Sunday, November 16, 2014 It began with a bumpy landing and ended with a touching tweet. “I’m feeling a bit tired, did you get all my data? I might take a nap …” tweeted @Philae2014. It was early Saturday morning, and after 57 hours performing science experiments on the surface of comet 67P/Churyumov-Gerasimenko the audacious Philae mission was coming to an end. Not enough light was hitting its solar panels and the spacecraft was preparing to hibernate but, in true Hollywood style, Philae heroically managed to send back all of its data just before the curtain fell. Contact was lost at 00:36 GMT, a few minutes before the scheduled end of the communications window. Within the last blocks of data that Philae returned were readings from an instrument called Cosac. They could reveal the molecular ingredients that became life on Earth, since comets are remnants from the formation of the planets 4.6 billion years ago. Their icy bodies preserve the primordial organic molecules that were incorporated into the Earth and led to the origin of life. “The data collected by Philae and Rosetta is set to make this mission a game-changer in cometary science,” said Matt Taylor, ESA’s Rosetta project scientist. Although now in deep hibernation, there is still a chance that Philae could revive. The comet is currently beyond Mars, but 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, we might have enough solar illumination to wake up the lander and re-establish communication,” said Stephan Ulamec, Philae lander manager at the DLR German Aerospace Centre. In the meantime, the science teams are beginning to analyse the data sent back by the pioneering spacecraft. The first results are expected to be presented at the American Geophysical Union conference in San Francisco next month. The Rosetta orbiter mission will continue for another 20 months, studying the comet and listening for Philae to wake up. It was a week of high anxiety and exhilaration for the scientists involved. Philae touched down on Wednesday afternoon after a seven-hour descent from the Rosetta orbiter. Earlier in the day, engineers had realised that the thruster system on Philae was not responding. The thruster was designed to hold Philae to the surface of the comet as harpoons were fired to anchor it to the ground. Without it, the landing would be much riskier. More bad news was to come. At the moment of touchdown, the harpoon system did not fire. For a while, it looked as if Philae was stable and celebrations began at the European Space Operations Centre in Darmstadt, Germany. But at the lander control centre in Cologne, they were seeing a different story. Magnetic data was showing that Philae was still on the move. They watched with their hearts in their mouths as Philae rebounded from the surface. In the weak gravity of the comet, the spacecraft’s bounce took nearly two hours to complete. It fell back to the comet and bounced a second time – though for just six minutes. Finally, the lander came to rest just before the communications window closed for the night. So pictures had to wait. When images arrived next morning, there was initial confusion. Designed to show a 360° panorama of the landscape and horizon, some showed wall-to-wall rock, others showed open space with stars. Philae had come to rest on its side, wedged between boulders and a rockface. Two legs were in contact with the ground, but one was sticking clear up into space, rather like a car that has skidded into a ditch. “We are exactly below a cliff, so we are in a shadow permanently,” said Jean-Pierre Bibring, Philae’s lead scientist at the Institut d’Astrophysique Spatiale, Université Paris Sud in France. This turned the mission into a race against time. Stuck in the shadows, there was not enough light to recharge the secondary batteries. Everything had to be completed within the 60-hour lifetime of the primary battery. This challenge was always planned for, but the peculiar orientation of the lander meant that compromises had to be made. Engineers began to rework the science plan, while others worked on options for moving Philae into a more favourable position. “We juggled everything so that every instrument got to do a measurement, so we are very happy with the mission so far,” says Valentina Lommatsch, from DLR’s lander team. Meanwhile, from orbit, Rosetta was trying to locate Philae. Data from the radar system pointed to a final resting place about 1km away from the initial touchdown, in a rugged landscape near the wall of a large depression. But images from a camera on Rosetta have yet to see the lander. Strategies for moving Philae included flexing the landing gear to try to make it “hop” out into the sunlight, or spinning up the flywheel, to try to make it cartwheel out. In the event, the engineers ran out of time, but they did succeed in rotating the body so that a larger solar panel was pointing towards the single shaft of sunlight that was reaching the lander. “At the end of this amazing rollercoaster week, we look back on a successful first-ever soft landing on a comet,” said Fred Jansen, ESA’s Rosetta mission manager. “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.”
Posted on: Sun, 16 Nov 2014 15:57:02 +0000
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