The European spacecraft Rosette continues to study comet 67P / Churyumov-Gerasimenko, and the closer it is to the Sun, the more confusion caused by inclement orbital weather arises in the automated navigation systems of the spacecraft.
When the surface of the 67P receives more sunlight, Rosetta sees bursts of gas and dust explosive cosmic activities in the ice core of the comet. Observation is carried out from a distance, but it still covers the close surfaces surrounding the 67P.
The orbital environment inevitably becomes denser when a large amount of gas and dust is ejected from the comet driven by subliming ices and heated by the sun's rays. This predictable effect causes resistance to the large solar panels of the Rosetta. During the close passage of the 67P on Saturday, these problems ultimately forced the mission to go into a safe mode, and the mission’s scientists sought a solution.
During the previous close encounter of the comet on February 14, an unexpected problem arose - the navigation system of the spacecraft experienced difficulties in operation due to debris thrown into space. Rosette's star tracker clock constantly points to Earth, and famous stars and constellations autonomously provide them with a high antenna gain — just as sailors have used stars to navigate oceans throughout history. But an increase in debris in the field of the stellar tracking sensor can lead to an erroneous perception of bright comet pieces as stars, causing the system to point far from the Earth. This inevitably affects the connection with Rosetta.
On Saturday, during the flight of Rosetta, just 6 km from the surface, problems with the star tracker resurfaced.
"Attempts were made to restore tracking, but due to the huge amount of background noise in the comet's core, hundreds of false stars were recorded, and it took about 24 hours to restore tracking," Rosetta's blog reports.
Due to the difficulties of tracking, navigation errors led Rosetta farther and farther from the point of destination. The strength of the radio signal fell, indicating that the spacecraft had repeatedly lost its way.
Fortunately, the system recovered automatically and ESA engineers saw a radio signal showing the movement of Rosetta in the right direction. Due to the periodic crash of the tracker, the flight control center tried to reconfigure the on-board systems in order to smooth the contradictions of navigation in a safe mode.
Safety modes are built into the spacecraft systems to prevent errors or failures in a potentially critical situation. When Rosette switches to safe mode, all functions and tools are turned off, only vital systems remain in working condition. From Sunday to Monday, the mission’s scientists managed to safely return to the ship the desired trajectory, which was 200 km from the core and far from the wreckage causing navigation problems.
But another planned close passage, 67P, raises concerns for the safety of Rosetta, especially since an increase in cometary activity is expected in August (and therefore more debris) when comet 67P / Churyumov-Gerasimenko passes the perihelion (the point of closest approach of its orbit around the Sun).
These recent problems have highlighted how difficult it is to investigate a comet so closely, and raised doubts as to whether it should be so close during the next convergence of Rosetta. But it also shows Rosetta’s amazing and important role in understanding the dynamics of comets and how these ancient blocks of icy matter turned out to be in the inner part of the solar system.