“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
Philae Seperates from Rosetta and lands on Comet 67P/C-G!
Separation was confirmed at ESA’s Space Operation Centre, ESOC, in Darmstadt, Germany at 09:03 GMT / 10:03 CET. It takes the radio signals from the transmitter on Rosetta 28 minutes and 20 seconds to reach Earth, so separation actually occurred in space at 08:35 GMT / 09:35 CET.
The descent to the surface of Comet 67P/Churyumov–Gerasimenko will take around seven hours, during which the lander will take measurements of the environment around the comet. It will also take images of the final moments of descent.
The Rosetta mission will orbit 67P/C-G for 17 months and is designed to complete the most detailed study of a comet ever attempted.
The spacecraft consists of two main elements: the Rosetta space probe orbiter, which features 12 instruments, and the Philae robotic lander, with an additional nine instruments.
The Rosetta mission achieved a significant milestone by becoming the first mission to rendezvous with a comet. Rosetta is the first spacecraft to orbit a comet nucleus, and is the first spacecraft to fly alongside a comet as it heads towards the inner Solar System. It will be the first spacecraft to examine at close proximity how a frozen comet is transformed by the warmth of the Sun.
The Rosetta orbiter is the first to dispatch a robotic lander for the first controlled touchdown on a comet nucleus. (Credit: Wiki, ESA)
“This is a big step for human civilization,” said ESA director Jean-Jacques Dordain. “The biggest problem with success is it looks easy.”
“How audacious! How exciting! How unbelievable!” said Dr. Jim Green, Director of the Planetary Science Division at NASA Headquarters.
“According to Stephan Ulamec, Philae Lander Manager, DLR, the lander team believe that Philae may have bounced from the surface and settled again in a slightly different place.
Engineers know that the anchoring harpoons did not fire. It is also known that the communications link to Rosetta failed intermittently in an irregular pattern shortly after the landing but always immediately re-established itself.
However, science data has been received and is currently being processed, but the promised first panorama from the surface has not been released.
Rosetta is now out of touch with Philae as the orbiter has dipped below the horizon of the comet. The link to Philae was lost a little earlier than expected but this is probably because a hill or boulder was in the way of the line of sight.
Right now, Philae should be working through its first automatic sequence of science experiments. Contact will be re-established through Rosetta later tonight, and the data downlinked.
There will also be more telemetry to assist the engineers in understanding the exact sequence of events during the landing.
We will know more tomorrow.” (Credit: S. Clark, J. Kingsland)