MEX Science Data - From the Instrument to the PI
Roberto Porta, Martin Shaw, Michel Denis, Alan Moorhouse · SpaceOps 2006 Conference · 2006
On June 2 nd 2003 Mars Express was launched from Baikonur and placed into its interplanetary trajectory to the Red Planet. The orbiter successfully entered Martian orbit 6 months later on 25 th December. During each orbit, Mars Express spends some time turned towards the planet for instrument observations and some time turned towards Earth for communications with ground stations; it is therefore necessary to find a good compromise in time-sharing between scientific observation and data relay to ground, since concurrent observation and data return to Earth are impossible. To deal with this peculiarity of the Mars Express mission, Industry, Project and the ESOC flight control team have had to study a new engineering solution that implements on-board storage of a large amount of data and its periodic daily downlink to Earth. Data collected by the orbiter instruments are transmitted to Earth at a rate between 28 to 180 kbps. Very variable amounts of scientific data are produced by the scientific instruments on board. These are stored temporarily on the Solid State Mass Memory recording device, and then downlinked from the spacecraft to Earth. From the ground station they are sent, via a ground line, to the European Space Operations Centre (ESOC) in Darmstadt, Germany, and stored in a dedicated Mars Express science data archive from which they are available to the various Principal Investigator teams. This paper will describe the data journey through a very complex communication chain. Mars exploration poses significant new challenges: most particularly the return of such a large data volumes from high-resolution surface instruments over limited telemetry bitrates. In this paper, the problems encountered on Mars Express with regard to data return are analyzed, and the derived solutions are examined.