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Space Science

Rosetta, the Comet Hunter 132

Posted by Cliff
from the harpooning-comets dept.
Roland Piquepaille writes: "After being delayed for about a year because of a failure of the Ariane-5 rocket, the Rosetta spacecraft is scheduled to be launched on February 26. Rosetta is a special spacecraft, including an orbiter and a lander. And it will take up to 2014 before landing on Comet 67P/Churyumov-Gerasimenko -- with the help of a harpoon. Then, as says the European Space Agency (ESA), Rosetta will help to solve planetary mysteries. This news release looks at the goals of Rosetta's mission and explains why it will take more than ten years to reach the comet. But here the 'funny' part of the story: the landing. 'In November 2014, the lander will be ejected from the spacecraft from a height which could be as low as one kilometre. Touchdown will be at walking speed, about one metre per second. Immediately after touchdown, the lander will fire a harpoon into the ground to avoid bouncing off the surface back into space, since the comet's extremely weak gravity alone would not hold onto the lander.' This overview contains more details and includes illustrations of the Rosetta's spacecraft and its landing on the comet."
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Rosetta, the Comet Hunter

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  • by corebreech (469871) on Saturday January 31, 2004 @06:09PM (#8146605) Journal
    Harpoon... check

    Name I can't pronounce... check

    10 years before getting some... check

    I just have the class not to make a big deal out of it.
  • Phase 2 (Score:4, Funny)

    by AtariAmarok (451306) on Saturday January 31, 2004 @06:10PM (#8146615)
    Phase 2 will be sending Bruce Willis and the rest of his rigger pals in their awful corduroy space-suits to "kick comet ass" of all the ones found by Rosetta.
  • Gravity? (Score:5, Interesting)

    by Moderator (189749) * on Saturday January 31, 2004 @06:10PM (#8146618)
    The timeline states that in 2014, Rosetta will orbit the comet for six months before it lands, mapping the comet to find a suitable landing spot. Then it goes on to say:
    Immediately after touchdown, the lander will fire a harpoon into the ground to avoid bouncing off the surface back into space, since the comet's extremely weak gravity alone would not hold onto the lander..

    My question is, if the comet's gravity is so weak, how is the Rosetta supposed to orbit this thing for six months?
    • Very slowly? Staying in orbit is just like falling, but you "move out of the way of" the body (comet in this case) you want to orbit so you move next. Repeat this thought-experiment for the new position and so on.
      • Very slowly? Staying in orbit is just like falling, but you "move out of the way of" the body (comet in this case) you want to orbit so you move next. Repeat this thought-experiment for the new position and so on.

        It should of course read .. so you move next to it. My humble appoligies.
    • Re:Gravity? (Score:5, Informative)

      by C17GMaster (727940) on Saturday January 31, 2004 @06:28PM (#8146717)
      From Rosetta's webpage [esa.int]: The relative speeds of the spacecraft and comet will gradually be reduced, slowing to 2 metres per second after about 90 days. If it moves slowly enough, the comet's weak gravity can hold it in.
      • Re:Gravity? (Score:3, Informative)

        by mindriot (96208)

        This is going to be a very difficult mission. I would love to have a job constructing the lander... I am simply amazed by the fact that we're able to hurl a piece of fragile technology at tiny objects in space that are far, far away (yes, considering how big space is, I would call Mars 'small' too) -- and they will actually get there in one piece and work.

        I really hope they'll make it with this one. The German Max-Planck Institute for Aeronomy [linmpi.mpg.de] (soon to be called Institute for Solar System Research) is r

        • Trying to get Rosetta to land on a comet = trying to get an auto pilot bullet to land on a dime without hurting itself.
  • by bc90021 (43730) * <<ten.12009cb> <ta> <12009cb>> on Saturday January 31, 2004 @06:11PM (#8146626) Homepage
    ...given that we probably know little about the surface of the comet.

