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The Use of Nuclear Explosives To Disrupt or Divert Asteroids

Discussion in 'Science' started by Goth, Nov 29, 2008.

  1. Goth

    Goth Grumpy Member

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    So, one day, some Google employees were sitting around thinking, well, we totally don't want to sit through another seminar on testing Ajax applications, or some shit.

    So, what other subject could we have a talk on? Oh, how about the use of nuclear explosives to disrupt or divert dangerous near-Earth asteroids! That's important, valuable information for Google employees to be briefed on!



    Very interesting stuff.

    What we have here is a nice little review of all aspects of detecting, studying, characterising, tracking and deflecting or destroying potentially dangerous near-Earth objects.

    Certainly, over the last century, since the Tunguska event, and especially over the last 30 years with Alvarez's understanding of the K-T extinction, and the observation of the Shoemaker-Levy 9 collision, the potential for an impact event on the Earth, and what the ramifications of such an event could be, have been taken more seriously.

    Whilst such events have occurred throughout the history of the planet, it is only in our time, over the last 50 years, with our astronomy capabilities, space-based remote sensing, computational physics, spacecraft propulsion and nuclear weapons that we actually have the means to detect, characterise, and if necessary to destroy such an object.
     
  2. daztay

    daztay Member

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    Interesting watch

    Looks like comets are the real worry.
    I did find it amusing painting them white.
    Also the liability problems.
    Would you attempt to nudge one with the risk of changing it impact point from one continent to another?
     
  3. Heatpipe

    Heatpipe Member

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    There is massive problems with this idea ,
    One, the only rocket we have that is powerful enough to reach long distances is the saturn 5. BUT we no longer have the a working rocket as well as NASA threw away the blueprints for them.
    IF you could get a rocket that can get it into space what happens if it fails on the platform or in the atmosphere you'll get a massive problem with radioactive fallout.
    Assuming you get it into space and detonate the payload you risk making 50billion little radioactive bits raining down on earth.
    NOW this all assumes you detect the object before it hits and in enough time to send up a rocket defect it!
     
  4. Whisper

    Whisper Member

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    If a 1KM rock or larger is going to hit the Earth, radioactive fallout is the least of our problems.

    A
    This was addressed in the video.
    Don't travel in a plane if you are concerned by this amount of radiation.

    I was going to say something, but nah. ;)
     
  5. SLATYE

    SLATYE SLATYE, not SLAYTE

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    A myth. NASA has all the blueprints on microfilm. There's an article here explaining this, and why they're not going to be re-building Saturn V any time soon. The main reasons:

    (1) The components have changed. While the plans for the rocket are safe, the specifications for many of the components used in Saturn V are long gone. They'd essentially have to re-design everything other than the basic structure; and there wouldn't be time.

    (2) They can't launch it. NASA's launch facilities can handle Saturn V or the Shuttle. Not both. Obviously when the Shuttle took over, the facilities all got converted to launch that. It'd take many months just to get to the stage where they might be able to launch a Saturn V (if they had a Saturn V to launch).

    A lot of people have asked why NASA isn't just re-building Saturn V rather than designing a new rocket that'll do much the same task. The answer is pretty simple: it's easier to design a new rocket than to re-design the Saturn V using new components. To re-design Saturn V would essentially be designing an entire rocket, but fitting it onto a pre-defined shell (from the Saturn V plans). It's much easier to just design a new rocket and build a new shell to suit that.

    When the alternative is being hit by a rock that's likely to wipe out a substantial proportion of the Earth's population, I'm not too worried about the risk of radiation.
     
  6. Heatpipe

    Heatpipe Member

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    I do like how at 3m/s that objects take on the kinetic energy of high explosives
     
    Last edited: Dec 1, 2008
  7. bonox

    bonox Member

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    metres? or kilometres?

    3m/s can be run fairly easily. 100metre sprint in 10s bloke running into you may knock you out, but he's hardly going to cause the destruction of the whole stadium.
     
  8. Ashpool

    Ashpool Member

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    I figured the go was not to use explosives but do do "early detection" and use an ion thruster to nudge it off course. Slow thrust over time. If you think of a massive supertanker on a straight heading you can push it off that heading with a small amount of lateral thrust. Trick is to be able to detect the roids early enough to do this.

