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Rosetta mission: It took 10 years and 6.4m kilometres to catch up with vast comet ... now mission could end as Philae lander's battery runs out

By Linda Stewart

It took 10 years to travel 6.4 million km in pursuit of a comet - and now it could all be over in two and a half days.

Scientists are trying to extract as much data as possible from the Rosetta mission, with the Philae lander expected to run out of juice today as its battery runs out.

Yesterday it was reported that the European Space Agency was considering trying to spin Philae's flywheel to bounce the probe into a better position where its solar array might get more sunlight.

But Queen's University Belfast astrophysicist, Professor Alan Fitzsimmons, who has been studying the comet for more than 10 years, dismissed the reports, saying Philae's signal is likely to be gone for sure by tea-time today.

On Wednesday Philae became the first spacecraft to touch down on a comet, but its harpoons failed to fire and it bounced twice, ending up in the shadow of a cliff.

Professor Fitzsimmons said the Rosetta mission has been a great success, with all the primary science completed in the two and a half days of operations before the battery was due to run out, adding: "This was always planned for."

He said Philae was never guaranteed to get more than that window of battery power, saying: "All the primary science is being done with the lander and we know the data will follow.

"The flight team in Darmstadt did a beyond belief job. It's incredible what they have managed to do.

"We didn't have the first touchdown on a comet: we had the first three!"

Because of the danger of dislodging the probe from the surface, drilling for samples was delayed for a day while Philae's status was assessed, he said.

"Even then there was other science going on - the subsurface probe deployed successfully, the drilling has deployed successfully and now we're waiting for the data to come back. I'm just disappointed we can't get even more of a bonus out of what we call the extended mission.

"Philae will remain where it is as far as we are concerned, but there is a glimmer of hope," Professor Fitzsimmons said.

"Even though Philae only gets one and a half hours of sunlight to recharge the batteries, the comet is moving closer to the sun and sunlight is becoming more intense, so the amount of power Philae gets every day will be increasing.

"It's also in northern sun at the moment and with the move towards the equinox the sun is more overhead, so at the equinox Philae could get more sunlight.

"So there is a remote possibility of Philae reactivating in a few months' time, but it's a long shot and we shouldn't depend on it."

What the future holds for Philae

1. Battery power was expected to last long enough for last night's data transmission from Philae. ESA may decide to spin Philae's flywheel to bounce the lander into a new position where more sunlight will be available to recharge its batteries.

2. Scientists say 80-90% of the intended science has been carried out, but there is a question mark over whether all the data will be uploaded before the lander loses battery power.

3. All instruments are working well. Scientists were due to find out last night whether drill samples have been taken successfully. There will be more radar data to try to locate Philae.

4. As the comet approaches the sun, there may be enough power from Philae's solar panels to reactivate the lander.

5. Last night, the team were awaiting 84 images of the comet from Rosetta, which will be used to try to locate the lander. Descent and touchdown images were also being relayed.

6. A manoeuvre command has been sent to Rosetta to keep the Philae landing area in sight over the coming days.

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