    Given that it could be porous (or even lots of shatterable ice), I hope that the harpoon has the force to bury itself deeply enough to actually anchor itself in something solid.
  • by mobiux (118006) on Saturday January 31, 2004 @06:14PM (#8146645)
    I know that landing on Mars is a very tough thing, lots of variables to consider.

    But this seems like it would be exponentially harder.
    Ya know, landing on something that doesn't have gravity and they don't know what it's made of.
    • by Darth23 (720385) on Saturday January 31, 2004 @06:16PM (#8146655) Journal
      That's why they should use Duct Tape instead of a harpoon.
    • It's certainly a significantly different kind of problem. You don't have to worry about parachutes and atmospheric entry but the orbital mechanics are extremely tricky due to the weak gravity field.

      Fortunately, they do have some experience to draw upon. NASA's NEAR mission [jhuapl.edu] managed to land on a 21x8x8 mile asteroid named Eros and operated afterwards, despite the fact it was not actually designed to land. Performing that end of mission "stunt" contributed greatly to the overall knowledge of operating ar

    • Of course, there are 3 things Mars have that the comet doesn't.

      1. A gravity, stuff went down... parachute failed... SMACK!
      2. An atmosphere, stuff went down... warm... getting warmer... hot... AH! IT BURNS!
      3. A hot-tempered weather system... Houston, we have a storm in coming... Bz...

  • by Anonymous Coward
    Maybe this is a good way for humans to travel thru space while conserving fuel. Comments?
    • Maybe this is a good way for humans to travel thru space while conserving fuel. Comments?

      You would not conserve fuel, because it takes more fuel to land on a comet than it does to "park" in space nearby.
      In fact, it would be more fuel-efficient to avoid the comet altogether, and just travel toward your ultimate desination.

      That said, there is one scenario where hitching a ride on a comet could be beneficial:
      A spacecraft with an ion engine could rendezvous with a comet to refuel itself.
      However, this is not

  • by questamor (653018) on Saturday January 31, 2004 @06:16PM (#8146657)
    I'm curious. How big does an object have to be to have gravity that'll hold say, a person to it?

    I'm thinking say, if I were standing on a rock the size of NYC out in space, would I just drift away from its surface without any noticeable gravity, or could it hold me there? How about something the size of a state like Oregon? or something only 2miles in diameter?
    • by halftrack (454203) <jonkje @ g mail.com> on Saturday January 31, 2004 @06:35PM (#8146750) Homepage
      It's all about escape velocity. [wikipedia.org] The mass needed to keep a person on an object or in an orbit comes down to the speed the person can obtain by its own force. (Jumping or pushing or something.) Since an object like this is evacuated there is little to slow things down so should the get a little push in a direction, it will have a relatively large impact.

      (And no, I don't care to do the math.)
      • Ok, here's the math (Score:5, Informative)

        by rillian (12328) on Saturday January 31, 2004 @07:38PM (#8147070) Homepage

        As mentioned, you have to be moving slower than the escape velocity [wikipedia.org] to be in orbit around something. The formula is v = sqrt(2GM/r). G is 6.67x10^-11 m^3/s^2kg everywhere.

        For Earth, M is 6x10^24 kg, and the highest relevent velocity as at the surface, so r = 6x10^6 m. That's 11.2 km/s. Very fast. Which is why it's hard just to get into orbit.

        Now for the comet. If it's 4 km across, r = 2000 m. I can't find a value for the mass, but based on the common description of comets as dirty snowballs [seds.org] let's guess the density is about that of water, or 1000 kg/m^3. The volume of a sphere is 4/3 r^3 so our guess for M is 3.35x10^13 kg.

        That makes the escape velocity for 67P/Churyumov-Gerasimenko at 1.5 m/s which pretty much the same brisk walking-speed which which the lander is expected to hit the comet, especially if our guess at the density is high. Thus, the lander could easily bounce off, and a person could with some effort jump off, fast enough that the comet's gravity wouldn't bring them back. On the other hand, an rocky asteroid (denser) the size of Manhattan (bigger) would probably be hard to get away from under your own power. This comet is right on the edge.

