Scientists controlling the Philae lander on Comet 67P/Churyumov–Gerasimenko are preparing to make a last ditch attempt to “hop” the robotic probe into a sunnier spot on the comet’s surface.  If they fail, the lander will go into hibernation. Without sufficient sunlight on its solar panels, its mission will be over.  The lander’s legs have a built-in spring action that can be commanded to fire. These commands will be uploaded tonight during an expected communications window that opens at around 21:00 GMT. There is no guarantee of success.  Time is running out for the European Space Agency’s lander. Since its bumpy triple touchdown on Wednesday, the spacecraft has been resting on its side, lodged in the shadows of a cliff or large boulder. On Thursday, the lander sent back historic first images taken from the surface of a comet. These showed that after its bumpy triple touchdown one of its legs is sticking up into space rather than in contact with the surface. So there may not be enough spring in Philae’s step to achieve the hop.  The lander is surrounded by rocks with only a sliver of light reaching one of its smaller solar panels. Philae has been receiving just 1.5 hours of sunlight instead of the expected 6-7 hours. “We are unlucky, in a corner, surrounded by rocks,” says Valentina Lommatsch from DLR’s lander team.  So far, the lander has not moved at all, despite science instruments deploying a 1.2 metre arm and a drill that could have induced a “equal and opposite reaction” movement in the lander.  A bolder strategy under discussion is to spin up an internal flywheel that could make Philae cartwheel out of its predicament. But the flywheel consumes a lot of power and there may not be enough left in the batteries for this to work.  Philae’s primary mission was always designed to last around 60 hours. Engineers then covered the spacecraft in solar panels in the hope that sunlight could recharge a set of secondary batteries and extend the mission for months.  Despite the awkward landing, Stephan Ulamec, Philae lander manager, DLR, estimates that 80% of the science Esa was hoping for has been achieved. If the current drilling operation works and Philae delivers samples to one of its onboard instruments, that will rise to 90%.  The COSAC (Cometary Sampling and Composition experiment) instrument has been chosen for the first samples rather than the UK-built PTOLEMY instrument. COSAC detects and identifies complex organic molecules from their elemental and molecular composition.  Ulamec says the choice was made because COSAC uses less power than PTOLEMY, and provides data that can be more easily compared to that taken from the Rosetta orbiter.  PTOLEMY has still generated data by working in ‘sniffing’ mode. Essentially, the instrument has detected and analysed molecules of gas that have naturally drifted off the surface of the comet.  “We juggled everything so that every instrument got to do a measurement, so we are very happy with the mission so far,” says Lommatsch.  If the attempts at moving the lander do not work, then tonight’s communications window will almost certainly be the last one in which the scientists can talk to the lander. But all might not be lost forever.  The comet is currently out beyond the orbit of Mars, heading for its closest approach to the sun in August 2015. This will bring it as close to the sun as Earth’s orbit. There the sunlight will be brighter and may just allow Philae to re-boot and power up.  “Cross your fingers, or press your thumbs if you are a German, that we hear something from the lander again,” said Lommatsch.
Order will be sent to Philae’s legs this evening in a bid to bounce the comet lander into a sunnier position to recharge its batteries