Rosetta: “We’ll need some luck not to land on a boulder or a steep slope.”

Rosetta Mission selfie at 16km from Comet

[Image credit: ESA/Rosetta/Philae/CIVA] The ESA Rosetta probe has been on a long journey – spotted en route briefly on Slugger in 2008, and more leisurely in 2010 as it took time out from its mission to the Comet 67P/Churyumov-Gerasimenko to take a look at the asteroid Lutetia.  Ten years after launch, it’s now orbiting its designated target, and the lander, Philae, is descending.  However, there has been a hiccup…

During checks on the lander’s health, it was discovered that the active descent system, which provides a thrust to avoid rebound at the moment of touchdown, cannot be activated.

At touchdown, landing gear will absorb the forces of the landing while ice screws in each of the probe’s feet and a harpoon system will lock Philae to the surface. At the same time, the thruster on top of the lander is supposed to push it down to counteract the impulse of the harpoon imparted in the opposite direction.

“The cold gas thruster on top of the lander does not appear to be working so we will have to rely fully on the harpoons at touchdown,” says Stephan Ulamec, Philae Lander Manager at the DLR German Aerospace Center.

“We’ll need some luck not to land on a boulder or a steep slope.”

“There were various problems with the preparation activities overnight but we have decided to ‘go’. Rosetta is lined up for separation,” says Paolo Ferri, ESA’s head of mission operations.

The BBC science report includes a look at the landing site.

Rosetta Comet landing site

Philae is scheduled to land on the comet some time after 3.30pm, with confirmation signal expected around 4pm [GMT]. You can follow events as they unfold on the Rosetta blog, or  via the live-streaming video from Rosetta mission control

As the BBC science report notes,

Not only is landing on a comet an untried technique, but Wednesday’s effort is also having to rely on some relatively old technologies.

Rosetta was despatched from Earth to catch 67P in 2004. That means it and Philae were designed and built in the 1990s.

And given the conservatism of space engineering, a number of its onboard systems will therefore undoubtedly be 1980s vintage.

But even if the landing attempt fails, the pictures and measurements of 67P acquired by the Rosetta mothership in recent weeks will be enough to re-write the textbooks.

“The real scientific value of this mission is spread all over Rosetta and its instruments, and the lander is just a part of that,” explained Esa flight director Andrea Accomazzo.

“The lander is obviously spectacular; it’s the thing the public recognise. But already, even before the landing, the scientific return of Rosetta is orders or magnitude above what we knew about comets previously.”

Indeed.

Update Philae has just landed on a comet!

Adds But there may be a problem…

A European robot probe has made the first, historic landing on a comet, but its status remains uncertain after harpoons failed to anchor it to the surface.

Officials said the craft may have lifted off the comet after touchdown before returning to the surface.

Lander project manager Stephan Ulamec said: “Maybe we didn’t just land once, we landed twice.”

Further analysis is needed to fully understand the situation.

However, Dr Ulamec told the BBC that at last radio contact with the probe that he believed it to be in a stable configuration.

“This is the indication right now,” he explained. “We really have to wait until tomorrow morning and then we will know a lot more.”