After a 31 month hibernation period, the Europe Space Agency’s Rosetta spacecraft has awakened and sent radio signals indicating that it has reactivated itself: Rosetta Mission Report | Mission Status Center – Spaceflight Now.
Rosetta was launched on an Ariane 5G+ rocket on March 2, 2004. It flew passed asteroids 2867 Steins (in 2008) and 21 Lutetia (in 2010), and then went into hibernation in 2011. It will now pursue its main goal, comet 67P/Churyumov-Gerasimenko. It will rendezvous with the comet in August 2014 and go into orbit around it. It will also put a small lander on the comet.
Here’s a short ESA video about Rosetta waking up from its hibernation period:
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.
Update: Here’s a cute animated depiction of the Rosetta mission: