04 Mar 2011 13:56

The trim manoeuvre (ΔV 17.29 ms^-1) of RDVM#1, aborted due to a spacecraft attitude error on 10 February, was performed on 17 February. Detailed orbit determination is being carried out to assess the possible need for a further correction. Shortly before the trim manoeuvre, the performance of the solar arrays at four AU was tested; results were very close to the most recent predictions. These data will now be used to perform a detailed assessment of the operations timeline for the deep space phase.

During the reporting period, mission operations were conducted using the ESA New Norcia (NNO) ground station and the DSS-24 (Goldstone, 34 metres), DSS-25 (Goldstone, 34 metres), DSS-26 (Goldstone, 34 metres) and DSS-55 (Madrid, 34 metres) NASA Deep Space Network (DSN) antennas.

At the end of the reporting period on 18 February, Rosetta was at 556 million kilometres from the Earth (3.71 AU); one-way signal travel time was 1855 seconds (30 minutes 55 seconds). The distance to Sun was 600.86 million kilometres (4.01 AU).

Spacecraft

Attitude and orbit control system
The Reaction Control Subsystem (RCS) is configured with thruster set A as nominal, set B as redundant. The TRIM 1B burn was performed using RCS A and confirmed that no permanent failure is present in this branch. As reported in the previous period, performance of the RCS during reaction wheel offloading (that is, short, sporadic pulses) is not as expected and the problem seems to be with the cold-start thruster model at low pressures. This will be further investigated in view of the need to employ the thrusters during the spin-up manoeuvre required before entry into deep-space hibernation. Performance during ΔV manoeuvres is consistent with the available model. The manoeuvre, which lasted about 29 minutes, was completed around 30 seconds earlier than predicted, indicating a slight over-performance of the thrusters with respect to the model.

The inconsistent attitude and orbit control system behaviour observed during the safe mode on 10 February has been understood and traced to a non-ideal setting of a filter within the attitude controller.

Future Milestones

The remaining payload activities to be completed before hibernation entry are now being planned and will be executed before mid-March to have the spacecraft ready for the opposition phase in April and May.

Summary of upcoming events:

• 3 Mar 2011: TRIM 2 burn (if needed)
• 12 April 2011: Start of opposition phase
• 20 May 2011: End of opposition phase
• 8 June 2011: Hibernation entry

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Legal disclaimer
This report is based on the ESOC mission operations report, WOR #152. Please see the copyright section of the legal disclaimer (linked from the home page http://sci.esa.int) for terms of use.