Rosetta Status Report - April 2005
The spacecraft was gradually configured for the swing-by, which included e.g. the activation of the fourth reaction wheel on 25 February, switching the RF link from X-band to S-band, and, on 2 March, from the High Gain to the Low Gain antenna. On 1 March the first two instruments of the payload were activated, RPC and PHILAE ROMAP. SREM remained active as usual. On 4 March operations of VIRTIS and MIRO were initiated. PHILAE CIVA was operated for three hours around closest approach to Earth. The OSIRIS Imaging System did not participate in the observations due to some still unresolved problems with the instrument cover.
The Earth swing-by operations included various open-loop tracking tests with the Navigation Cameras, using the Moon as target, on 4 March. All operations were successful, with one exception: a problem in configuration of the link between Camera B and the on-board Mass Memory, preventing pictures taken by this camera to be stored on-board. All images were provided by Camera A.
Closest approach to Earth occurred at 22:09 UTC on 4 March at an altitude of 1954 km. Shortly after, at 01:00 UTC on 5 March the spacecraft was commanded into Asteroid Fly-by mode, using the Navigation Camera pointed to the Moon to control the attitude. This was the first and actually only in-flight test opportunity for this mode, which will be used during the fly-bys of asteroid Steins in 2008 and Lutetia in 2010, respectively. The test lasted 9 hours and was a complete success. The Navigation Camera tracking performance was constantly within less than 0.05° from the estimated direction and the estimated attitude deviation during the test stayed always below 0.1°.
The final off-pointing at exit was of the order of 0.05°. No increase in background in the Camera could be detected towards the end of the test, when the Sun angle reached 45°; no straylight was detected. The spacecraft survived well the radiation belt crossings and the Earth proximity. Only a few SEU counts were reported, the reaction wheels sustained the gravity gradient torques, the Star Tracker immediately acquired patterns after having exited the proton belt. One can summarize that all systems worked nominally.
After the end of the test the spacecraft was pointed back to Earth to allow the payload and the Navigation Cameras to observe the Earth. The spacecraft was reconfigured into nominal mode and by 10 March all generated science data had been transmitted to Earth.
Operations have entered a fairly quiet mode again with the preparation and test of the Near Sun Hibernation mode. The next major event will be the monitoring of the Deep Impact encounter with comet Tempel 1, where a two week payload operations sequence, starting 28 June, has been introduced into the mission timeline.
During a number of the passes payload software upgrades and tests have been performed, most importantly to resolve the OSIRIS front door mechanism anomaly and the ROSINA RTOF operations. For ROSINA RTOF good progress was made, however, the sensor still needs considerable fine-tuning until it can be operated autonomously. However, these tests and software upgrade will only be performed after the second Earth swing-by end of 2007 to make use of the then short round-trip light time. The OSIRIS front door issue hasn't been resolved yet. A working group has been set up with involvement of ESA experts.
The RSOC team has been responsible for preparing all science operations since end of 2004 and the interfaces with the experiment teams and the Rosetta Mission Operations Centre at ESOC worked flawlessly. The first iteration of the Deep Impact science sequences and payload pointings were completed early April.
During the 18th Rosetta Science Working Team meeting at ESOC, 8-9 March, the Rosetta PIs presented preliminary results for their experiments gathered during the Earth swing-by period. Overall the instruments performed very well and very good scientific and calibration data were collected both by the remote sensing and the plasma instruments that were active during that phase. For the first time VIRTIS could verify the science performance and all indications are that the instrument provided excellent results. This positive assessment of the Earth swing-by activities was confirmed by the PHILAE Lander team in presentations at the first Lander Science Workshop, 4-6 April, near Goettingen.