Rosetta mission's Philae lander powers down in comet's darkness

The audacious Rosetta mission’s attempt to land on a comet and send back scientific data is over – for now.

Despite a last-roll-of-the-dice attempt to nudge the Philae lander into better sunlight, which might have recharged its batteries, the end came when contact was lost at 00.36 GMT on Saturday morning.

Engineers had warned earlier in the day that the lander, which is the size of a washing machine, may not have had enough power to make contact at all.

There was still a tense wait at the European Space Agency’s (ESA)operations centre in Darmstadt, Germany, as Philae’s signal was not acquired until 02.19 GMT, more than an hour later than expected, raising hopes that the lander may have moved into a sunnier spot.

Data acquired during the night showed that Philae had moved a tiny bit, but not enough to immediately save the mission.

Scientists hope, however, that the comet Philae now calls home, known as 67P/Churyumov-Gerasimenko, will be close enough to the sun in August 2015 for the stronger sunlight to revive the lander.

By flexing the landing gear on Saturday morning, engineers managed to raise the body by 4cm. They also rotated the body by 35°, hoping that the shaft of sunlight that is reaching the lander would hit one of its larger solar panels.

Soon after contact was made on Friday night, engineers reported that the battery’s voltage was falling fast. The end was close. The signal stopped just before the scheduled end of communications, indicating the mission was over, but the lander returned the last blocks of information just before it died.

“Prior to falling silent, the lander was able to transmit all science data gathered during the first science sequence,” said Stephan Ulamec, the lander manager at the German Space Agency (DLR), which built Philae.

This included data from the COSAC instrument ,which was designed to analyse the chemical composition of the comet’s surface. The information collected could reveal the organic molecules that came to Earth 4.5bn years ago and led to the origin of life.

Philae touched down on Wednesday afternoon after a seven-hour descent from the Rosetta mothership, but the landing did not go smoothly. A harpoon system designed to anchor Philae to the surface did not fire, and the lander rebounded.

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In the weak gravity of the comet, Philae’s bounce took nearly two hours to complete. It then performed a second bounce, this time of just six minutes long before coming to rest. The mission team are still working to determine its precise location, which is thought to be about 1km away from the targeted spot.

Camera images showed that Philae came to rest wedged on its side between boulders and a cliff face. Stuck in the shadows, there was not enough light to recharge its secondary batteries.

The mission became a race against time to collect all the science it was designed to do in the first 60 hours, the lifetime of its primary battery. In reality the battery lasted a little longer. Philae worked for 57 hours on the surface, and 7 hours during its descent.

“At the end of this amazing rollercoaster week, we look back on a successful first ever soft landing on a comet. This was a truly historic moment for ESA and its partners.

“We now look forward to many more months of exciting Rosetta science and possibly a return of Philae from hibernation at some point in time,” said Fred Jansen, ESA’s Rosetta mission manager.

The comet, known as 67P/Churyumov-Gerasimenko, is currently beyond Mars, but its orbit is bringing it closer to the sun. In August 2015, it will be close to Earth’s orbit and the sunlight will be much stronger.

“We still hope that at a later stage of the mission, perhaps when we are nearer to the sun, that we might have enough solar illumination to wake up the lander and re-establish communication, ” says Ulamec.