Rosetta the comet-chasing spacecraft wakes up

After its three-year slumber, the probe is ready to chase down a comet and place a robot on its surface

By Stuart Clark in Darmstadt and Ian Sample  /  The Guardian, LONDON

Sat, Jan 25, 2014 - Page 9

There was a moment of silence, and then the room erupted. Two hundred scientists, engineers and journalists threw their arms in the air, cheered and bear-hugged their nearest neighbors, whether they knew them or not.

Many had waited a decade for this. In 2004, the European Space Agency (ESA) launched the Rosetta probe on an audacious mission to chase down a comet and place a robot on its surface.

For nearly three years, Rosetta had been hurtling through space in a state of hibernation. On Jan. 20, it awoke.

The radio signal from Rosetta came from 800 million kilometers away, a distance made hardly more conceivable by its proximity to Jupiter. The signal appeared on a computer screen as a tremulous green spike, but it meant the world — perhaps the solar system — to the scientists and engineers gathered at the European Space Operations Centre in Darmstadt, Germany.

At a time when every spacecraft worth its salt has a Twitter account, the inevitable message followed from @Esa_Rosetta. It was brief and joyful: “Hello, world!”

Speaking to the crowd at Darmstadt, Rosetta mission project scientist Matt Taylor said: “Now it’s up to us to do the work we’ve promised to do.”

Just 10 minutes before, he had been facing an uncertain future career. If the spacecraft had not woken up, there would have been no science to do, and the role of project scientist would have been redundant.

The comet hunter had been woken by an internal alarm clock at 10am UK time, but only after several hours of warming up its instruments and orienting toward Earth could it send a message home.

In the event, the missive was late. Taylor had been hiding his nerves well, even joking about the wait on Twitter, but when the clock passed 7pm Central European Time, making the signal at least 15 minutes late, the mood changed. ESA scientists and engineers started rocking on their heels, clutching their arms around themselves and stopping the banter that had helped pass the time. Taylor sat down and seemed to withdraw.

Then there was a flood of relief when the blip on the graph appeared. “I told you it would work,” Taylor said with a grin.

The successful rousing of the distant probe marks a crucial milestone in a mission that is more spectacular and ambitious than any the European Space Agency has conceived.

The 1 billion euro (US$1.4 billion) car-sized spacecraft will now close in on a comet, orbit around it and send down a lander called Philae, the first time such a feat has been attempted.

The comet, 67P/Churyumov-Gerasimenko, is 4km wide, or roughly the size of Mont Blanc. That is big enough to study, but too measly to have a gravitational field strong enough to hold the lander in place. Instead, the box of sensors on legs will latch on to the comet by firing an explosive harpoon the moment it lands, and twisting ice screws into its surface.

Rosetta and Philae will work together to photograph, prod and poke the comet as it hares towards the sun and loops back out to the deepest reaches of the solar system. The comet is quiet now, but as it nears the sun it will start to erupt with plumes of gas and dust and develop a tail that could stretch for more than 1 million kilometers.

“With Rosetta, we will track the evolution of a comet on a daily basis for over a year, giving us a unique insight into a comet’s behavior and ultimately helping us to decipher their role in the formation of the solar system,” Taylor said.

Now that Rosetta has woken up, mission controllers can beam the probe a series of commands to ensure that subsystems and 21 scientific instruments aboard the spacecraft and Philae are in working order. Once they are happy that Rosetta has emerged from hibernation in good health, they can fire the spacecraft’s thrusters to close the gap of 9 million kilometers that separate machine and comet.

The mission ahead promises a spectacular demonstration of relative motion that could only be improved by the accompaniment of The Blue Danube.

The comet is traveling at 60,000 kilometers per hour relative to the sun, but Rosetta will close up from behind at walking pace. Alas, in space, no one can hear Strauss.

“It’s like driving on the M25 when the traffic is moving,” Taylor said. “You are shooting along, but the car overtaking will come past you ever so slowly.”

Rosetta is expected to send back its first images of the comet in May when it is still 2 million kilometers behind. At the end of May, mission controllers will send up commands for a major maneuver that will line Rosetta up for a rendezvous with the comet in August.

Once Rosetta has reached the comet, the probe will begin to scan the surface for a suitable place to drop its lander.

On Nov. 11, mission controllers aim to give the spacecraft the all clear to drop off the 100kg lander.

The lander is expected to take one or two hours to reach the comet, another move that will play out at walking pace as the comet, Rosetta and Philae all hurtle towards the sun at around 16km per second. Rosetta must get into an orbit that minimizes any sideways movement for the lander relative to the comet, so it does not tumble or slide when it lands.

If Philae touches down safely, it will beam back a panorama of its extraordinary environment, along with high resolution images of the face of the comet.

Though Philae is expected to die when its electronics overheat from use, the lander may hold fast to the comet and ride it around the sun for three laps before enough material breaks off to dislodge its harpoon.

“We will face many challenges this year as we explore the unknown territory of comet 67P/Churyumov-Gerasimenko, and I’m sure there will be plenty of surprises, but today we are just extremely happy to be back on speaking terms with our spacecraft,” Taylor said.