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Space Science

Tilting at Asteroids 37

Posted by michael from the f-equals-ma dept.
JimPooley writes "The European Space Agency are conducting a feasibility study into a future mission to knock an asteroid off course. A Spanish company are planning the 'Don Quixote' mission to launch a pair of spacecraft at an asteroid. One hits the asteroid, while the other monitors it to see what happens."
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Tilting at Asteroids More

Tilting at Asteroids

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  • Cheaper, easier and (Score:3, Interesting)

    by PhysicsGenius ( 565228 ) <physics_seeker AT yahoo DOT com> on Friday August 09, 2002 @11:22AM (#4039953)
    more accurate to paint them white [spacedaily.com] and let the sun do the work.

    • Re:Cheaper, easier and (Score:2, Insightful)

      by Xilman ( 191715 )
      More accurate, perhaps, but not as much fun.#

      To be serious: I'm not convinced its either cheaper or easier. If the impactor is nothing but a solid lump of metal with some terminal guidance on board that is going to be a lot cheaper and simpler than a robot big enough and smart enough to paint several square kilometers of asteroid surface. Admittedly, the observation probe has to be smarter and so more expensive.

      What is not clear to me is why the observer has to hang around for so long and so far away. Why can't it just carry a radio beacon and hard-land on the asteroid after waiting for the impactor's immediate effects to dissipate. Thereafter the asteroid's position and velocity could be determined from earth-based observations with very high accuracy and for decades afterwards. That's pretty much what we're doing with the old Pioneer and Voyager probes.

      Paul

      • Xilman writes:

        To be serious: I'm not convinced its either cheaper or easier. If the impactor is nothing but a solid lump of metal with some terminal guidance on board that is going to be a lot cheaper and simpler than
        a robot big enough and smart enough to paint several square kilometers of asteroid surface. Admittedly, the observation probe has to be smarter and so more expensive.

        The impactor could be flimsy drums of titanium oxide powder, with some terminal guidance on board and a self-destruct charge. A few hours before the probe hits the asteroid, ground control detonates the probe and turns it into a big cloud of white dust. This keeps going and hits the asteroid, coating the surface with reflective pigment.

        >:K

      • I agree fully on your point. Being that we might as well start tagging asteroids with our 'extra' satillites and probes. This would help with tracking the asteriod, and who knows, some day it just might be on a course for Earth, but with the tag we'd know exactly what its doing and if we'd need to do anything about the impending doom.
  • Yeah, this is a really good idea. Let's push at an asteroid and see what happens. Plus, if the first satellite pushes the asteroid into a collision with earth, the second satellite can let us know... really fast... and, uh... take pictures of it!

    Yeah! That's the ticket.

  • What if they knock the asteroid into earths orbit? I'm all for this still I'm just wondering...

  • Same Thing we do Every Night (Score:3, Interesting)

    by medcalf ( 68293 ) on Friday August 09, 2002 @11:39AM (#4040061) Homepage
    Hidalgo and Sancho? Is anyone else humming "Mouse of La Mancha"?
  • This is worthwhile because the Earth gets hit by a giant asteriod a few times every hundred million years. If that asteroid is on a collision course with Earth in 2017 (which is unlikely), it would be good because we would have to use up our nuclear missles destroying it.

    Come on, we face real dangers. We are far more likely to be killed by global warming or biological/nuclear/(fill in the blank) war. People are in such denial over these real threats that we do nothing about them; and then we spend lots of money on obscure unlikely threats. Either that or we build bigger militaries because hositility is kind of threat that are primitive brains are designed to deal with.

    • Re:This is worthwhile (Score:1, Informative)

      by Anonymous Coward

      Our nuclear missles won't even make it out of orbit. They aren't designed to go flying off into space to intercept a rock. We'd have to put warheads on entirely different rockets in order to do that.

      • I very much agree, besides what ever happend to that nuclear treaty that was signed a while back that stated the nuclear weapons are not allowed to be detonated in the air, in space, or underwater. I dont remember what it was called but if anyone does please reply with the name.

    • Re:This is worthwhile (Score:1, Insightful)

      by Anonymous Coward
      Just because there are other dangers, it doesn't mean we should ignore this one. There is no regular interval for asteroid impacts. It could happen at any time. I'd be rather pissed if NASA listened to dipshits like you and wasn't prepared when there is a real asteroid threat identified.
    • The danger is there. The indefinite survival of the species requires dealing with it sometime. Yes, climate change, warfare, disease (AIDS, cancer, et al) are all threats to the survival of our species. So is asteroid impact. We don't know how immediate any of them are, so we had better get planning. Just because something doesn't happen often doesn't mean it won't happen soon.

