New astrometric observations of Deimos with the SRC on Mars Express^⋆

¹ German Aerospace Center, Institute of Planetary Research, Planetary Geodesy, Rutherfordstrasse 2, 12489 Berlin, Germany
e-mail: andreas.pasewaldt@dlr.de
² Technische Universität Berlin, Institute for Geodesy and Geoinformation Science, Planetary Geodesy, Strasse des 17. Juni 135, 10623 Berlin, Germany
³ Moscow State University for Geodesy and Cartography, Extraterrestrial Laboratory, 4, Gorokchovsky pereulok, 105064, Moscow, Russia

Received: 7 December 2011
Accepted: 22 June 2012

Abstract

Between July 2005 and July 2011 Mars Express performed 50 Deimos approaches. 136 super resolution channel (SRC) images were acquired and used for astrometric (positional) measurements of the small Martian satellite. For this study, we have developed a new technique, in which the center-of-figure of the odd-shaped Deimos is determined by fitting the predicted to the observed satellite limb. The prediction of the limb was made based on the moon’s known shape model. The camera pointing was verified and corrected for by means of background star observations. We obtained a set of spacecraft-centered Deimos coordinates with accuracies between 0.6 and 3.6 km (1σ). Comparisons with current orbit models indicate that Deimos is ahead of or falling behind its predicted position along its track by as much as +3.4 km or  −4.7 km, respectively, depending on the chosen model. Our data may be used to improve the orbit models of the satellite.