    And as for the issue of time, you would be amazed at what man can do when he needs to. Look at the production of munitions and equipment during the world wars!
     
  9. bonox

    bonox Member

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    it's a trade off problem. THe earlier you find it, the less mass you need to divert it, but the more mass you need to launch the nudge vehicle in the first place.

    And then gravity takes part - if you don't nudge it far enough, you are merely delaying the problem as it will come back again. It may be enough to come up with another solution though.

    Also, moving a cubic kilometre of a dense material requires a non-trivial amount of mass, even with lots of time. And we don't have ion thrusters giving more than millnewtons of thrust yet I believe.

    Once you start to run some numbers over the back of an envelope, the problems are staggering. A single cubic km of rock @ 4tonnes/m^3 is 4E9 tonnes.

    Assuming that the thing would hit earth smack in the middle, you'll have to move it at least 40,000km sideways (ie to avoid taking out all our satellites)

    At 40,000km offset by the time it gets here, you'd need a terminal velocity of 1.2m/s (4E7metres/365daysx24hrsx3600seconds/day) using distance = velocityxtime.

    The constant acceleration required to do this is the terminal velocity^2/(2 x distance) = 1.2^2/(2x40,000) = 1.8E-5m.s^-2.

    Which seems trivially small. Until you look at the mass involved.

    using F=ma, you'll need a thrust force of 1.8E-5m.s^-2 x 4E12kg = 7.2E7N

    Since a single J2 engine from a saturn 5 is an order lower than that, you'd need a pair of saturn 5 rockets, burning continuously for a year to move a single cubic km rock off to the side.

    And if the asteroid is bigger? Or you need more time to actually build a rocket and get it out there in the first place?

    Can you see the problems starting to build?


    And "what man can achieve when he has to" doesn't really take account of completely depleting a planet to find enough material to achieve such a feat.
     
  10. bonox

    bonox Member

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    I guess all i'm trying to say is that if there really is a planet killer in our future, it'll be an easier task to just move small populations to another planet than to push it sideways.

    Otherwise you need alternatives. Break it apart so the pieces go around earth. Or capture it in a hyperspace field and move it through the earth like stargate.

    Or make it hit another planet instead.

    Or something that doesn't involve just pushing on a bit of rock for long enough.
     
  11. patto

    patto Member

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    Thanks bonox. Saved me alot of typing. :thumbup:

    I didn't watch the 1hr long video but my immediate reaction is that nukes don't provide much thrust anyway.
     
  12. bonox

    bonox Member

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    they wouldn't have to. At least not in the sense you mean. You'd use the mass of the asteroid itself and use the explosive to generate the two halves of an equal and opposite sum of momentums.

    I tiny trickle of water in a rock fissure that turns to ice can split hundred of tonnes of that rock. This is what you would use explosives for.

    The downside is that you can't do it from the outside (ie an 'air'burst), but would need to bury the explosive some distance below the surface. That's the complicated bit, and we don't have the technology to kinetically bury things more than 10 metres below the surface without having them destroyed in the process. Look at the bunker buster or earthquake style weaponry we've developed.

    Your last resort is to dig. And that's going to take a large amount of time
     
  13. WarpSpider74

    WarpSpider74 Member

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    I thought the current line of thinking was not to fragment the 'roid, as bonox seems to be suggesting here. That would likely produce multiple impact risks of smaller size without significantly diverting the trajectory.

    Early detection and response is the key to whatever solution is proposed, as has been said before. A small change early on requires much less effort than a big change at the last minute. Diverting the trajectory by 40,000km (but why stop there?) is not much when you have several AU to work with.

    Recent articles on this subject referred to using a gravity tractor, which seems fairly logical to me.

    Or, we just send out a Hulk and mine that frakker for Kernite. Oh, wait...
     
  14. bonox

    bonox Member

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    yes, that's the point I was making. Breaking an asteroid in half (if it could be done) would send bits around the earth. Unfortunately, because of the problem of being able to set off the explosive deep enough in the material that you had a comparable mass in each chunk, you'll just blast bits off without significantly altering the path of the biggest bit.

    Also, direct pushing doesn't work either, as the energy sum proves.

    So you have to get creative in your solution. I should point out however that you need to think about what has to happen.

