Astrometric observations of Phobos with the SRC on Mars Express

New data and comparison of different measurement techniques^⋆

¹ Department of Geodesy and Geoinformation Science, Technische Universität Berlin, Strasse des 17.Juni 135, 10623 Berlin, Germany
e-mail: andreas.pasewaldt@tu-berlin.de
² Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489 Berlin, Germany
³ MIIGAiK Extraterrestrial Laboratory, Moscow State University for Geodesy and Cartography, Gorokhovsky pereulok 4, 105064 Moscow, Russia
⁴ Institute of Geological Sciences, Freie Universität Berlin, Malteserstr. 74-100, 12249 Berlin, Germany
⁵ European Space Astronomy Centre, European Space Agency, Villanueva de la Cañada, 28691 Madrid, Spain

Received: 24 February 2015
Accepted: 25 April 2015

Abstract

Aims. From April 2008 to August 2011 Mars Express carried out 74 Phobos flybys at distances between 669 and 5579 km. Images taken with the Super Resolution Channel (SRC) were used to determine the spacecraft-centered right ascension and declination of this Martian moon.

Methods. Image positions of Phobos were measured using the limb-fit and control-point measurement techniques. Camera pointing and pointing drift were controlled by means of background star observations that were compared to corresponding positions from reference catalogs. Blurred and noisy images were restored by applying an image-based point spread function in a Richardson-Lucy deconvolution.

Results. Here, we report on a set of 158 Phobos astrometric observations with estimated accuracies between 0.224 and 3.405 km circular w.r.t. the line of sight to the satellite. Control point measurements yield slightly more accurate results than the limb fit ones. Our observations are in good agreement with the current Phobos ephemerides by the Jet Propulsion Laboratory (JPL) and the Royal Observatory of Belgium (ROB) with mean offsets of up to 335 m. Our data can be used for the maintenance and update of these models.