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European Space Agency Picks Site For First Comet Landing In November

Posted by samzenpus on from the x-marks-the-spot dept.

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.

35 comments

  1. Sounds challenging. by Anonymous Coward · · Score: 0

    Is it rotating? Perhaps even about multiple axes? That could be like a blowfly trying to land on one of Aaron Rodger's bombs.

    1. Re:Sounds challenging. by geogob · · Score: 1

      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".

    2. Re:Sounds challenging. by Thanshin · · Score: 1

      I believe 67P is indeed tumbling, but I can't find a reliable reference to that information.

    3. Re:Sounds challenging. by jandersen · · Score: 2

      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.

    4. Re:Sounds challenging. by cusco · · Score: 3, 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.

      --
      "Think about how stupid the average person is. Now, realise that half of them are dumber than that." - George Carlin
    5. Re:Sounds challenging. by Anonymous Coward · · Score: 0

      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.

      Classical gravity can not induce a torque on a perfectly spherically symmetric body. For every point in space with mass applying gravitational force to the body, there will be a perfect symmetry on both sides of the line between the point and the center of the body. If no point in space can apply a torque, no integral over whatever mass distribution you have will either. You can only get a torque if there is some asymmetry.

    6. Re:Sounds challenging. by multi+io · · Score: 1

      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.

    7. Re:Sounds challenging. by jandersen · · Score: 1

      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.

    8. Re:Sounds challenging. by geogob · · Score: 1

      The triangular path is only the approach path. The goal is to reach a stable orbit around the comet,.

  2. Does it look like a potato? by Quantum+Apostrophe · · Score: 2

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

    1. Re:Does it look like a potato? by dpilot · · Score: 1

      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.

      --
      The living have better things to do than to continue hating the dead.
    2. Re:Does it look like a potato? by wooferhound · · Score: 1

      My God . . . it's full of stars

      --
      We are Dead Stars looking back Up at the Sky
    3. Re:Does it look like a potato? by JaneTheIgnorantSlut · · Score: 2

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

  3. A good slice of luck. by Thanshin · · Score: 2, 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.

    1. Re:A good slice of luck. by Anonymous Coward · · Score: 0

      Space is hard; space stuff nobody has done before is even harder. Space stuff on an unstable thing of uncertain composition, even harder still.

      A good slice of luck is exactly right.

    2. Re:A good slice of luck. by gstoddart · · Score: 3, 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".

      --
      Lost at C:>. Found at C.
    3. Re:A good slice of luck. by Thanshin · · Score: 0

      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.

    4. Re:A good slice of luck. by Lab+Rat+Jason · · Score: 2

      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.

      --
      Which has more power: the hammer, or the anvil?
    5. Re:A good slice of luck. by gstoddart · · Score: 5, Insightful

      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.

      --
      Lost at C:>. Found at C.
    6. Re:A good slice of luck. by Anonymous Coward · · Score: 1

      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%."

    7. Re:A good slice of luck. by Anonymous Coward · · Score: 0

      The "luck" part is Philae's landing ellipse. If they're off by even a few tens of meters they might hit something or sail off into space.

    8. Re:A good slice of luck. by Anonymous Coward · · Score: 0

      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.

      We're talking about landing on a rock hurtling through space.

      From an approval standpoint, it's a miracle someone approved this idea beyond the pool of spilled bong water it was birthed from.

    9. Re:A good slice of luck. by Anonymous Coward · · Score: 0

      "Probe crash-lands on comet, first for mankind!"

      "Probe touches comet, comet sues probe"

      "Comet declares Crimea to be part of it's dominion"

      "Comet complains it's got a right for privacy and ESA should stop taking pictures of it"

    10. Re:A good slice of luck. by TheCarp · · Score: 1

      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 surface and approximate that gravity is pulling them down into it.

      --
      "I opened my eyes, and everything went dark again"
    11. Re:A good slice of luck. by wooferhound · · Score: 2

      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.

      --
      We are Dead Stars looking back Up at the Sky
    12. Re:A good slice of luck. by FireFury03 · · Score: 1

      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.

      --
      http://blog.nexusuk.org
    13. Re:A good slice of luck. by cusco · · Score: 1

      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.

      --
      "Think about how stupid the average person is. Now, realise that half of them are dumber than that." - George Carlin
    14. Re:A good slice of luck. by Yoda222 · · Score: 1

      The goal is get more information about comets. The only way to reduce the luck in the mission is to get more information about comets. You could probably make two mission, the first one studying a comet, the second one having a landing device. But you will not be sure that the second comet that you visit is similar to the first one. And it will cost a lot more. So adding a secondary landing probe to Rosetta, even if it may fail, is a cheaper solution, yet relying on some luck.

  4. Do they know the gravity field vectors? by wisebabo · · Score: 2

    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.

    1. Re:Do they know the gravity field vectors? by Anonymous Coward · · Score: 0

      Not very rusty at all sir. 'Walking pace', they say, which is .7 furnicals purlent per fortnight.
      Which means try to hang on if you get there or that piece of A4 will bounce you back.

  5. That's all fine and good, by WillgasM · · Score: 1

    so long as they don't try to land a damn comet anywhere near me!

  6. Spider legs by dkman · · Score: 2

    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
    1. Re:Spider legs by cusco · · Score: 1

      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.

      --
      "Think about how stupid the average person is. Now, realise that half of them are dumber than that." - George Carlin
  7. Do they know the gravity field vectors? by Anonymous Coward · · 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 with my math/unit conversion.

  8. Nice title by blackt0wer · · Score: 0

    Did anyone else read this title and wonder where in the EU they were going to land a comet?