Rosetta Lander - Philae: Status after First Landon on a Comet

Kurzfassung

Rosetta is a Cornerstone Mission of the ESA Horizon 2000 programme [1,2]. In August 2014 it did rendezvous with comet 67P/Churyumov-Gerasimenko (CG) after a 10 year cruise. Both its nu-cleus and coma have been studied allowing the selec-tion of a landing site for Philae [3], the lander which successfully landed on the comet on November 12, 2014. It did, however, bounced off again and only came to rest after a leap of about 2 hours, approximate-ly one kilometer from the originally targeted site. Phi-lae was operational for almost 64 hours after separation and provided unique information from the surface of the comet. All ten instruments aboard could be operat-ed at least once. Descent and Landing: After injection of the Ro-setta spacecraft into the delivery orbit, Philae was ejected with a separation velocity of 18.76 cm/s on November 12th, 2014 at 8:35 UTC. This maneuver was performed perfectly, leading to a touch-down, about 7 hours later, at 15:34:04, only 51 seconds (!) before the precalculated landing time. The touch-down signal was received, the lander switched into the “on-comet mode” and started its first scientific sequence. However, the anchoring harpoons have not been fired and a cold gas system, intended to provide hold-down thrust could not be activated. Consequently, Philae bounced off the surface and was ballistically drifting above the comet surface. After 1:50 hours the Lander came to its final rest, after two more surface contacts. The Lander is now at a poorly illuminated location, the solar generator apparently provides power for only 1:20 hours per comet rotation. Fortunately communica-tions link with the Orbiter was possible very similar to the predicted time-slots. [4,5] Lander Search and Attempts for Re-activation: For the search of the lander and in order to re-construct the trajectory and bouncing, OSIRIS images (some of them showing the lander, shadow or footprints.), CONSERT ranging data, landing gear and solar gener-ator HK data as well as data from ROMAP, MUPUS, ROLIS and SESAME have been used. Consequently, the position and attitude of the Lander is fairly well determined, however it could not be identified on any of the OSIRIS NAC images, yet. Although Philae could not stay active after the bat-teries were depleted in November, there is a good chance for re-establishing contact, when comet and Lander are closer to the sun. A first attempt in March 2015 was not successful but by the time of the confer-ence (in June the heliocentric distance of 67P is only 1.45 AU, less than half as at the time of landing) we hope to be able to report on new data from Philae. Achnowledgements: 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 contri-butions from Hungary, UK, Finland, Ireland and Aus-tria. References: [1] Glaßmeier, K.-H., Böhnhardt, H., Koschny, D., Kührt, E. and Richter I., (2007) Space Science Rev. 128, pp. 1-21. [2] Biele, J. and Ulamec, S. (2008) Space Science Rev. 138, 275-289. [3] Ulamec, S. et al. (2015) Acta Astron., Vol. 107, pp. 79-86. [4] Ulamec, S. et al., Philae – First Landing on a Comet, 46th Lunar and Planetary Science Conference, abstract# 1121, Houston, 2015, [5] Biele, J. et al. The landing(s) of Philae and Inferences on Comet Surface Mechanical Properties, submitted to Science, 2015