Rosetta lander Philae: Flight Dynamics analyses for landing site selection and post-landing operations

Abstract

On the 12th of November 2014, The Rosetta Lander Philae became the first spacecraft to softly land on a comet nucleus. Due to the double failure of the cold gas hold-down thruster and the anchoring harpoons that should have fixed Philae to the surface, it spent approximately two hours bouncing over the comet surface to finally come at rest one km away from its target site. Nevertheless it was operated during the 57 h of its First Science Sequence. The FSS, performed with the two batteries, should have been followed by the Long Term Science Sequence but Philae was in a place not well illuminated and fell into hibernation. Yet, thanks to reducing distance to the Sun and to seasonal effect, it woke up at end of April and on 13th of June it contacted Rosetta again. To achieve this successful landing, an intense preparation work had been carried out mainly between August and November 2014 to select the targeted landing site and define the final landing trajectory. After the landing, the data collected during on-comet operations have been used to assess the final position and orientation of Philae, and to prepare the wake-up. This paper addresses the Flight Dynamics studies done in the scope of this landing preparation from Lander side, in close cooperation with the team at ESA, responsible for Rosetta, as well as for the reconstruction of the bouncing trajectory and orientation of the Lander after touchdown.

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

“…A very stringent plan to coordinate the reception of data obtained from the Orbiter since arrival at the comet, analysis and interpretation of these data, led to a landing site selection process carried out in three steps leading to the required preparations for the actual SeparationLanding-Descent (SDL) sequence [2,12].…”

The near-nucleus gas coma of comet 67P/Churyumov-Gerasimenko prior to the descent of the surface lander PHILAE

“…In the present work we present in detail our own model and the results of its adjustment to the in situ measurements. We restrict ourselves to the so-called "prelanding data" collected in August-November 2014, which we had to interpret in real time to predict the aerodynamic force exerted on the lander during its descent (Jurado et al 2016). We use both fluid and kinetic methods alternately in order to reduce computational expenses but keep the physical accuracy.…”

MASCOT landing on Asteroid Ryugu : flight dynamics team contribution to the landing site selection process

“…The CNES-Mission Analysis (CNES-MA) team is composed of 4 engineers located at Toulouse (France). CNES was already responsible for flight dynamics data for the PHILAE landing (Rosetta/mission) in 2014 [6]. Most of the tools and procedures used for MASCOT are inherited from the PHILAE mission.…”