Problems for Rosetta during its most recent fly-by of Comet 67P/C-G


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During its most recent close fly-by of Comet 67P/C-G Rosetta had a number of issues that caused the spacecraft to go into safe mode.

During the most recent flyby, a number of issues were reported, starting with the primary star tracker encountering difficulties in locking on to stars on the way in towards closest approach. Attempts were made to regain tracking capabilities, but there was too much background noise due to activity close to the comet nucleus: hundreds of ‘false stars’ [from comet debris] were registered and it took almost 24 hours before tracking was properly re-established.

In the meantime, a spacecraft attitude error had built up, resulting in the high gain antenna off-pointing from the Earth. Indeed, a significant drop in the radio signal received by ground stations on Earth was registered. Following recovery of the star tracker system, the off-pointing was immediately automatically corrected and the operations team subsequently saw a return to a full strength signal from the spacecraft.

However, issues with false stars were still occurring. Cross comparisons with other navigation mechanisms showed inconsistencies with the star trackers and some on board reconfigurations occurred. While attempting to reconfigure those, the same error occurred again leading this time to an automatic safe mode on Sunday afternoon. Safe modes occur when certain spacecraft parameters fall out of their normal operating ranges and the spacecraft automatically takes measures to preserve its safety. This also includes switching off the science instruments to protect them.

Rosetta is operating nominally now, but these issues are going to get more serious in the coming months, as the comet gets more active. Rosetta’s engineering team is going to have to come up with a method for the spacecraft’s star trackers to distinguish between stars and the debris in the comet’s coma. If they don’t it is likely that they will have to reduce the close fly-bys significantly.

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2 comments

  • BSJ

    What if some of the false stars are now dust specks on the lens…?

  • pzatchok

    I am wondering if they are in someway using the same technique to spot the guide stars that they use to photograph deep space objects?

    They don’t just use one photo but many photos layered on top of each other dropping out all photons that do not register on several frames in the same place. They can program it to use one or hundreds of frames.

    Plus a specific filter might help block out the gasses and dust particles flying off of the comet.

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