    • by kryptkpr (180196) on Saturday January 31, 2004 @06:37PM (#8146761) Homepage
      Fg = G*m1*m2/d^2

      with m1 your mass, m2 the rock's mass, G being 6.67e-11 for our universe and d being the distance between you and the rock.

      So there is ALWAYS gravity, but when you hit an asteroid at 1m/s, your momentums (m1*v1) and the asteroid's momentum (m2*v2) adjust, and propel you and the asteroid in opposite directions because momentum, like energy and forces, is conserved.. and since m2 >> m1, this results in a bouncing off situation (there's a formula for it, but I can't be bothered to break out the notes from first year physics).. The gravitation force between you and the asteroid now has to be enough to counteract this bouncing-off-one-another for you to stay on it.
      • If there is no lost energy ("perfect" bounce), m1*v1+m2*v2 = m1'*v1'+m2'*v2'
        With mX' and vX' the mass and speed after the impact.
        • I'm sorry but the formula you introdused only states that momentum is preserved, not energy. Also your formula true for all collisions, 'perfect' or not, also when kinetic energy isn't preserved. The grandfather is however only vaguely on target when addressing the question of staying inside the gravitational field of a comet. The thing to address is energy, not momentum.
          • You are right. And momentum has not much to do with escape speed. If I remember well, escape speed can be calculated from the enery needed to gain infinite potential energy from the planet/comet or something. G*M*m/d=(mv^2)/2 => v=(2*G*M/d)^(1/2) with G the gravitational constant, M the mass of the planet/comet and d its radius (yes it's a spherical bear :op ). Now from the article, the comet's diameter is 4km and assuming it's mainly water its density should be around 1kg/dm^3. Volume of a sphere is (4*
      • by Anonymous Coward
        Here's the way you'd go about calculating the orbital velocity. This is a Newtonian (in the very essence of the term) question, and can be solved using only forces. The key relation is that for a particle moving in a circular path, the force required to keep it moving in that path is

        F = m v*v / r

        Where m is the object's mass, v is its velocity, and r is its radius. Newton's law of gravitation states that the force exerted upon a mass by another mass is

        F = G m M / r*r

        G being the gravitational constant, m
    • Any two bodies attract and that force is proportional to the inverse of distance squared (and proportional to the product of the masses). A small distance (between the centers of mass of the bodies) implies a huge force. The question is not whether there is enough gravity to hold the object, but what other forces are involved.
    • Its to do with mass and not physical size. The object doesn't have to be big at all - a black hole is a singularity and effectively has no size. Okay, so its event horizon does (this is to do with the distance from the black hole that the escape velocity - how fast you need to move to escape the gravitational pull - exceeds the speed of light).

      A small dense body could have more gravitational pull than a larger, less dense one. Comets are not very dense or large, so have a small gravitational pull.

  • cometing (Score:1, Funny)

    by Alephcat (745478)
    shouldn't this be banned under the international whaleing treaty?
  • by Rosco P. Coltrane (209368) on Saturday January 31, 2004 @06:21PM (#8146684)
    And it will take up to 2014 before landing on Comet 67P/Churyumov-Gerasimenko -- with the help of a harpoon.

    What makes them think they'll be able to land an unmanned probe on a small rock in deep space that way when here on earth, countless bigger, manned ships have tried the same feat on whales for decades and failed?

    They're just gonna kill that poor little comet. For nothing. Just like that. Somebody calls green-piss ferchrissake!
    • "They're just gonna kill that poor little comet. For nothing. Just like that."


      They're not just going to kill it! They're going to study it, torture it, bombard it with microwaves, dig holes in it, and "make an on-the-spot analysis of the composition and structure of the comet's surface and subsurface material" while it's still alive! Now the question is, who do we call about this?
    • Not to put too fine a point on it, but are you not aware that we harpooned the Humpback Whales complete ly out of existance? And nearly did it again, hitting a Bird of Prey with one of those suckers?

