November 2016 Astronautics

Rosetta - an eventful cruise phase

Rosetta flying over Mars (taken from Philae’s Civa camera).
Rosetta flying over Mars (taken from Philae’s Civa camera).
Paolo Ferri Head of Mission Operations

Paolo Ferri continues his unique insider’s view of this ground-breaking mission and its development from concept through to fruition. In the third in his series of four exclusive articles for ROOM, he recalls challenging and unexpected events during the cruise phase, which included Mars and Earth swing-by’s, and two spectacular asteroid fly-by’s.

The cruise towards Mars was the first opportunity to reduce the frequency of our contacts with Rosetta. We decided to go down to one contact per week and gain experience with that before pushing to longer periods. The spacecraft designers had invented a special attitude control mode for the quiet cruise phase, to save lifetime of some onboard units. This mode also restricted most of the operations on the spacecraft, allowing the ground teams also to relax and recover from the intensive efforts of the past years.

However, in summer 2005, two independent events woke us up from the dreams of a quiet cruise: first, at the beginning of August a temporary problem with an onboard thruster occurred, causing an anomalous change in Rosetta’s velocity and triggering concerns on the health of the spacecraft..

One month later, in early September, the Sun decided to frighten us, blinding the Rosetta Star Trackers by flooding them with charged particles from a large coronal mass ejection event. Both problems occurred when Rosetta was out of radio contact, and we just about managed to quickly recover back to a nominal situation.

These alarming events indicated to us that it was better to abandon our plans just to contact the spacecraft on a monthly basis. We therefore implemented additional software checks onboard and decided that throughout the cruise we would contact the spacecraft at least once a week, to avoid further unpleasant surprises.

Find out more about Rosetta's cruise phase in this exclusive ROOM article, available now to our subscribers.

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