Philae probe bounces on a comet…

Welcome_to_a_cometRosetta and Philae are now in contact again, and we have more detail on yesterday’s landing, including the first part of a panoramic image of the probe’s surrounding, including what looks like a craggy cliff. Yesterday mission team members told us that they think that Philae bounced, and now they believe it bounced three times before settling in to its current location.

To understand how this happened, it might be useful to change the way we think about the “landing”. 67P’s gravity is tiny compared to Earth or the Moon…the lander weighs about as much as a first-class letter on the comet’s surface. Instead of thinking about a descent and a landing, it might be better to think of it as an approach and a grab. Philae traveled to the surface of the comet, bumped into it, and tried to attach itself with its harpoons. Its approach was very slow, but it still bounced, which means the surface was different than everyone expected. Here is an image of the first landing impact site:


The “bounce” from this site sent Philae a few hundred meters to a whole kilometer from the surface (“above” is not a good word to use here, again due to the very low gravity). Mission scientists are trying to figure out where the lander is now. Here is an earlier estimate of where it might be. The red square is the initial impact site, the blue triangle where they suspect Philae is now.

landing siteThe lander’s situation is precarious. The harpoons designed to tie the lander to the comet did not fire, and now the mission controllers are leery of firing them, in case they push the probe right off 67P and send it flying off into space. In fact, they now have to consider very carefully any movement by any part of the lander, including the research drill. There is also an opportunity here to use the lander’s moving parts not as originally intending, but as “arms” to reorient the probe itself.

Power is an issue. Mission Control thinks that the lander’s solar panels are partially in shadow, making power a concern. They will have to figure out how much they power they can generate and calibrate the lander’s activities accordingly. It can’t do too much too fast or it might drain the batteries too much.

As we’ve seen with other robotic missions like the twin Mars rovers Spirit and Opportunity, there are lots of ways to problem solve, even via remote control from more than 300 million miles away, and there are familiar analogues to Philae’s current situation in other mission histories. My bet is that Philae will keep surprising us!


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