The European Space Agency (ESA) has given the green light for its unmanned Philae probe to attempt the historic first landing on a comet. At a press conference at at the European Space Operations Centre in Darmstadt, Germany, representatives of ESA and the German Aerospace Centre told the media that both the Rosetta mothership and the Philae lander are in excellent shape for Wednesday morning’s (GMT) planned separation and landing on comet 67P/Churyumov-Gerasimenko.
After years of voyaging that included three flybys of Earth, one of Mars, and a long detour out beyond Jupiter as it built up enough speed to catch up to the comet, the pair of Rosetta and Philae are about to fulfill their primary mission. According to ESA, the commands for separating Philae from Rosetta and then guiding it down for a soft landing on 67P have been uploaded with last minute commands based on Rosetta’s position awaiting final writing and approval before transmission. In the meantime, Rosetta is carrying out an engine burn that will bring the orbiter into the correct position for separation.
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Prior to separation, the Philae lander will be turned on at 18:33 GMT on Tuesday. This will mark the first time that the lander’s systems have been activated since its long hibernation on the way to the comet. The batteries will be warmed to an operational temperature, its stabilizing flywheel started, and its systems checked by mission control via telemetry.
As Rosetta maneuvers and Philae is brought on line, flight engineers will monitor progress and give a series of go/no go decisions as to whether to proceed. If all goes well, Philae will separate from the orbiter at 09:03 GMT on Wednesday with landing at 16:02, with a 40 minute window of variability. Because to the 51 million km (32 million mi) distance from Earth, it takes radio signals 28 minutes and 20 seconds to reach Earth. This delay, plus the fact that rocket maneuvers cause the spacecraft to go in and out of communication with mission control, means that the robot explorers are programmed to operate autonomously.
Once Philae has landed, ESA says that it will take several minutes for it to confirm touchdown until the lander has completed securing itself to the comet using a harpoon due to the extremely low gravity. If successful, Philae will then begin a two and a half day science mission, which could be extended if its solar panels are able to charge its batteries.
The ESA animation below shows Philae's planned separation from Rosetta.