      500-Year floods happen about once every 500 years, right? Doesn't mean it didn't happen in 1993. "A few times every hundred million years" could mean tomorrow. Sky surveys are great, but they don't have the whole sky covered, nor will they in the near future. To quote a popular space-opera, "it's a big-ass sky."
      • 500-Year floods happen about once every 500 years, right?


        No, they happen much more frequently now due to global warming. Consider this a reply to every one who replied to me. What I am trying to say is the time and money we devote to a problem should be roughly proportunate to the size of the danger times the probablity of it occuring.


        I stand corrected on what I said about nuclear missles but this is still a small risk and we are faced with bigger ones.


        I think I'm reacting not just to this article but a general obsession about what happens if an asteroid which is totally disproportunate to actual risk. ..Not to mention that bad movie with that bad Aeorsmith song.

        • What I am trying to say is the time and money we devote to a problem should be roughly proportunate to the size of the danger times the probablity of it occuring.

          Okay. size_of_danger * probability, you say.

          Now, in the case of an asteroid impact which can eliminate many species (all 'big' animals and plants), I'd say size_of_danger approaches infinity. If a big enough rock hits us with enough speed etc., we're all toast. Not just a couple hundred people in some backwater place. All of us. Even if the probability is extremely low, it is not zero. It's happened before, several times.

          infinity * really_small_number == infinity

          That's why people think it's a priority.

          • Same calculation for global warming,
            infinity*bigger number than the one for an asteroid == worry about that first

            Keep in mind that we have limited resourses but we could probably think of causes of extinction until the cows come home. For example, bad guys could turn ebola into a powerful biological weapon, aliens could kill us all, we could get hit by a black hole, etc.

            • Why do you think global warming will wipe us all out? I think it'll be bad for global biological diversity, i.e. many species will go extinct, but it won't wipe out most of the life on earth. It'll just make the earth a less interesting place :-/
              • It is more likely to wipe us out than an asteroid. The envoirnment is so complex that we do not know what will happen if we reduce biodiversity. It is very likely that global warming will lead to massive flooding which will cause soil errosion which will destroy agriculture which will lead to mass starvation.

                Actually, the largest mass extinction on Earth was caused by global warming at the end of the Permian era.

                Make no mistake, any significant change in the envoirnment would be at least a big problem for us and could wipe us out. If it is just a problem then it could still lead to war. A serious modern war could also easily wipe us out.

  • Kicking it off course by a few mm takes 1000 years (Score:4, Insightful)

    by geoswan ( 316494 ) on Friday August 09, 2002 @01:41PM (#4041080) Journal
    ...If all goes to plan, the asteroid's orbit will be disturbed in the beginning by a few fractions of a millimetre...

    I did some of the math for this, on the back of an envelope, when we were this asteroid story from late July [slashdot.org].

    That asteroid was thought to have something like one chance in 300,000 of hitting the Earth in 16 years. I chose 10 years as the amount of time it would take to get something out there to divert it. I assumed it was headed straight at the Earth's center. Then I asked myself how much of a nudge we would have to give the asteroid so it would no longer hit the Earth?

    If an asteroid were headed right towards the Earth, we would have to give ti a big enough nudge to change its target by d-day by something like 5,000 kilometres. That is 5*10^9 millimetres. So if gave an asteroid that was going to hit Earth a nudge of one millimetre per second at right angles to its current trajectory, wouldn't it take at least 5*10^9 seconds to change a direct hit to a near miss?

    There are only 3.1*10^7 seconds in a year.

    So a course change of 1 mm per second will protect us if we have something like 150 years lead time. But adding in a safety margin, and considering they only plan to divert the asteroid fractions of a mm, then that sounds like at least 1000 years.

    • This is only a test run. I imagine that if we were to actualy try to save the planet, we would hit it with a MUCH bigger satalite, moving MUCH faster. And paint it white. And maybe hit it with some nukes. Add it all up, and you'll get more than just that
      • This is only a test run. I imagine that if we were to actualy try to save the planet, we would hit it with a MUCH bigger satalite, moving MUCH faster. And paint it white. And maybe hit it with some nukes. Add it all up, and you'll get more than just that.

        Sure, it would make sense to give an Earth striking asteroid every thing we have got. But the goldarn BBC article didn't say which asteroid they were planning to use as a target. 2002 NT7 is 2 kilometres in diameter. There was an earlier asteroid to hit the news a couple of months ago which was something like 200 meters in diameter. Since the volume, and hence the mass would differ by the cube of the difference in radius, diverting the first one would require 1/1000ths as big a nudge as the larger one.

