The First Rosetta Passive Cruise: Approach and Experience

Paper number

IAC-06-A3.5.03

Author

Dr. Paolo Ferri, European Space Agency/ESOC, Germany

Coauthor

Mrs. Elsa Montagnon, European Space Agency/ESOC, Germany

Coauthor

Mr. Jose Morales, European Space Agency/ESOC, Germany

Year

2006

Abstract

The International Rosetta Mission, a cornerstone mission of the European Space Agency Scientific Programme, was launched on 2nd March 2004 on its 10 years journey towards a rendezvous with comet Churyumov-Gerasimenko. Once reached the comet nucleus in summer 2014, Rosetta will orbit it for about 1.5 years down to distances of a few Kilometres and deliver a Lander, named Philae, onto its surface. After the first intense year of flight, in which the spacecraft and payload were commissioned, the first Earth swing-by was carried out and most of the operational modes validated in flight, the spacecraft finally entered its first Passive Cruise phase end of July 2005.

Given the long duration of the mission, the spacecraft was designed to sustain long periods during cruise in which the number of active on-board units and the need for ground contact are minimised. The mission operations baseline was consequently defined such that for all periods between major cruise events like planet swing-bys, asteroid fly-bys or payload checkouts, the spacecraft would be configured in a hibernation mode, and the frequency of ground contacts reduced to once per month. Advantages of such approach are the increase in reliability of on-board units, in particular the reaction wheels and the gyroscopes. Also a cost reduction could be achieved in the mission operations during cruise, with the reduction of ground station and control centre resources utilisation. The disadvantages are clearly a reduced visibility from ground on the status and performance of the spacecraft, and the impossibility of a rapid intervention in case of anomalies developing on-board.

The experience of the first year of passive cruise and some important events occurred during this period have lead to a revision of the overall approach. The frequency of contact passes is now kept to typically once per week, mainly driven by the need to retrieve the full history of housekeeping telemetry generated and stored during the non-coverage period. This frequency of contacts represents the highest one that can be achieved without impacting significantly on the available ground station and manpower resources. A side effect of this approach has been the increased availability of the spacecraft for troubleshooting and in-flight testing, and for previously unplanned payload operations. This has in turn increased the workload on the small flight control team, which was already constantly occupied with medium and long term planning activities for the future critical mission phases, anomalies investigation and related on-board software changes development, testing, validation and implementation.

This paper describes the original concept defined for Rosetta to sustain the long passive cruise to the comet, and its justification in terms of cost and reliability. The experiences of the first year are described, and the changes in the approach introduced following the in-flight experience are detailed. The rules defined for the future passive cruise phases of Rosetta, and generic lessons and recommendations for missions with similar long cruise and hibernation approach are derived.

Abstract document

IAC-06-A3.5.03.pdf

Manuscript document

IAC-06-A3.5.03.pdf (🔒 authorized access only).

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