|Philae lander harpooned into comet|
Excerpt from online.wsj.com
Scientists at the European Space Agency fear that the Philae probe now sitting on a comet’s surface may be on the verge of running out of battery power, a scenario that could bring key scientific experiments to a premature end.
The researchers will only know whether the primary batteries have drained or not late Friday, when they try to re-establish a radio link to the probe via Rosetta, a spacecraft in orbit around the comet. The probe and Rosetta can typically communicate twice a day because at other times the orbiter is below the horizon and can’t establish a direct signal.
Scientists are hoping to get contact around 10 p.m. German time, said Stephan Ulamec, who oversees operation for the lander. But if Philae fails to send a signal, he added, it would mean the battery had run out of juice.
The plan was for Philae to do scientific experiments for an initial 2 ½ days on primary battery power and then switch to solar panels that would keep it ticking for another three months. But because of an awkward landing near the face of cliff, the probe’s solar panels are being exposed to far less sunlight than was expected.
Despite the hitch, Philae has already done a significant amount of science on its new home. Its 10 instruments have so far garnered between 80%-90% of the data they were designed to collect, according to Dr. Ulamec.
It has beamed back detailed photographs of the comet’s rough terrain, analyzed the gases, and taken the comet’s temperature. It is now using radio waves to probe the comet’s nucleus and searching for organic molecules on the hostile surface.
Anticipating a possible loss of battery power, ESA scientists activated a drill during their last contact with the lander. The machine is designed to dig up the comet’s subsurface material and rotate it through an onboard oven to investigate its components.
There may still be a way to extend Philae’s working life. During every 12-hour rotation of the comet, one of the lander’s solar panels is now exposed to an hour and 20 minutes of sunlight, while two other panels get the sun for less than 30 minutes each.
Provided the signal to Philae can be re-established, scientists said they could rotate the lander slightly so that one of its larger solar panels can catch more sunlight. Another option is to eject the probe from its current location in the hope it lands in a spot where there is more sun.