Starting tomorrow, scientists from the European Space Agency (ESA) will attempt to make contact with the stricken Philae lander for the first time in nearly four months.
Philae is in the shade — not good for solar power
The spacecraft successfully touched down on comet 67P/Churyumov-Gerasimenko in November last year, but an unexpectedly bouncy landing left it stranded in an area far colder and with far less sunlight than scientists had originally planned. The craft was able to carry out a number of experiments over the next three days, but eventually entered a low power state before it ran out of power. Now, as the comet draws closer to the Sun and receives more heat and light, scientists are hopeful it will awaken again in the coming weeks, to finish off the work it started.
"Philae currently receives about twice as much solar energy as it did in November last year," says the lander's project manager Stephan Ulamec. "It will probably still be too cold for the lander to wake up, but it is worth trying. The prospects will improve with each passing day."
A gif of Philae's descent to comet 67P.
For Philae to wake up completely, the interior of the craft must be at least -45ºC and its solar panels must be receiving a minimum of 5.5 watts of power. Once its core systems realize that these criteria have been met, the lander will attempt to charge its battery, switching on its receiver every 30 minutes to listen for instructions from the orbiting Rosetta. Scientists say it's possible that Philae has already woken up, but that the lander doesn't yet have enough power to communicate with Rosetta.
"At this time, we do not yet know that the lander is awake," says Koen Geurts of the Rosetta control center. "To send us an answer, Philae must also turn its transmitter – and that requires additional power."
Philae gets 1.3 hours of sunlight per cometary "day"
Between the 11th and 20th of March, Rosetta will make a number of flybys during Philae's daytime — that is, when the side of the comet its on is exposed to sunlight. A day on 67P currently lasts 12.4 hours and scientists believe that Philae is only exposed to the Sun for 1.3 hours every day — not even half of what was planned for. If initial communication is made in the next few weeks, scientists can begin checking on Philae's condition. "We will then evaluate the data," says Geurts. "What is the state of the rechargeable battery? Is everything on the lander still functioning? What is the temperature? How much energy is it receiving?"
Even if this initial attempt at communication doesn't work, ESA scientists are hopeful that they will have more chances in the future as the comet gets closer to the Sun. "If we cannot establish contact with Philae before 20 March, we will make another attempt at the next opportunity," says Ulamec. "Once we can communicate with Philae again, the scientific work can begin."