Comet probe sends data to Earth, then goes to sleep

Racing to stay alive after a bouncy double landing that left it in the shadows, the Philae comet probe performed some technical gymnastics Friday to reposition itself to get more sunlight and transmit a trove of data before its batteries died.

As mission control nervously waited for confirmation that the maneuvers had succeeded, scientists got some good news: Philae began sending data back to Earth after re-establishing its radio link with the Rosetta orbiter.

About 7:45 p.m. ET, the European Space Agency reported it had lost the signal and had no more communication with the lander, which had switched to standby because of low power and had turned off its instruments. But all scientific data from the first sequence had been transmitted successfully before the little lander went to sleep.

"I'm feeling a bit tired, did you get all my data? I might take a nap…," it tweeted.

"You've done a great job Philae, something no spacecraft has ever done before," the agency replied.

On Saturday, scientists were listening for Philae's signals, but they believe it is unlikely that communication will be restablished soon, said ESA's head of mission operations, Paolo Ferri.

"We don't know if the charge will ever be high enough to operate the lander again," Ferri told The Associated Press. "It is highly unlikely that we will establish any kind of communication any time soon, but nevertheless the orbiter will continue to listen for possible signals."

They were scheduled to check for communications at 5 a.m. ET, he said.

At about 6 p.m. ET Friday, the probe's body executed a 10-minute "lift & turn" on its landing gear, the ESA said. Philae reported that its 35-degree rotation was successful.

"Looks like a whole new comet from this angle :)," the probe tweeted from outer space.

But about 35 minutes later, the lander said it was "running out of energy quite fast now" and "getting tired," with its battery voltage "approaching the limit soon now."

After a 10-year voyage, Philae was dropped by Rosetta and landed Wednesday at 41,000 mph on the comet, named 67P/Churyumov-Gerasimenko. It touched downas planned on a sunny plateau, but harpoons fired to secure the craft failed, and the lander bounced more than a half-mile into space. Two hours later it fell back, tumbled and came to rest at an awkward angle in the shadow of a cliff or big rock.

Philae has been receiving just 1.5 hours of sunlight instead of the expected 6-7 hours. This is not enough to charge the secondary batteries. Initial battery life was estimated at 60 hours, so without sufficient sun on its solar panels, Philae's mission could be over soon.

The lander drilled into the comet for the first time earlier Friday. In addition to the scientific data, controllers were hoping it might help nudge the probe nearer to a sunny patch.

When the radio link with the orbiter was re-established, controllers were relieved to learn that the drilling caused no major disruptions, and that the instrument that handled the first soil sample was sending data home, 310 million miles away.

"56 hours that I'm on the comet now conducting science measurements non stop!," Philae tweeted proudly.

Contributing: The Associated Press