to fulfil 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 constraints. The baseline scenario designed this way will also be detailed to highlight the difficulties and challenges that the operational team had to face. A specific focus will be given on the landing site selection and the impacts on the scientific operations scheduling. Moreover the actual sequence performed on the comet will also be detailed and analysed to deduce the lessons that could be learned from such an unprecedented endeavour. Indeed as for every mission of exploration the flexibility concept was anticipated but had to face unexpected events.