“If everything had gone according to a carefully constructed plan, the European Space Agency’s Philae spacecraft would have descended from mother ship Rosetta, dropped onto its flat, wide-open landing site on Comet 67P/Churymov-Gerasimenko, relayed a rush of findings about the comet’s structure and composition, and then basked in enough sunlight to continue operating for several weeks.
Troubles began when Wednesday when the lander made a pinpoint landing on Agilkia, the Sun-drenched landing site on the “head” of the twin-lobed comet. But two systems designed to anchor the craft in the ultra-low gravity — a downward-pushing thruster and two harpoons — both failed. As a result, Philae bounced not once but twice, coming to rest hundreds of meters from its intended location.
But when Rosetta returned to view, radio contact resumed at 22:19 UT. Still alive, Philae immediately started relaying findings from all 10 of its instruments. Back on Earth, engineers watched helplessly as the battery voltage plummeted. The final measurements came from Ptolemy, an instrument designed to measure ratios of atomic isotopes. After 75 minutes, the transmission ended as Philae slipped into electronic hibernation.
Initial images returned to Earth showed the lander wedged in rugged terrain and deep in shadow from a nearby cliff, its legs angled awkwardly and canted some 30° from horizontal. And yet, the lander was undamaged by by this roller-coaster arrival, ending up with its radio antenna pointed skyward.
Back on Earth, the mission team worked frantically to send up new commands that would salvage as many of the scientific objectives as possible. The drama intensified the morning of November 14th when a communication session with Rosetta ended at 9:58 Universal Time, just as the drill was being deployed. Some feared the battery would die before contact could be reestablished 12 hour later.
Although the lander operated for nearly 57 hours, short of the hoped-for duration, it managed to return all the results from its final sequence of measurements. There was even enough juice to rotate the lander’s body about 35°, to reposition the solar-cell panels to receive more direct sunlight.
“It has been a huge success,” exulted a weary Stephan Ulamec, lander manager for the German aerospace company DLR, which oversaw Philae’s construction. “Despite the unplanned series of three touchdowns, all of our instruments could be operated and now it’s time to see what we’ve got.” Credit: Kelly Beatty