      Yeesh.
  • by fname (199759) on Saturday January 31, 2004 @06:25PM (#8146701) Journal
    The French had a very reliable launch vehicle, the Arianne IV, which they decided to "upgrade" with the Arianne V. After failing on 4 of the first 13 missions, they introduced an upgraded version with an extended nozzle. The failure of that launch led to the (highly justified) delay of the Rosetta launch on a similar Arianne V because of the failure investigation. Turns out that the nozzle had a design flaw which led to the failure.

    ESA did pretty well on their 1st trip to Mars, as the Mars Express is an unqualified success, but the Beagle II didn't work for whatever reason. All this is just to reiterate that space is hard, and there will be successes and failures. No one's at 100% (Russians have a worse track record on Mars than anyone, and NASA lost Contour--not a JPL mission-- last year due to an obvious design flaw).

    Whenever a new technique is tried in space for the 1st time, the odds increase. That Pathfinder worked on its first attempt at a bouncy landing, and Sojourner roved Mars without a hitch speaks to the talent & luck of the JPL crew. Hopefully the Europeans will do as well with their harpoon, and hopefully they haven't made obvious mistakes like those made by NASA and the APL did in the Contour comet mission.
    • I'm not sure if you deliberately write it as you pronounce it, but in case you don't: it's "Ariane", not "Arianne". If that is a typo, it's a frequent one. And Ariane is clearly not french. There is substantial french contribution, no doubt -above all the launch site- but Ariane is a European project. I agree with you that Ariane 4 was abandoned with too great a haste- however, that step was inevitable sooner or later. Ariane 5, plus extensions, will be able to carry much larger payloads, and for smaller
    • I was surprised to see you say refer to a NASA mission as non-JPL. What do you mean by this? Isn't JPL is a part of NASA? Also, what about this [nasa.gov]
      • Well, all these aerospace programs have a lot of hands in them. It wasn't a JPL mission in the sense that JPL was not in charge of the system engineering, and they were not in charge of overall mission success-- they had a team that contributed to one part of the mission. The failure of Contour wasn't due to the failure of any one system, but instead was likely due to a component working as designed, but the system engineers did not understand how it would function; working as designed the solid rocket moto
    • Too bad the ESA doesn't have the equivalent of a Titan-Centaur which was capable of sending the Voyagers directly to Jupiter. That would have shaved a few years off the trip. The ultimate would have been a Saturn V with a big-ass Centaur stage to replace the LEM, SM and CM.
  • by Graemee (524726) on Saturday January 31, 2004 @06:48PM (#8146811)
    Too bad they didn't call the craft Ishmael or Ahab.
  • Ishmael?

    Or would Captain Ahab been more appropriate?
  • by Wyatt Earp (1029)
    If /. and Spaceflightnow are still running in 2014, I will look foreward to the coverage
  • I vote we call it YT!
  • by Anonymous Coward
    I initially read this a corset hunter, which piqued my interest.

    Then I remembered I was on Slashdot. News for nerds. Since I'm married, I claim that I'm no longer a nerd, just a plain old geek.

  • Dangerous route (Score:3, Insightful)

    by Limburgher (523006) on Saturday January 31, 2004 @07:16PM (#8146923) Homepage Journal
    I'm just hoping Rosetta survives the trip. I can just picture it getting Beagle-2'd by an asteroid on one of it's 2 trips through the asteroid belt. I mean, I know it's a longshot, but you never know. I hope ESA's luck improves with this one. Thie could be realy cool.
    • Re:Dangerous route (Score:3, Insightful)

      by snake_dad (311844)
      It sounds like you think that ESA has trouble putting together a succesful mission based on the fact that Beagle2 seems to have failed (maybe I'm wrong, but that's the impression that I got from your post)...

      First, Beagle2 was not an ESA project, but that's nitpicking... Second, the "main" part of the European Mars mission, the Mars Express [esa.int], is working flawlessly thusfar, with spectacular imagery sent back already.

