ESA's spacecraft lands on comet's surface

The Philae has landed. The European Space Agency’s ambitious attempt to place a spacecraft on the surface of a comet succeeded when a signal arrived at the mission control center at Darmstadt, Germany, just after 5 pm local time (11 am Eastern time). Cheers erupted. “We’re there and Philae is talking to us,” said Stephan Ulamec, the manager for the lander. “We are on the comet.”

The lander, Philae, and its 10 instruments have now begun 64 hours of scientific operations before its batteries drain. Solar panels will then recharge the batteries, allowing intermittent operations over the coming months, about one hour every two days.

The landing culminated a long day as the Rosetta maneuvered to the correct position to let Philae go — moments of celebration interspersed with long, quiet stretches of waiting.

The operation proceeded despite a few small glitches and one potential showstopper problem: an apparent failure of a thruster that was to fire right after touchdown to press the lander against the comet’s surface. A pin was supposed to break a wax seal on the gas tank, but repeated attempts did not appear to succeed.

Without the thruster, the washing machine-size Philae would have to rely on ice screws on its landing legs and a couple of harpoons to keep it attached to the comet. The thruster, which was to shoot a stream of cold nitrogen gas, was intended to counteract not just the possibility of Philae bouncing off the surface but also the upward kick from the firing of the harpoons.

Mission managers decided to proceed, because there was no way to repair it, and there was no benefit to waiting.

Philae detached on schedule, for a seven-hour descent to the surface. There was some worrying a couple of hours later when the lander was about 10 minutes late in re-establishing communications with the Rosetta orbiter.

After that, scientists received photos — a blurry image of Rosetta’s solar array taken by Philae about 50 seconds after separation and then a sharper image by Rosetta of the descending Philae.

“We see the lander going down on the right track,” said Andrea Accomazzo, the flight director.

Then there was more waiting, with amusing updates via the Twitter accounts of Rosetta and Philae.

“Finally! I’m stretching my legs after more than 10 years. Landing gear deployed!” was a tweet from Philae.

The web comic XKCD also provided real-time updates with a comic that updated throughout the landing operation, even mentioning the problem with the nitrogen thruster.

In the comic, Rosetta told Philae that mission control was worried about the thruster, and the lander responded, “"I really hope harpoons work on a comet.”

©2014 The New York Times News Service