A few hours ago, the Electrical Support System Processor Unit aboard the Rosetta spacecraft was switched off. And with it, the communications link between Rosetta and the little Philae lander.
The last time we heard from Philae was just over a year ago. Seven months after that contact, mission controllers knew the likelihood of hearing from the lander was slim. But they kept the communications link active in the off chance they might hear from it again.
“We are not sending commands any more and it would be very surprising if we were to receive a signal again,” said Philae project manager Stephan Ulamec back in December.
Dust-covered solar panels from the comet’s active months near perihelion combined with frigid temperatures in the shade are the most likely causes for Philae’s silence.
The decision to cut the communications link between Rosetta and Philae comes as Rosetta prepares for its own end. As July wraps up, the Rosetta spacecraft will be about 520 million kilometers (323 million miles) from the Sun. At these distances, the spacecraft will lose about 4 watts per day according to the European Space Agency.
With two months of science gathering left, mission controllers are switching off any non-essential components aboard the spacecraft. Since Philae hasn’t ‘talked’ to Rosetta in more than a year, it was on the chopping block.
Why can’t Rosetta hibernate?
It’s a good question. The spacecraft hibernated for 31 months during the most distant part of its trek to Comet 67P. This time is different though. Back then, it was drifting through space right beside a comet. Plus, Comet 67P is traveling away from the Sun. At its maximum distance, it’ll be more than 850 million kilometers away from the Sun.
Scientists aren’t 100% sure that Rosetta will have enough power at these long distances to keep its heaters running and the spacecraft warm enough to survive. Instead, the mission team is opting to follow in Philae’s footsteps. A comet landing.
Rosetta will gather what the ESA calls “once-in-a-lifetime measurements.” These will include high-resolution images from just a few hundred meters above the surface.
Here’s an image of Comet 67P captured from 5 kilometers away.
Imagine the quality we’ll see from Rosetta’s final moments.
Rosetta’s end starts in August
September 30th is the day Rosetta will hit the comet at 50 cm/s (about half of Philae’s landing speed). But the maneuvers to get the spacecraft in place will get underway much sooner.
Rosetta operators will start tweaking the spacecraft’s trajectory starting in August. Once these maneuvers begin, each elliptical orbit will bring it closer and closer to the comet.
“Planning this phase is in fact far more complex than it was for Philae’s landing,” says Sylvain Lodiot, the spacecraft operations manager for Rosetta. “The last six weeks will be particular challenging as we fly eccentric orbits around the comet – in many ways this will be even riskier than the final descent itself.”
The tricky part is the comet itself. It’s not a round object with consistent gravity. As Rosetta’s orbits bring it closer and closer, the folks controlling the spacecraft will need to be ready to make course corrections. The final course correction takes place 12 hours before scheduled impact.
Rosetta’s team recently announced where they intend to crash Rosetta – the Ma’at region.
Let’s cover a couple of more questions.
Will Rosetta be able to communicate after landing (crashing)? Probably not. Rosetta wasn’t designed to land. The solar panels will likely be damaged upon impact, and Rosetta may tumble like Philae did. Even if it does survive unscathed, Rosetta’s high-gain antenna will have to be pointed towards Earth. If it’s off by just half a degree, ground stations on Earth won’t receive any signal.
But we’ll have communications during descent, right? Rosetta’s team thinks so. The high-gain antenna will be pointing towards Earth, but there will be some issues here as well. From Earth, Rosetta and the comet will appear to be very close to the Sun. That will make gathering data and sending signals challenging.
If everything works out, Rosetta will give us the best images ever captured of a comet.