Friday, March 13, 2015
IN NOVEMBER, A spacecraft made a dramatic, first-ever landing on a comet—three times. After the Philae lander touched down on comet 67P/Churyumov-Gerasimenko, the harpoons that were supposed to latch it onto the surface didn’t fire, and instead, the spacecraft bounced back into space before returning to the comet. Another shorter hop then took it to its current, shady resting spot. Since then, the Philae lander has been slumbering in the cold and dark some 286 million miles away, with only meager recharging from its solar panels. Now, with warmer and brighter days ahead, it’s time to see if the Philae lander is awake and ready to get back to work. Just don’t expect anything too soon.
Today, for the first time since it started napping, mission engineers have begun trying to communicate with Philae, which exhausted its batteries soon after landing. After four months, the orbit of the European Space Agency’s Rosetta spacecraft, which has been circling comet 67P, is now aligned with Philae so that they can talk to each other—as long as Philae has eked out enough power and warmth from its limited sunlight. “We don’t think we’ll hear anything just yet, but we cannot be very sure,” says Koen Geurts, the technical manager of the Philae team.
Lacking communication with Philae, scientists still don’t know exactly where it is and what its surroundings are like. Engineers have used Rosetta’s cameras to narrow down its location, but the orbiting spacecraft is currently too far away to spot the lander. Rosetta will swoop in closer in July, but as of now, engineers can only estimate that Philae is only getting 1.3 hours of sunlight for each 12.4-hour day on the comet. For the lander to wake up, its solar panels have to be turning those meager hours of sunlight into 5.5 watts of power. And to send and receive signals from Rosetta, it needs 19 watts. Philae also has to be warmer than -49˚F to work. “We do not expect that this is already the case,” Geurts says. “We think Philae is still cold.” In its shadowy hole, Philae’s temperature may have dropped to as low as -150˚F, and even though comet 67P is getting closer to the sun—Philae’s getting twice as much solar energy than it did in November—the spacecraft probably needs more time to thaw.
But as Philae is still out-of-sight, it could turn out to be in a sunnier place, charged up and ready to go. When or if it wakes up, engineers will take a couple weeks to make sure it’s still working. At least at first, it may be too cold for Philae to fully charge its battery, which will limit how much science it can do. “Without the battery, science activity can only last as long as sunlight,” Geurts says. That means Philae won’t be able to drill into the icy comet and find out exactly what it’s made of. But it should still be able to do lower-intensity jobs like take pictures, measure the comet’s magnetic field and seismic activity, and sniff the surrounding gases.
Now that Rosetta and Philae have open lines of communication, mission controllers have commanded the orbiter to start sending signals to Philae starting at 12:00 am EDT. They’ll continue trying to contact Philae until March 20, when Rosetta’s changing orbit puts it out of position. “If we don’t hear anything in this opportunity, then we hope for the next one,” Geurts says. That next window of opportunity will come between April 13 and 20. If nothing then, several shorter windows open in May, and a longer period opens in June.
On August 13, the comet will reach its closest point to the sun—and if the European Space Agency hasn’t heard from it by then, they’ll call it quits. With increasing sunlight, ice will sublimate into gas, creating jets and gassy gusts that can knock Philae out.
Full article: http://www.wired.com … t-enough-power-wake/