    THe energy required is the same. You've still got to move the thing sideways by the same amount. Thus the energy required is the same, whether you do is early or late. What does change with time though is the acceleration required. And the more time you have, the less acceleration (and thus force, or rocket impulse) you need to do the job. THe catch is the smaller the impulse engine, the more detection range you need, and the bigger the rocket you need to get that engine out to the asteroid in the first place.
     
  15. anthony256

    anthony256 Member

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    It's easy, Superman would go up and push it back...
    Done.
     
  16. WarpSpider74

    WarpSpider74 Member

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    Breaking it in half would not necessarily send the halves splitting nicely either side of the Earth. You'd need a MASSIVE amount of force to split the 'roid in the first place, even if there was a convenient faultline. Then you need to overcome the gravitic attraction of the two halves for one and other, otherwise you've just got two big chunks (and a heap of smaller ones) on the same trajectory.

    No it isn't. A 0.005 degree change is much easier to effect than a 0.1 degree change. You're not moving the asteroid literally 40,000km sideways, you're just altering it's path. What you're saying is analogous to telling me that if I make a one degree course change in my boat when I see a tanker approaching me on the horizon, I'm expending the same energy as swerving out of it's way when the bow wave is nearly upon me.

    Oh, and
    Project Orion? Does the name Freeman Dyson ring a bell?
     
  17. bonox

    bonox Member

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    small explosive in a sealed box = big results. Look at a hand grenade. All you have to do is split it and momentum will take care of the rest. As you've noted, time is factor, however the gravitational attraction of a cubic km of material isn't high enough to cause a collapse in a year or ten if you were to split it to pass around the earth. You don't care if it comes together again once it has gone around you.

    The second criteria is that we know the earth can survive atmospheric entry of smaller chunks. ANd this really is a survival step; it doesn't have to be a complete pass.


    angle over travel distance gives you the seperation distance between object and earth. You still have to move it the same distance. If the angle is smaller, the travel distance between the object and earth has to be greater when you start. You still need to shift it sideways the same 40,000km regardless of when you start. Draw up the vector components yourself - ring a bell?

    same condition as the boat. You've still got to move yourself the same distance to the side. Thus, you've still got to input the same energy in the side motion vector, regardless of time involved. Only the accelerations (and thus force or power) changes due to time, not the energy.

    yes it does - how are you proposing to overcome energy limitations based on having to move an object a certain distance? That's where using knowledge of physics comes in with things like the gravity engine type thing - knowledge of sum of momentum >> brute force. Assuming you have the time and technology to implement it of course.
     
  18. Cadbury

    Cadbury Member

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    That does not sound correct. If an object moving at X m/s strikes a much heavier object at an angle of 3 degrees (deflecting the moving object's path by 6 degrees) it will impart far less energy than if it was to strike the same object at 45 degrees (causing a 90 degree course change)
     
  19. bonox

    bonox Member

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    err... que???

    there is no collision involved. Draw the vectors. Regardless of how you come to the conclusion, the length of the vector normal to the original path of travel is always the same length - 40,000km.

    If you are heading straight for the tanker which is 20metres wide. Regardless of when you turn, you still need to move 10 metres to one side. The later you leave it, the greater the acceleration you need to make it within the limited time/distance available. Make the turn sooner and you can be lazy about it. But you still need to cover the same 10 metres, but with a smaller cutoff angle.

    And in terms of moving your boat that 10 metres to one side, the same energy is involved whether you do it fast or slow. Power/acceleration is a rate at which you do something. ie energy per unit time. Total energy is the same.

    Same as climbing stairs. The energy required to move from the ground to the top of a building is mgh. This doesn't change whether you walk slowly or run. What does change is power. More time = less power.

    Different way of looking at it. If you stayed where you were, you would get run over. If you moved 10 metres sideways and let the tanker come to you, it would miss you. What happens in the other vector component doesn't change the fact that you need to move 10 metres sideways. That's the basis of my calculation above. the only thing that time affects is the acceleration you need to impart to the body so that it achieves the required side clearance distance by the time it gets to you.
     
    Last edited: Dec 2, 2008
  20. kingborel

    kingborel Member

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    That's the point. The later it's left, the more energy you will need to change the course enough that it will miss the earth.
     

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