Visualisation of how the Rosetta spacecraft wakes up from deep space hibernation, 673 million kilometres from the Sun, on 20 January 2014.
Prior to entering hibernation on 8 June 2011, Rosetta was oriented so that its solar arrays faced the Sun, and it began rotating once per minute for stability. The only devices left running were its computer and several heaters.
Rosetta’s computer is programmed to carry out a sequence of events to re-establish contact with the Earth on 20 January, starting with an ‘alarm clock’ at 10:00 GMT. Immediately after, the star trackers begin to warm up. Around 6 hours later the thrusters are fired and the slow rotation stops. A slight adjustment is made to Rosetta’s orientation to ensure that the solar arrays now face the Sun. Then the star trackers switch on to determine its attitude. The spacecraft rotates towards Earth, and the transmitter is switched on. Then Rosetta’s high-gain antenna points to Earth and the signal is sent. The journey takes 45 minutes before the signal is received and mission controllers can begin to check Rosetta’s health, ready for the next phase of the mission.
The first opportunity for receiving a signal on Earth is between 17:30 GMT and 18:30 GMT.