The search campaign to identify and image the Philae Lander on the surface of comet 67P/Churyumov-Gerasimenko

Abstract

, the Rosetta Philae Lander descended to make the first soft touchdown on the surface of a cometcomet 67P/Churyumov-Gerasimenko. That soft touchdown did occur but due to the failure in the firing of its two harpoons, Philae bounced and travelled across the comet making contact with the surface twice more before finally landing in a shaded rocky location somewhere on the southern hemisphere of the comet. The search campaign, led by ESA, involved multiple teams across Europe with a wide range of techniques used in support of it. This search campaign would continue through 2015 where a prime candidate on the surface was identified and on into 2016 to end on the 2nd of September 2016 when a definitive and conclusive image was taken of the lander on the surface of the comet, confirming the prime candidate to indeed be Philae. 1. The Philae landinga bounce into the unknown The Rosetta mission represented a Cornerstone of the ESA Horizon 2000 programme [1]. It was launched in March 2004 and arrived at its prime destination comet 67P/Churyumov-Gerasimenko (CG) in August 2014, after a 10 year cruise across the solar system. After arrival, activities immediately kicked off to select a landing site for the Philae Lander that had travelled the long journey with Rosetta [2]. With the landing site "Agilkia" chosen in September 2014 (Fig. 1), steps then took place to prepare for the separation of Philae a number of weeks later. Philae separated from Rosetta in the early hours of 12th of November 2014 and drifted down to the surface during a seven-hour descent phase. Communication between Rosetta and Philae took place using the "Electrical Support System" (ESS) located on Rosetta [3]. Contact with the ESS was established between Rosetta and Philae about

The interior of Comet 67P/C–G; revisiting CONSERT results with the exact position of the Philae lander

“…We initially assumed homogeneous dielectric properties for the entire sounded area of the cometary interior (Kofman et al 2015). In the simulations, the Philae lander is located on the surface near the coordinates derived from the 2016 September observations (O'Rourke et al 2019). Because our simulations depend strongly on the local environment of the lander, we used OSIRIS (Keller et al 2007;Jorda et al 2016) and NAVCAM images of the landing site, available from the Planetary Science Archive (PSA) of ESA, to select the lander location on the shape model that best reflects the local slopes of the actual landing site.…”

“…Because our simulations depend strongly on the local environment of the lander, we used OSIRIS (Keller et al 2007;Jorda et al 2016) and NAVCAM images of the landing site, available from the Planetary Science Archive (PSA) of ESA, to select the lander location on the shape model that best reflects the local slopes of the actual landing site. This location for the simulations is 13 m away from the OSIRIS location given in the PSA data base (O'Rourke et al 2019). However, considering the lateral sampling of ∼4 m on average (which can reach up to 10 m locally), the slight differences between the local ESOC (European Space Operations Centre) and Cheops/OSIRIS frames, and the differences between the shape models in use, this difference in the lander location is acceptable (Jorda et al 2016;O'Rourke et al 2019).…”

“…This location for the simulations is 13 m away from the OSIRIS location given in the PSA data base (O'Rourke et al 2019). However, considering the lateral sampling of ∼4 m on average (which can reach up to 10 m locally), the slight differences between the local ESOC (European Space Operations Centre) and Cheops/OSIRIS frames, and the differences between the shape models in use, this difference in the lander location is acceptable (Jorda et al 2016;O'Rourke et al 2019).…”

The CONSERT operations planning process for the Rosetta mission

“…OCN is made of two pairs of two cross dipoles, also providing a left-handed elliptic polarized wave 9 . When nominally landed, which was, unfortunately, definitely not the case for the 2014 landing 10 , the main part of the LCN transmitted signal power is directed to the ground, due to coupling with the ground and the platform structure 11 . This ensures the best link budget during the science operations when penetrating through the comet nucleus, but makes this link more difficult when OCN and LCN are operated in visibility.…”

Rosetta CONSERT Data as a Testbed for In Situ Navigation of Space Probes and Radiosciences in Orbit/Escort Phases for Small Bodies of the Solar System

“…Among the 10 scientific payloads onboard Philae [22,23] was the Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT), a VHF radar transponder, designed to sound the interior of the comet. Results from the CONSERT served as a key input to help locate Philae's position by determining the small zone where the lander came to a final rest [24][25][26][27]. The CONSERT instrument consisted of two parts: the CONSERT Orbiter (OCN) onboard the Rosetta spacecraft, and the CONSERT Lander (LCN) onboard the Philae lander.…”