During a 14km flyby of the nucleus of Comet 67P/Churyumov Gerasimenko on 28 March 2015, the valiant ROSETTA spacecraft of the European Space Agency had a major pointing error. As the comet gets closer to the Sun, it is outgassing water vapour and dust, and this was the cause of the error. As ROSETTA headed towards the larger of the two lobes of the dumbbell shaped nucleus it experienced a pointing error which caused the craft to fall into a safe mode. ESA scientists eventually traced the fault to the craft’s star trackers which confused illuminated dust for the stars which the craft gets its navigational “fixes” from. Although ROSETTA did eventually recover its orientation and came out of safe mode, space engineers note that the star trackers are still being confused.
Scientists are anxious to keep ROSETTA in working condition to observe the maximum outgassing as the comet makes its closes “perihelion” approach to the Sun. As it is, it is still hoped that contact can be regained with the stranded PHILAE lander which might be able to use solar illumination to recharge its batteries enough to relay a signal back to Earth via ROSETTA.
ROSETTA has performed an engine burn on 1 April 2015 to move the craft from a 400km altitude to the comet back to 140km.
