When the European Space Agency (ESA) deployed the Philae lander from its Rosetta spacecraft on November 12 of last year, it was a landmark achievement: Upon making contact with Comet 67P/Churyumov-Gerasimenko, it marked the first time mankind had landed a probe on a moving comet. After several hours worth of data transmission, they have a new challenge: Philae doesn’t want to wake up.
“We are sure that the communication unit on the orbiter worked, but whether Philae has received the new commands, we do not yet know,” says Koen Geurts, a member of the control room team at DLR, in reference to a communication attempt that began on March 12 and ended on Friday.
Upon landing on November 12, Philae operated for 54 continuous hours, with all of its instruments working properly and transmitting data back to Earth via Rosetta. Once its battery was exhausted, however, Philae went into hibernation mode in what the ESA says is a particularly shadowy location. That’s important, because solar energy is essential for Philae to be able to generate its own power.
The issues Philae faces are twofold: One, Philae must reach an internal temperature above -45 degrees Celsius before it’s even capable of turning on. The ESA knew that would be virtually impossible in January and February, and didn’t bother trying to communicate with it. Beyond temperature, it also needs at least five watts of power just to turn on. In order to transmit data, it needs to build up at least 19 watts. Though the solar radiation reaching the comet is nearly double what it was in November, it’s apparently not yet enough.
In fairness, the astronomers knew that reconnecting with Philae was wishful thinking.
“It was a very early attempt; we will repeat this process until we receive a response from Philae,” says DLR Project Manager Stephan Ulamec. “We have to be patient.”
The next communication attempt is planned for the first half of April. Even if solar radiation is such that Philae might have enough power and warmth to work, it’s still a delicate operation. Because Rosetta (which is responsible for sending information to Earth) is orbiting the comet, its orbit needs to align with Philae receives enough radiation while Rosetta is in transmission range. It would need optimal conditions for at least 45 minutes, owing to the fact that Philae only operates its receiver every 30 minutes after reactivation.
As the comet rockets closer to the sun in the summer months, the ESA fully expects Philae to return to form and carry on with its duties. In the mean time, they have faith that the lander will weather its hibernation successfully.
“Philae is configured in an optimal way for on-comet survival,” said Geurts.