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Philae on course for landing despite thruster snag

Paul Sutherland, Feature writer
Nov 12, 2014, 18:26 UTC, Updated Nov 12, 2014, 22:52 UTC

Sen—Mission Control, Darmstadt, Germany—The European Space Agency’s daring mission to land the first-ever probe on a comet was on course early today, when Philae was successfully released from mothership Rosetta.

Misison controllers gave the Go for separation despite a technical problem that has arisen with part of Philae’s landing gear. Overnight a gas thruster on Philae was found not to be working. It was meant to help push the comet down to the surface to help avoid a recoil as the harpoons fire. 

The piggy-back craft, which is the size of a washing machine, separated from Rosetta at 8.35 UT. But it took 28 minutes and 20 seconds for mission control to receive the signal saying it had happened.

Now they are having to wait another seven hours for Philae to approach Comet 67P/Churyumov-Gerasimenko, 516 million km (320 million miles) from Earth, and make its landing attempt. 

Gravity is so weak at the comet that there is a danger that Philae could just bounce off. So it will fire harpoons to help latch itself to the landing site and haul itself in. Then its landing legs will screw themselves into the comet, a crumbly surface of rock and ice.

Stephan Ulamec, Philae’s Lander Manager, said: “The cold gas thruster on top of the lander does not appear to be working so we will have to rely fully on the harpoons at touchdown. We’ll need some luck not to land on a boulder or a steep slope.”

Rosetta, which has spent ten years in space chasing the comet, rendezvoused with it in August and found it was shaped like a plastic duck. Its irregular shape as it spins makes landing very tricky. 

But the European Space Agency picked a relatively flat region on the head of the 4.5 mile long comet, and named the site Agilkia.

Speaking today at mission control, Rosetta’s chief scientist is Dr Matt Taylor said:  “Rosetta is the sexiest mission there has ever been. I say she is sexy - but she is not easy.”

Comets excite scientists because they are packed with water and organic materials and so could have delivered the seeds of life to the Earth.

But in a surprise twist yesterday, it was revealed that the comet is “singing”. Instruments studying electrically charged gas, called plasma, from the comet have found it is emitting sounds that they are finding hard to explain.

They are at too low frequencies for the human ear to hear them normally. To make them audible, the team increased the frequencies by a factor of about 10,000 times and heard a strange melody.

They believe the magnetic field around the comet is responsible. ESA scientist Karl-Heinz Glassmeier said: “This is exciting because it is completely new to us. We did not expect this and we are still working to understand it.”

There were a suspenseful few minutes around 11am UT today as mission control waited for Philae to “phone home”. Then the message came, confirming that it was communicating with Rosetta and would be able to report back during its descent.

It was vital that Rosetta and Philae were talking together, because the mothership will relay all its communications and data back to Earth.

Later a photo, obscured by the glare of sunlight, was received from Philae, looking back at Rosetta. And at 3.50 UT, ESA released a photo taken from Rosetta of Philae disappearing into the distance.

Then there were cheers and hugs in the control room shortly after 4pm UK time when mission control received a message back from Philae saying it had landed on the comet.