Some problems for the Rosetta space probe in its second close encounter with the comet 67P/Churyumov–Gerasimenko

Four image montage of pictures of the comet 67P/Churyumov–Gerasimenko taken by the space probe Rosetta (Image ESA/Rosetta/NAVCAM)
Four image montage of pictures of the comet 67P/Churyumov–Gerasimenko taken by the space probe Rosetta (Image ESA/Rosetta/NAVCAM)

During the past weekend, ESA’s space probe Rosetta has taken a new flyby about 14 kilometers (about 8.6 miles) away from the comet 67P/Churyumov-Gerasimenko. This means that it hasn’t come as close as in February, however, the comet’s increasing activity caused some problems in Rosetta. Among the consequences, it had serious difficulties in communicating with ESA’s mission control.

The sublimation of ice contained in the comet 67P/Churyumov-Gerasimenko is increasing while it’s coming closer to the Sun. From the scientific point of view, this activity is extremely interesting but in recent days it also proved even a snare for the space probe Rosetta.

Approaching the surface of the comet 67P/Churyumov-Gerasimenko, Rosetta had to fly in the midst of gas and dust. This implies a certain drag effect, which is felt particularly on its solar panels. The main problem, however, was felt on his star trackers, the devices used by the probe to navigate recognizing the patterns of the stars in the sky.

Star trackers are also used to control the Rosetta space probe’s attitude through an function of automatic recognition of star patterns. This is also useful to maintain the orientation of its antenna towards the Earth to send and receive signals from ground stations.

During the flyby of the end of March, the star trackers started having trouble locking on to the stars positions. The gas and dust emitted by the comet 67P/Churyumov-Gerasimenko produced a kind of background noise causing the appearance of hundreds of “false stars” that confused the system for many hours.

attitude errors led to orienting the antenna of the space probe Rosetta incorrectly, causing great communication difficulties. The problems were so bad that the on-board computer entered the so-called “safe mode”, which happens when a spacecraft encounters anomalous flight parameters it can’t correct so it ceases the use of its instruments to avoid the risk of damaging them.

Between Sunday and Monday, Rosetta mission’s team managed to regain communications with the spacecraft and to restore its proper working condition. This also allowed to receive the data collected by its instruments, including photographs taken by its NAVCAM.

Some problems with the space probe Rosetta’s star trackers were already experienced in the February flyby but not severely, so there were no consequences. It’s clear that the increased activity of the comet 67P/Churyumov-Gerasimenko influenced their operation heavily.

During the “safe mode”, the space probe Rosetta moved away from the comet 67P/Churyumov-Gerasimenko and yesterday a maneuver was successfully performed to change its trajectory in order to approach it again. Meanwhile, the mission team is at work to assess how to proceed in the next steps to move forward with scientific research limiting at the same time the risks for Rosetta.

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