The Philae lander, part of the Rosetta mission to investigate comet 67P/Churyumov-Gerasimenko, was delivered to the cometary surface in November 2014. Here we report the precise circumstances of the multiple landings of Philae, including the bouncing trajectory and rebound parameters, based on engineering data in conjunction with operational instrument data. These data also provide information on the mechanical properties (strength and layering) of the comet surface. The first touchdown site, Agilkia, appears to have a granular soft surface (with a compressive strength of 1 kilopascal) at least ~20 cm thick, possibly on top of a more rigid layer. The final landing site, Abydos, has a hard surface.
This article describes the characterization activities of the landing sites currently envisaged for the Lunar Lander mission of the European Space Agency. These sites have been identified in the South Pole Region (-85° to -90° latitude) based on favourable illumination conditions, which make it possible to have a long-duration mission with conventional power and thermal control subsystems, capable of enduring relatively short periods of darkness (in the order of tens of hours), instead of utilising Radioisotope Heating Units. The illumination conditions are simulated at the potential landing sites based on topographic data from the Lunar Orbiter Laser Altimeter (LOLA), using three independent tools. Risk assessment of the identified sites is also being performed through independent studies. Long baseline slopes are assessed based on LOLA, while craters and boulders are detected both visually and using computer tools in Lunar Reconnaissance Orbiter Camera (LROC) images, down to a size of less than 2 m, and size-frequency distributions are generated. Shadow hazards are also assessed via LROC images. The preliminary results show that areas with quasi-continuous illumination of several months exist, but their size is small (few hundred metres); the duration of the illumination period drops quickly to less than one month outside the areas, and some areas present gaps with short illumination periods. Concerning hazard distributions, 50 m slopes are found to be shallow (few degrees) based on LOLA, whereas at the scale of the lander footprint (~5 m) they are mostly dominated by craters, expected to be mature (from geological context) and shallow (~11°). The preliminary conclusion is that the environment at the prospective landing sites is within the capabilities of the Lander design.
Rosetta is a Cornerstone Mission of the ESA Horizon 2000 program. After rendezvousing with comet 67P/Churyumov-Gerasimenko in August 2014 and a 10 year cruise it started to study both its nucleus and coma with an orbiting spacecraft. The Lander, Philae, will land on November 12th and perform in-situ studies of the cometary material with a payload consisting of 10 scientific instruments. Rosetta and Philae have been in hibernation until January 20, 2014. After the successful wakeup they underwent a post-hibernation commissioning. The orbiter instruments (like e.g. the OSIRIS cameras, VIRTIS, MIRO, Alice and ROSINA) characterized the target comet and its environment to allow landing site selection and the definition of a separation, descent and landing (SDL) strategy for the Lander. By September 2014 our previously poor knowledge of the characteristics of the nucleus of the comet has increased drastically and the nominal and backup landing could be selected. The nominal site, as well as the corresponding descent strategy have been confirmed in mid-October, one month before the landing. The paper summarizes the selection process for a landing site and the planning for Separation-Descent-Landing (SDL).
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