Mars Express Status Report - March 2010
08 Apr 2010 16:15
Main events and Activities
On 3 March, Mars Express performed the closest ever flyby of Phobos, the larger of the two Martian moons. The spacecraft passed Phobos at an altitude of about 67 kilometres. The flyby was part of the Phobos flyby campaign, which started on 16 February and concluded on 26 March. The campaign, with a total of twelve flybys, provided a unique opportunity for scientific investigations of the small moon. Near the end of the campaign, on 21 and 22 March, spacecraft manoeuvres changed the Mars Express orbit to its planned final 88:25 resonance. This orbit resonance is more favourable for Mars observations by the optical instruments over the next few years of the mission.
The eighth Mars Express occultation season, which started 20 September 2009, as well as the eighth Mars Express eclipse season, which started 10 November 2009, both are ongoing. Over the course of the reporting period, the eclipse durations decreased from 29 minutes to 16 minutes.
Mission performance has been good, with an average of 1.8 science pointings and 4.7 observations per orbit. There were 107 orbits with pericentre in March, corresponding to MTP-75 and MTP-76.
Phobos flyby campaign
Around the closest flyby on 3 March, the radio science experiment was set up to perform the most detailed measurements of Phobos' gravity field to date. The Mars Express radio signal was followed by the Madrid DSN 70m dish, by Cebreros and by three stations from the Joint Institute for Very Long Baseline Interferometry in Europe (JIVE) network.The Phobos flyby on 3 March was the closest ever at an altitude of about 67 km. The originally planned flyby altitude was 50 km, but there was a slight over-performance by a fraction of a percent on the Phobos approach manoeuvre performed several days before the flyby. Although the over-performance was well within the normal limits of uncertainty for such manoeuvres, it meant the spacecraft would now pass Phobos several seconds later and at an altitude of 60 km. More worryingly Mars Express would also pass behind Phobos as seen from Earth. To avoid this undesired blocking of the line of sight during the radio science experiment around the time of closest approach, minor additional orbital offsets were commanded to the spacecraft within the few days remaining before 3 March. These led to a further increase of 7 km in the flyby altitude. In the end the closest ever flyby went very smooth and the signal for the radio science experiment was not blocked at closest approach, resulting in a unique set of data that will be used to study the moon's gravity and internal mass distribution.
For more details and for first results from the Phobos flyby campaign, see the links in the right-hand menu.
The instruments performed nominally during the reporting period. As part of the routine operations all instruments were operated regularly: ASPERA on 94% of the orbits, HRSC on 22%, MARSIS on 100%, OMEGA on 27%, PFS on 66%, and SPICAM on 100% of the orbits. Also 10 VMC observations were made. Together, for all instruments, 99.2% of the planned observations were executed successfully. The daily amount of returned science data was 1.7 Gbit.
Spacecraft status and performance
Thermal and Power sub-systems
Telemetry, Tracking & Command (TT&C)
Radio science investigations using the spacecraft's radio links took place on average 8 times a week. These investigations are part of the Mars Radio Science experiment (MaRS).
On 8 March a commanding test via low gain antennae (LGAe) was run over New Norcia, and on 30 March the Radio Frequency Distribution Unit (RFDU) switch #3, was tested, concluding the recommissioning of the whole TT&C redundancy.
Ground segment status and performance
Mars Express operations were supported by ground stations from the ESA tracking station network (ESTRACK) and the NASA Deep Space Network (DSN).
The number of tracks was on average 18 per week, with 22 passes completed over New Norcia (ESTRACK), 22 over Cebreros (ESTRACK), 2 over Madrid (DSN), 31 over Goldstone (DSN) and 1 over Canberra (DSN). All of the data available on-board the spacecraft has been received on ground.