Yesterday's heroic comet landing was crazier than mission controllers had hoped for. After two wild bounces and no harpoon strikes to anchor it, Philae has settled in the shadow of a cliff. One of its three feet is off the ground. Worse, there there are now concerns about its battery life.
"Philae is on the surface and doing a marvellous job, working very well and we can say we have a very happy lander," noted ESA team member Paolo Ferri earlier today.
It's an overly rosy assessment that belies the reality of the situation.
Indeed, the Philae landing featured some serious technical glitches that are surely frustrating mission planners.
The entire mission was nearly scrapped yesterday when controllers detected problems with the cold gas thruster. But they went ahead with the landing anyway, since a delay would not improve the situation. Then, as the probe reached the surface, the harpoons failed to fire. What's more, its feet screws have not latched on to the surface. There's now concern about the longer-term stability of the probe as it's not properly anchored.
The controllers are now contemplating whether to have Philae make another attempt at firing the harpoons, but that could throw Philae back off into space. The gravity is so low on the comet that even a flea could exert enough jumping force to attain escape velocity.
Controllers are also concerned about drilling into the comet, as this too could affect the stability of the lander.
Indeed, Philae had quite the landing yesterday. Or rather, landings. It made first contact with the surface at 15:33 GMT and then bounced nearly one full kilometer (0.62 miles) back up. It's not immediately clear what this initial bounce looked like; it could have bounced straight up, or at some extreme angle relative to the surface. But nearly two hours later, at 17:26, it bounced yet again. It finally landed for good at 17:33.
"After our first touchdown signal we could tell that something was not normal because Philae was still moving. The lander kept rotating," noted Stefano Mottola from the Lander Control Centre. That was obviously a troublesome sign. Controllers worried that Philae would not make contact with the comet again, but after nearly two hours, "we saw that the rotation stopped. The rotation could only stop by touching the comet again."
This second hop was a small one, lasting for about seven minutes.
This is the location of the first touchdown point of the Philae lander. The image was taken by the OSIRIS camera onboard Rosetta at a distance of 50 km (31 miles).
That means Philae is nowhere near its intended landing site. Given the length of time it was adrift, and given that the comet rotates once every 12 hours, the probe may have travelled across one-sixth of the comet's surface.
During an ESA press conference earlier today, mission controllers showed an image indicating Philae's possible location on the far side of a large crater that was considered — but ultimately rejected — as a suitable landing site.
"I was joking that we jumped from one 'preselected landing site to another,'" said Stefan Ulamec, head of the lander team.
Frustratingly, Philae appears to have settled in the shadow of a cliff — about one kilometer from its target site. It may be difficult for the probe to get enough sunlight to charge its batteries.
Despite all this, the lander managed to snap a picture (as shown at very top). And indeed, its resting place does not look very hospitable. The black-and-white image shows one of the lander's three feet, some rather jagged looking rocks, and a very dark patch.
Philae, where are you? This five-image montage is being used to try to identify the final touchdown point of the lander.
"We could be somewhere in the rim of this crater, which could explain this bizarre… orientation that you have seen," noted Ulamec.
Determining Philae's exact location and orientation will require some time. Thankfully, the lander is sending "great data" from several different onboard instruments.
It may be possible to reconfigure the lander's gear and "hop" to a new location, but there may not be enough time to do the analysis required for such a risky operation. Philae is not getting as much power from the sun as planned. The batteries will last through tomorrow, but perhaps not beyond the 60-hour mark. At that point, Philae could be put into a hibernation mode and awoken in a few months, if more solar energy hits its position. That's a rather big if.
"If even in months the solar situation will change completely, we can still wake it up," added Ulamec.
We will continue to update this story as images and data come in throughout the day.
[ ESA ]