Attitude reconstruction of MASCOT lander during its descent and stay on asteroid (162173) Ryugu

Abstract Hayabusa-2, a JAXA mission, reached C-type asteroid (162173) Ryugu in June 2018. Hayabusa2 carried MASCOT ( Ho et al., 2016 ), a small lander developed by DLR and CNES. The goal of MASCOT was to perform in situ measurements on the surface of the asteroid by means of its four scientific instruments, substantially contributing in this way to the overall scientific return of Hayabusa2 mission. MASCOT landing occurred the 3rd of October 2018. After its release by Hayabusa2 spacecraft, the MASCOT lander experienced 17 minutes of descent and bounces. Then after stabilization it collected measurements during 17 hours, visiting three slightly different sites. A comprehensive knowledge of MASCOT’s attitudes on the various moment of its mission is essential for the understanding of the science data gathered by the scout. CNES flight dynamics team was involved in the reconstruction of MASCOT landing trajectory and attitude. This paper presents the attitude reconstruction of MASCOT during its descent and on its second landing site. The reconstruction used as inputs the housekeeping data generated by the 6 Photo Electric Cells of MASCOT, as well as the images acquired by Hayabusa2 ONC camera and the MASCAM camera. The assessment was very complex but we determined the attitude with a mean accuracy around 10 degrees during descent and 8 degrees when MASCOT was stable once the second landing site was successfully reached. Nevertheless, for the other phases - bounces, first landing site and last landing site- the lander attitude is still undetermined.