Philae lander goes to "sleep" after batteries die

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Artist's impression of the Philae lander (Image: ESA) (Image: ESA)

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After its historic landing on a comet, the Philae spacecraft has gone silent. Trapped on its side in a shadowed hole, the unmanned European Space Agency (ESA) lander was unable to receive enough sunlight to recharge its battery and contact was lost today at 00:36 GMT when power levels dropped below critical.

On Wednesday, the washing machine-sized lander made a freefall descent from the Rosetta mothership to the surface of comet 67P/Churyumov-Gerasimenko. Unfortunately, the thruster designed to press it down on the comet and the harpoons to anchor it failed to operate and Philae bounced back into space. After bouncing a second time, it turned on its side and came to rest in a hole or crevice about a kilometer from the original landing site.

In this new position, some of the solar panels that charge the lander’s batteries were buried and the rest only received about 1.5 hours of sunlight per day, which was not sufficient to maintain the systems and keep the spacecraft warm.

Battery readout from Philae's final hours (Image: ESA)

While engineers worked to find a possible solution to the problem, the Philae science team ordered the lander to activate as many of its experiments as it could and placed priority on returning as much data as possible via the Rosetta mothership. According to ESA, Philae was still able to carry out most of its planned first science sequence experiments and transmit the data back to Earth. In addition, telemetry confirmed that Philae successfully carried out the first ever drilling operation on a comet.

Due to the 60-hour window available before power was lost, the engineers had very limited options for rescuing the trapped spacecraft. They decided against trying to deploy the harpoons for fear of pushing the lander off the comet or damaging it, but about three hour previous to the shutdown, mission control in Darmstadt, Germany ordered the lander to rotate its main body 35 degrees to expose a larger solar panel. The maneuver proved successful, but it was too little too late.

Image taken of comet 67/P by Philae during its descent (Image: ESA)

ESA says that Philae is now in “idle mode,” where all the scientific experiments and most of the systems are shut down. Contact could still be re-established if enough sunlight falls on the spacecraft, but this is extremely unlikely. However, the Rosetta orbiter has been programmed to listen for a signal on its next pass over the landing site at 10:00 GMT on Saturday.

"Prior to falling silent, the lander was able to transmit all science data gathered during the First Science Sequence," says DLR's Stephan Ulamec, Lander manager. "This machine performed magnificently under tough conditions, and we can be fully proud of the incredible scientific success Philae has delivered."

Source: ESA

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