      And, there have been many more succesful ESA missions. There have been many more ESA missi [esa.int]

      • I meant no disrespect to the ESA, I merely meant to say that I hope this project succeeds. Wasn't SpaceLab an ESA project? That was a raging success, IIRC.
    • You have a valid concern. I hope that they have designed this spacecraft to tolerate radiation doses far beyond what they expect to see over the course of the next solar cycle (its a 10 year trip!). Remember the Japanese Mars orbiter that eventually failed to enter orbit, largely because it got nuked by coronal mass ejections? During a 10 year trip spanning solar maximum, the Rosetta spacecraft can expect to be hit dead-on by several CME's. The dose -- and the damage -- is cumulative. Let's hope they d
    • Re:Dangerous route (Score:3, Informative)

      by juhaz (110830)
      The asteroid belt is really quite sparse, not at all what most people would expect after watching/reading bit too much scifi.

      Very unlikely that it will even even get to see any of the rocks if it's not intentionally directed to fly by one of the big ones to get pretty pictures, much less get hit by them.
  • Kill it (Score:3, Funny)

    by mnmn (145599) on Saturday January 31, 2004 @07:16PM (#8146924) Homepage
    So after the lander fires a harpoon, the rigid comet breaks into hundereds of pieces and a single "oops" by mission control will echo around the Houston room.

    Whats wrong with superglue? Still stuck with the "lets go GET it" thinking?

    Rants aside. I really hope it works, and we get high res public domain pictures of it to make our desktop wallpapers out of.

    I wonder if it would be cheap enough to steer the whole comet towards the earth into an orbit, and just bring it right next to the IIS. Spacewalking astronauts could then harpoon it to their hearts content
  • by aiken_d (127097) <brooks AT tangentry DOT com> on Saturday January 31, 2004 @07:34PM (#8147037) Homepage
    In the absence of significant gravity, won't a significant amount of the force used to launch the harpoon serve to actually propel Rosetta *away* from the asteroid? Can someone explain what's to keep the harpoon from going "boink" against the comet and Rosetta from not just bouncing but actually being propelled into space by the harpoon launch?

    Cheers
    -b
    • Presumably the harpoon will have waaay lower mass than the lander, and the comet waaaay higher mass than either. Low acceleration for the lander = no problem in the time scale we're talking about. High mass (approaches 0 accel.) for the comet means that the harpoon buries itself. I think...
  • by Uncle Barnard's Star (714324) on Saturday January 31, 2004 @07:45PM (#8147111)
    The cool factor is undoubtedly high, kind of like catching a speeding racing car to find out what's under the hood. The risks are high, and the payoff is worth its weight in journal articles. Maybe it's time for missions that try to justify thier cost in kind.

    The so-called great voyages of discovery of the past were never undertaken for the sake of idle science all. Always there was that search for the elusive El Dorado or that secret shortcut to the spice capital of the world. While most voyages failed to recoup the wood and slave labor invested on them, enough returned with if not the silver and gold then things that would prove more valuable, like coffee, cannabis or the claims to a "New" World.

    The pure science mission ("Is there life on Mars?") is a modern invention. While the altruism is admirable, the only way to justify to taxpayers the continued exploration of space is to turn these missions into hunts for precious metals and minerals. Follow not just the water (a valuable space resource in its own right) but also the platinum.

    • I don't think mining ever will be a good reason to explore other planets. After all, we are living on a giant rock, containing enough gold to cover all continents knee-deep. It is just a matter of digging deep enough, which of course is not simple nor cheap, but probably more realistic than mine another planet.

      Today, the most valuable resource we can get from other planets is knowledge. Knowledge is the currency that can be transferred to money, if applied well. For example, finding DNA on Mars would tell
  • "Towards thee I roll, thou all-destroying but unconquering whale; to the last I grapple with thee; from hell's heart I stab at thee; for hate's sake, I spit my last breath at thee. Sink all coffins and hearses to one common pool! and since neither can be mine, let me then tow to pieces, while still chasing thee, though tied to thee, thou damned whale! Thus, I give up the spear!"

    Decade long hunt... Harpoons... Big ass prey...

    I think I've heard this story before
  • ...why don't they shoot the harpoon first and use it to reel the probe in?

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