        I'd like to know how large the target of this mission is.

    • Oh yeah, some slashdotters were suggesting that if we were going to go to the trouble of diverting an asteroid, like 2002 NT7, so it didn't hit us, why didn't we go all the way, and divert it enough to capture it in a useful low earth orbit?

      The simple answer is that would be a cost a lot more energy. 2002 NT7 would have hit Earth with a velocity of 28 km per second. Earth's escape velocity is 11 km per second. To divert it so it wouldn't hit earth required changing its velocity by something like 28 centimeters per second. Capturing it in LEO would require changing its velocity by close to 28 kilometers per second.

      Those velocities differ by a factor of 10^5.

      Now maybe my Physics is really rusty, but the formula for kinetic energy is one half mass times the square of the velocity. So, unless my physics is rusty, the energy to capture 2002 NT7 would be 10^10 times greater than just diverting it.

      If we really needed a big pile of rock in LEO wouldn't we be better off just quarrying the moon?

      • Re:Costs of Asteroid diversion (Score:1, Insightful)

        by Anonymous Coward
        Quarry an asteroid, and use large solar powered mass drivers to throw material off the asteroid at very high velocity.

        This would allow you to slow down the asteroid gradually, and with time perhaps put it into earth orbit. (Who said it had to be LEO?)

        Patience might come into play, but I wouldn't mind a 40 year mission to capture an asteroid.
    • Don't forget there are other forces in play. IE: gravity. If you slow down an orbiting object, it will shrink it's orbit. If you speed an object up, it will expand it's orbit.
      In this way, other modifications may be made to the trajectory of the object.
    • Orbital mechanics are funny. In an ideal system (no light effects, just straight Newtonian gravity and no external effects), if you go up to a satellite in some orbit and give it some sort of instaneous whack with a stick, the effect is to put the satellite into a new orbit. This orbit will intersect with the old orbit in two places, one where you whacked it and one somewhere else.

      Point? If you just change the orbit a little, you don't get anything like a multiplication that you do to estimate how different the satellite's location over time will be then it would have been. In fact you get an oscillation, which with a low enough amplitude will still hit the Earth.

      You really want to exert some force over time to change the actual course of the asteroid. I think that's how the painting the asteroid idea comes into play; it changes the dynamic of the applied forces on the asteroid and can have a real effect on where it will be in the future.
    • I did some of the math for this, on the back of an envelope

      why does everyone always do calculations on the backs of envelopes? It doesn't seem to be the right tool for the job. I always do mine on notebook paper, or printer paper if I can't find any. I occasionally do a short calculation in my textbook or completely on my computer. I don't know I'm strange. I hear Einstein liked to do calculations on the backs of envelopes. If he did it maybe there's something to it.

      Writing of which, did you use classical mechanics or relevitistic mechanics for your calculation? I didn't check your calculation because I prefer to read my own writing over actual thinking. (Besides I can't find an envelope.) It might not matter anyway.

  • In other news... (Score:3, Funny)

    by Snafoo ( 38566 ) on Friday August 09, 2002 @01:57PM (#4041200) Homepage
    The European Space Agency has discovered that, when hit with a space ship at a high velocity, the asteroid can slow and be sucked into the gravity well of a nearby planet.

    You have three minutes to call your parents one last time. Don't die lonely.

  • I had an interesting thought. If an asteroid was to hit the Earth, what would the government do? Tell everyone, and have them all panic? Or launch a secret mission to try to divert it? I'd guess the latter. Anyway, a mission to change the course of an asteroid is extremely hard to hide. So why not just say that it's a "test run"?
    • It's only through spreading panic that governements retain their illusion of relevance. The worst of them manage to panic us sufficiently about drugs, illegal immigrants, sex, terrorists, corruption, hackers, disease and the purported untrustworthiness of our fellow man that enough turn out to vote to maintain some appearance of legitimacy to their exercise of the military, taxation and diplomatic privileges of statehood. What better than an asteroid heading for earth to ensure a star wars candidate gets reelected?

      More practically, there is another significant scientific question which might be resolved by giving a nudge to an asteroid. Right now Newton's gravitational constant is only known to an accuracy of 0.15% which is worse than crude compared to other important physical constants. The problem is basically that it's hard to measure precisely between objects on the earth's surface and we only have crude estimates of the weights of planets, etc. However if we were able to impart an accurately measured and large enough impulse to an asteroid which has its own satelite, with precise tracking before and after, it might just enable us to improve that accuracy by some orders of magnitude.

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