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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.
Does it have inner chambers? One of which goes on forever?
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.
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 believe 67P is indeed tumbling, but I can't find a reliable reference to that information.
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.
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.
so long as they don't try to land a damn comet anywhere near me!
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.
I refuse to sign
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 with my math/unit conversion.
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.
"Think about how stupid the average person is. Now, realise that half of them are dumber than that." - George Carlin
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.
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.
The triangular path is only the approach path. The goal is to reach a stable orbit around the comet,.