Philae localization from CONSERT/Rosetta measurement

Abstract

On 12 November 2014 at 15:34 UTC, after a 7-hour descent, the Philae lander made contact with the surface of the comet Churyumov-Gerasimenko (67P/CG) in the centre of the intended landing zone. Following the failure of its anchoring systems, it bounced and continued to fly ballistically. A couple of hours later, telemetry transmitted to Rosetta showed that Philae was stabilized on the surface and working properly although its precise and final location was and still is not known. (Biele et al, 2015). From the morning of 13 November 2014, CONSERT data enabled an initial estimate to be made of Philae's location based on signals propagated through the 67P/CG nucleus. This rough location was then refined through three sets of measurements carried out during periods of direct visibility between Rosetta and Philae during the Philae's First Science Sequence (FSS) on 13 and 14 November. This paper presents these measurements and the estimate of the final position of Philae in November 2014.

The Philae lander mission and science overview

“…From further modelling (assuming adequate mean values for the density, specific heat and ice-to-dust mixing) the thermal conductivity of the soil at Abydos is constrained to be 0.02-0.06 W m −1 K −1 and the bulk porosity to be 40-55% [49]. The latter value range falls clearly below estimates for the bulk porosity of the nucleus interior ( [19]; see also §3b) and suggests processing of the surface material and increased compactness, most likely due to a kind of 'thermal' sintering due to cometary activity at and underneath the surface.…”

“…Furthermore, the instrument also allowed measurements of the distance between orbiter and lander during the descent and during FSS (in total three epochs on 13 and 14 November 2014). From the latter data, the identification the Philae location at the Abydos site [19] was accomplished with uncertainties of about 22 × 106 m (see yellow region in [19]). Owing to the lander hopping and the resulting landing site location (Abydos), and due to the pre-programmed measurement timing [35], the CONSERT sensing of the 67P interior relates mostly to the 'head' of the nucleus body.…”

“…structures, in the electric permittivity of the material and/or reflections of sounding waves. The figure is adapted from Kofman et al[19]. (Online version in colour.…”

Rosetta Lander – Landing and operations on comet 67P/Churyumov–Gerasimenko

“…Although the position of Philae on the comet was constrained rather well, using images taken with the cameras aboard the Orbiter as well as CONSERT ranging data [3,20,24] and its orientation was determined using ROMAP measurements [25], the uncertainties regarding the surrounding terrain, illumination during seasonal changes and thermal input from the comet environment were rather high. Consequently, it was impossible to give exact predictions on when the Lander would have sufficient power to boot and when radio contact could be possible again.…”

A radar package for asteroid subsurface investigations: Implications of implementing and integration into the MASCOT nanoscale landing platform from science requirements to baseline design

“…Assuming a full 3D coverage of the body, the radar determines 3D structures such as deep layering, spatial variability of the density, of the block size distribution and of the permittivity. As a beacon on the surface of Didymoon, it supports the determination of the binary system's dynamic state and its evolution induced by the DART impact (a similar approach as used for the localization of the Philae lander during the Rosetta mission [30]).…”