European Space Agency Picks Site For First Comet Landing In November 35
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.
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The probe is in orbit around the comet, and a quite peculiar orbit too. So regardless of what the comet does, from the reference point of the probe, it is "rotating".
Re:Sounds challenging. (Score:4, Informative)
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.
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The triangular path is only the approach path. The goal is to reach a stable orbit around the comet,.
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The probe is in orbit around the comet, and a quite peculiar orbit too. So regardless of what the comet does, from the reference point of the probe, it is "rotating".
I don't think so. The comet may not be rotating on its own. Which would mean that all patches of its surface rest in an inertial frame (at least if you ignore the rotation around the sun -- which shouldn't have much influence during the short timespan of a landing). If that were the case, it would make the landing easier because the lander's velocity relative to the surface would stay constant during unpowered flight phases.
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I believe 67P is indeed tumbling, but I can't find a reliable reference to that information.
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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.
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But classical gravity varies with the inverse square of the separation, and half of a sphere will be more separated than the other half - hence the tidal force experienced by an orbiting satelite. This effect will only vanish if the two bodies are moving on a straight line through the two centres of gravity of each.
Does it look like a potato? (Score:2)
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Sorry, but it's a bit early for that. Search for "Patricia Vasquez" and you find two of any prominence, an acress and someone who mediates natural resource problems. Add "mathematics" to the search and the top hit is utterly irrelevant - some dude named Greg Bear.
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A good slice of luck. (Score:3, Insightful)
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. (Score:4, Insightful)
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".
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I don't dispute the recognition of a random chance of nasty boulder on the landing spot. I do dispute the vague quantification of such risk.
I wouldn't have a problem with "The chosen spot has an estimated 2% chance of unavoidable crashing conditions.". However, "a good slice of luck" doesn't belong at news about arguably the recent highest engineering achievements of humanity.
Re:A good slice of luck. (Score:5, Insightful)
Why not? It's an honest assessment of the task at hand.
According to TFA:
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.
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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.
What amazes me is that the lander has no RCS - it's launched at the comet, and if it bounces off or something there is no second go. I kinda expected the lander to have some RCS so it could automatically correct for unexpected troubles.
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Mass. Remember, this thing has taken a decade to even **GET** to the comet, if they had added more mass they very likely could not have reached the comet at all with the launchers available to them.
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You can't expect to have every detail in the Slashdot summary. The article does give a precise quantification of the risk: it says "Pre-mission analysis suggested the chances of a successful landing on roughly spherical body to be 70-75%."
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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.
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sounds reasonable to me. Hell, in the first manned moon landing the landing zone was determined to be too rocky (as in littered with large boulders) and so the crew took manual control; counting off altitude as they descended. Compared to this thing, the moon may as well be smooth as a bowling ball.
It almost challenges your notion of what a "slope" is since it is really defined by the perpendicularity of the surface with respect to the force of gravity. At least the Apollo guys could just look down at the s
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Do they know the gravity field vectors? (Score:3)
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.
Do they know the gravity field vectors? (Score:1)
67P is estimated to have an acceleration of gravity of about 1 x 10 -3 m/s2 (0.001). Or about 1/10000 that of Earth. For comparison I think your average ion thruster has a acceleration of about 0.000092 m/s2, and has been likened to the pressure put on your hand by earth gravity of a single piece of letter paper. So its not inconsequential, but even so if you dropped something from about a mile, by the time it reached the surface it would only be going about 3.5 MPH. Assuming I haven't become to rusty w
That's all fine and good, (Score:2)
Spider legs (Score:2)
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
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Problem with that is there isn't enough gravity for your spider to be able to walk, about 1/10,000 g. Every leg thrust, no matter how weak, would bounce the thing up off the surface. Rather than looking all bad-ass walking around, your robotic spider would look rather silly bunny-hopping about.