European Space Agency Picks Site For First Comet Landing In November

An anonymous reader writes Europe's Rosetta mission, which aims to land on a comet later this year, has identified what it thinks is the safest place to touch down. From the article: "Scientists and engineers have spent weeks studying the 4km-wide "ice mountain" known as 67P, looking for a location they can place a small robot. They have chosen what they hope is a relatively smooth region on the smaller of the comet's two lobes. But the team is under no illusions as to how difficult the task will be. Comet 67P/Churyumov-Gerasimenko, currently sweeping through space some 440 million km from Earth, is highly irregular in shape. Its surface terrain is marked by deep depressions and towering cliffs. Even the apparently flat surfaces contain potentially hazardous boulders and fractures. Avoiding all of these dangers will require a good slice of luck as well as careful planning.

Comments

Does it look like a potato?

[Quantum Apostrophe]

Does it have inner chambers? One of which goes on forever?

Re:Does it look like a potato?

[JaneTheIgnorantSlut]

No, but it does have a maze of many twisty passages, all alike.

A good slice of luck.

[Thanshin]

Avoiding all of these dangers will require a good slice of luck as well as careful planning.

"A good slice of luck"? Seriously?

Whoever managed to get approved a project plan with that caveat, is my new god.

Re:A good slice of luck.

[gstoddart]

I think it's a recognition that what they're doing is incredibly hard, and you can plan all you want, but there's still going to be stuff which isn't within your control.

We're talking about setting something down on a spinning body which is really far away, and which there is likely a very long delay in any of your controls.

As much as we like to think space stuff is pretty commonplace, it's not exactly a small undertaking to try to do this.

I'm betting the people who oversee this know damned well the risks, and are trying to manage the public perception of it ... because if it goes wrong you're going to get tons of people saying "Yarg! I could have done better".

Re:A good slice of luck.

[Lab Rat Jason]

My understanding is that gravity irregularities (caused by the lobular shape, as opposed to a spherical shape) are going to be one of the biggest challenges. How do you calculate the correct amount of thrust when gravity decreases as you get closer to your landing spot? All these things need to be accounted for, and there are plenty of unknowns still.

Shame we can't watch it real-time... that would be a popcorn moment no doubt.

Re:A good slice of luck.

[gstoddart]

However, "a good slice of luck" doesn't belong at news about arguably the recent highest engineering achievements of humanity.

Why not? It's an honest assessment of the task at hand.

According to TFA:

Esa says it will be a one-shot opportunity. Events will be taking place so far away that real-time radio control will be impossible.

Instead, the process will have to be fully automated with the final commands uploaded to Rosetta and Philae several days in advance.

So, basically you plan as much as possible, do everything you can ... and then when it happens, you're in the dark, and it either will or won't have worked. But you'll have had to send everything a few days in advance, and you'll be sitting and hoping when it really happens.

I think it's at least honest and open about the real challenges. Because when you have to rely on the automated stuff working 100% perfectly, and you have no chance to correct anything, you still are coming down to luck.

Would you rather they acted like there was no luck involved in this?

This isn't parallel parking your car. This, as you say, is some of the most complex engineering around. And the people doing it are under no illusions that they have it completely under control.

I have no problem with them pointing out how just how hard this is. If it works, they're rock stars. If it fails, then they've at least been up-front about the limitations of what they're able to do.

Re:A good slice of luck.

[wooferhound]

The lander does not have any capability to steer itself once released. The orbiter will reduce it's orbit down to 10km and the lander will be pushed away from the orbiter at walking speed, if there is a boulder underneath, there is no way to maneuver away to another landing location. This is why there is a lot of luck involved.Gravity is very low, if there were an astronaut on the surface they could jump off and achieve escape velocity. The lander does not have any way to slow down when it nears the surface and when it makes contact it will harpoon the surface and use screws to secure it down securely.

Re:Sounds challenging.

[jandersen]

It would be very strange indeed to find an object in space that doesn't rotate at all - any external influence on an irregularly shaped object is likely to result in a change in rotation. In fact, it holds true even for a spherical object in a gravitational field, since that field will vary over the diameter of the object.

Do they know the gravity field vectors?

[wisebabo]

I would think that on such a wildly irregular body (the topology has been likened to a rubber duck), not only does the strength of the comet's gravity vary from place to place but the DIRECTION does as well. Something that appears to be "flat" or horizontal may, in fact, be a steeply sloping surface because the gravity vector is not perpendicular to the surface. Of course if it the surface were a liquid or very fluid particles then the surface would always be perpendicular to the local gravity vector but it appears as if it is made of a very heterogenous bunch of materials some of which are rigid (like rocks).

Then again, the surface gravity is likely to be so small (1/100th of a gee? 1/1000th of a gee?) that maybe it doesn't matter. From what I understand the probe has to harpoon itself to the surface; though I don't know whether that is because the gravity is so low that it might just bounce back off into space or because of the outgassing from the comet as it approaches the sun will threaten to "blow it away".

Too bad the comet's orbit doesn't have its closest point closer to the sun, I'd expect some real "fireworks". As it is, I'm not sure how much outgassing they expect.

Spider legs

[dkman]

So apparently what we need to develop is a better landing leg configuration that doesn't care about a flat surface. Something like spider legs that could have a rough surface underneath, but with each leg bent differently so that the cargo body is level. Granted, on Earth's surface "level" means something, on a 4 kilometer comet that may be more difficult to determine.

I feel that legs could also absorb some impact from the landing as well. Think along the lines of bending your knees as you land from a jump.

I understand that there a plenty of complexities in getting your robotic spider overlord into space, but you've gotta admit it would look pretty bad-ass walking around on an ice comet. Making the joints tolerant of the temperatures might be another thing to worry about, but if we've got the wheel joints figured out it's probably not a big leap from there.

Re:Sounds challenging.

[cusco]

Actually the comet does not have enough gravity of its own to allow the spacecraft to orbit it, so Rosetta is in a solar orbit just inside of 67P. Since in that orbit it would quickly outpace the comet ESA has devised a generally triangular flight path that keeps it relatively close while enabling the best use of solar illumination.