Rosetta: Alarm to sound for comet mission

One of the most daring space missions ever undertaken reaches a key milestone on Monday. Europe’s Rosetta probe was launched a decade ago on a long quest to chase down and land on a comet, and has spent the past two-and-half-years in hibernation to try to conserve power.
But at 10:00 GMT, an onboard "alarm clock" is expected to rouse the spacecraft from its slumber. Rosetta will then warm its systems before sending a signal to Earth. Receipt of this "I’m awake" message will confirm the great endeavour is still on course.
Rosetta is due to rendezvous with Comet 67P/Churyumov-Gerasimenko in August. And after spending a couple of months studying and mapping this 4km-wide ball of ice and dust, it will drop a small robot on to the comet’s surface to gather samples and panoramic pictures.
Controllers at the European Space Agency’s (Esa) operations centre here in Darmstadt, Germany, do not know precisely when Monday’s all-important message will arrive, but they anticipate receiving it sometime between 17:30 and 18:30 GMT.
Before it can send the signal, Rosetta must work through a sequence of activities that will last several hours.
First, it must raise the temperature of the sensor chips in its navigation instruments, then it must stop the stabilising spin into which it was placed for hibernation, and finally it must find Earth on the sky and point its main antenna in that direction.
"It will be transmitting just the ‘carrier signal’, so at that point there’s no data coming down from the spacecraft," explained Andrea Accomazzo, Rosetta’s operations manager.
"We just receive a firm frequency. In theory, it would be like a continuous beep if you were to convert it into sound. We will see it on a screen that is basically a spectrum analyser.