Browsing by Author "Knapmeyer, Martin"

The landing of Philae on comet 67P/Churyumov-Gerasimenko is scheduled for November 12th, 2014. Each of the three landing feet houses in one sole a tri-axial acceleration sensor of the Comet Acoustic Surface Sounding Experiment (CASSE). They will thus be the first sensors to be in mechanical contact with the comet surface. CASSE will be in listening mode to record the deceleration of the lander when it impacts with the comet at a velocity of approx. 1 m/s. The signals are used to discern from these data whether the selected landing place is of icy or sandy nature. Here, a deeper analysis of this data yields information on the reduced elastic-plastic modulus of the comet's surface material. (C) 2014 Elsevier Ltd. All rights reserved.

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 similar to 20 cm thick, possibly on top of a more rigid layer. The final landing site, Abydos, has a hard surface.

After the final landing of Philae at the Abydos site on comet 67/P Churyumov-Gerasimenko, the MUPUS (Multipurpose Sensors for Surface and Sub-Surface Science) device started hammering itself into the cometary ground on 14th November 2014, and continued hammering for more than 3 h. During this period, the CASSE (Comet Acoustic Surface Sounding Experiment) instrument, part of SESAME (Surface Electric Sounding and Acoustic Monitoring Experiment), was listening to the hammer strokes of MUPUS, which was the strongest available source for a seismic-acoustic experiment to determine mechanical properties of the ground. All sensors survived the multiple touchdowns of Philae undamaged and provided recordings of 14 hammer strokes at audible frequencies. The data suggests that Philae was slightly rocking or swinging during the initial phase of the experiment, finally finding an attitude that not only stopped this motion but also improved the coupling of sensors to the ground and thus the recordings. The experiment provides several lessons that might be useful for the development of similar experiments on future spacecraft. The most serious issues concerning the CASSE recordings are clock accuracy and synchronicity and the timing of the source. Future designs may want to consider additional sensors in close proximity to the source, and direct communication between experiments to overcome this. The present design allows the evaluation of arrival time differences only, rather than absolute travel times. In this contribution, we focus on the technical and operational aspects of this experiment. A scientific evaluation of the data received will follow in a second paper. (C) 2016 IAA. Published by Elsevier Ltd. All rights reserved.

This contribution corrects a table given in a previous contribution. (C) 2016 Published by Elsevier Ltd. on behalf of IAA.