Like nervous parents, scientists and engineers at ESA are pacing the floor of mission control as they await word of whether or not the Rosetta spacecraft has survived 31 months of hibernation. The unmanned comet chaser was scheduled to reactivate itself today at 10:00 GMT, but the time required to complete the operation and the distance a radio signal must travel back to Earth means that the space agency will not know until at least 17:30 GMT if the probe is operating again or has become deep space scrap.

Launched in March 2004 atop an Ariane 5 G+ rocket from Kourou, French Guiana, Rosetta is charged with the mission of rendezvousing and orbiting comet 67P/Churyumov-Gerasimenko. That may sound simple, but it required a journey that so far has taken ten years, during which the spacecraft executed a complex orbital ballet with four gravity assists involving three flybys of Earth and one of Mars to build up enough velocity to reach 67P in May of this year. During this time, it also rendezvoused with the asteroids Stein and Lutetia. The only snag in this plan was that the final loop of Rosetta’s orbit sent it out past Mars toward that of Jupiter. This was much too far for the probe’s solar array to keep it powered, so to stop it from freezing to death and keep it stable, mission control set it spinning at a rate of about once per minute, then gave it the order to go into deep hibernation on June 8, 2011. Since then, Rosetta has only been running a few heaters to keep the electronics working.

Thirty-one months later, Rosetta is now 673 million km (418 million mi) of the Sun, which is close enough for the solar array to provide sufficient power. However, it isn’t receiving any signals from Earth. In fact, mission control is waiting for a signal from it.

Rosetta’s computer was programmed to automatically start the wake up sequence at 10:00 GMT. If all is going to plan, the first thing the craft did was to warm up star trackers, which will take about six hours. Then it will use its thrusters to slow its rotation and point its solar array directly at the Sun. The star trackers will then figure out Rosetta’s attitude, the high-gain antenna will point at Earth and a signal will be beamed across 807 million km (501 million mi) to mission control in Darmstadt, Germany; a journey that will take a nerve-wracking 45 minutes.

In the end, ESA says that it hopes to receive the signal today between 17:30 and 18:30 GMT, and the news will be relayed to the world immediately via Twitter. Once contact is reestablished, ESA will carry out system checks and reactivate its suite of experiments as it travels the remaining 9 million km (5.5 million mi) to 67P/Churyumov–Gerasimenko, which it is scheduled to rendezvous with in August after a course correction in May. If all goes well, it will become the first spacecraft to go into orbit around a comet in August.

Artist's concept of the Philae lander (Image: ESA)

Once on station, Rosetta, which is named after the famous stone slab that provided the key to translating Egyptian hieroglyphics, will begin its main mission of studying the origins of comets, the characteristics of the comet nucleus, the physical properties of the gases they emits, and how comets alter as they approach the Sun. In addition, it will deploy its Philae lander to make an historic first controlled landing on a comet’s surface.

The mission is scheduled to end on December 31, 2015, after 67P reaches its closest to the sun on August 13 of that year.

The video below outlines Rosetta’s wake up procedure.

Source: ESA

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