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Time to wake up, Rosetta!

Final phase of European space mission gets underway on 20 January 2014

You can never have too many reminders when you’ve got an important appointment. For one European probe, the most important date in its mission is coming up this year. After a ten-year journey, Rosetta will reach its target: comet 67P/Churyumov-Gerasimenko. To ensure it doesn’t miss this crucial rendezvous, Rosetta has four alarm clocks on board that have been set to wake the probe up from deep-space hibernation at the stroke of 10.00 (GMT) on 20 January 2014.

Tommy Strandberg, an engineer at Airbus Defence and Space in Friedrichshafen, is among those who will be eagerly awaiting some sign of life from the remote craft. As Navigation Guidance and Control Manager, he was part of the team at Airbus Defence and Space (formerly Airbus Defence and Space) that launched the mission. “The signal for Rosetta to wake up will be given as soon as at least two of the clocks have counted down to zero,” says Tommy.

On the big screen, this surge in activity on board Rosetta would likely be portrayed with beeping sounds and blinking lights. But in reality, even someone flying alongside the probe wouldn’t be able to see anything happen straight away, as the first priority is to get the spacecraft warmed up. Rosetta’s navigation instruments have to be brought to an operational temperature of 10 to 30 °C. Next comes the damping of the rotations that stabilised the craft’s flight path over the preceding 957 days. Its solar cells will be angled towards the Sun and its parabolic antenna towards the Earth. At long last, Rosetta will once again be able to communicate with Earth. Scientists at the European Space Operations Centre in Darmstadt, Germany, hope that sometime between 16.30 and 17.00 they will receive a signal indicating that after its ten-year flight, Rosetta is ready to enter the home straight.

Tommy and the entire mission team are in for an exciting year – not least because many technologies and processes made ready for this space mission, which launched on 2 March 2004, will be being used for the first time. Never before has a craft powered solely by solar energy dared to penetrate so far into space, for example. At its current distance of around 800 million kilometres from the Sun, Rosetta must make do with just under 4 percent of the sunlight available to satellites in orbit around the Earth. With a total wingspan of 32.7 metres, its solar panels still manage to generate 440 watts of electricity – enough to tackle the final leg of the journey.

According to Tommy’s calculations, Rosetta’s navigation camera could glimpse the mission’s quarry from a distance of 100,000 kilometres by March. After course correction in May, the probe will be set to rendezvous with 67P/Churyumov-Gerasimenko in August, enter into orbit around the comet – which is just a few kilometres across – and accompany it as it heads towards the Sun over the following months.

This is both a pioneering achievement and a journey into the unknown. “Nobody knows exactly how large or sturdy the comet is,” says Tommy. “What we do know is that the comet’s gravitational pull is only around a millionth of that of the Earth. Without frequent course corrections, it would probably be almost impossible to keep Rosetta in orbit.” Barring any complications, the scientists will be able to study the surface of 67P/Churyumov-Gerasimenko over the weeks that follow, keeping an eye out for a suitable place for the Philae lander to put down. Up to now Philae has been along for the ride, waiting for the moment – another first – when it will land on the comet in November.

Designed with an operating life of six months, the lander will carry out tests on the mysterious matter of comets. Scientists hope that the findings will give us an insight into the history of our solar system and the origins of life. But all that time, 67P/Churyumov-Gerasimenko will be getting closer and closer to the Sun and the rising temperatures will cause more and more matter to vaporise, forming the comet’s signature tail. Just how long Philae will be able to withstand this turbulent ride is unclear.

As mother probe on the other hand, Rosetta is set to be with the comet in August as it reaches perihelion and will accompany it on its journey back away from the Sun until the end of 2015. And while Tommy and his fellow space engineers will then be able to relax a little and look back with pride at their part in the most ambitious mission in European space history, astronomers will just be getting started on years of evaluating the collected data. Even after Rosetta has disappeared into the depths of space, the mission will remain as exciting as ever.