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Air Bags for Planetary Defense

Posted by michael on Fri Aug 30, 2002 10:15 PM
from the seat-belts-and-infant-seats-also-available dept.
Space
Gallowglass writes "The Canadian paper, the National Post, is reporting on a plan to divert asteroids headed towards Earth. According to the story, the proposer, a Dr. Hermann Burchard, suggests deploying an inflatable mylar bag a few kilometers in size, and using it to push the projectile aside. An air bag for earth? The deployment mechanism isn't detailed in the story."
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  • So that's why Chretien's retiring.

  • Further research..... (Score:3, Funny)

    by Anonymous Coward on Friday August 30 2002, @10:18PM (#4174870)
    ...shows that smaller asteroids may experience neck injuries or even death from the fast deploying air-bags.
  • So if this air bag hit the asteroid - the misery weight of that air bag against asteroid weight send that air bag with all constructions in it flying with very high speed, while asteroid will fly with almost unchanged path...

    --
    Newton laws are guarded by Newton Police
    (City of Newton, KS)...
    • The article wasn't clear on how the air bag will apply pressure to the asteroid. Maybe a slow, controlled leak?

    • Re:Nobody abolished Newton's laws... (Score:5, Informative)

      by darkwiz (114416) on Friday August 30 2002, @10:27PM (#4174903)
      I think the idea would be to make some attempt to match it's speed, then contact and start the engines firing to push it off course.

      Rather than think of it like a car's air bag, think about it as a way to spread out the pressure along the surface of the object. A rocket on the surface of a comet or loosely bound asteroid may just disintegrate the parts, yielding little benefit.

      Which is more comfortable to sleep on: a pillow or the blunt end of a pencil?
    • I think the idea is to catch it far enough away that an "almost unchanged" path is changed just enough to miss the earth. After all <obAdamsQuote>You may think it's a long way down the street to the chemist's, but that's peanuts to space</obAdamsQuote> - the earth is actually a pretty small target, and a relatively small deflection, applied far enough out, would be enough to make a potentially deadly rock go whizzing right by.
  • If the asteroid is small enough you could even use the airbag to skip it off the atmosphere. I have a hard time envisioning some airbag attached to a rocket motor doing much to a larger one in time.
  • Does this mean children under the age of twelve shouldn't be allowed in the front seat of planet earth?
  • to try and figure out how an airbag is supposed to do anything to deflect an asteroid. I eventually inferred that the airbag is like a catcher's mit, connected to huge rockets.

    The article could have been titled, "Huge rockets could deflect an asteroid" ....duh.

    I think I would still prefer nukes....they're just so much more macho.
    • I once did some back-of-the-envelope calculations about deflecting asteroids with a physicist friend of mine.

      Our presumed target was a 1 mile dinosaur killer that is about to hit Earth in a few months and we want to impart enough kinetic energy to change its trajectory so that by the time it reaches Earth it will miss it by a few thousand miles of safety margin.

      Well, it turns out that it takes so much energy that even the biggest thermonuclear devices barely have enough energy to do it, even assuming we could convert it efficiently to kinetic energy.

      A nuke going off in space is just a big flash. No real blast. You need some working mass to convert it to kinetic energy. Using the mass of the asteroid itself is dangerous because you don't want it to break into multiple fragments.

      Here our calculations probably become much less accurate because we took some shortcuts and made some assumptions that may be way off, but the result we got is that we needed to send some tens of thousands of tonnes of working mass (e.g. water) along with the nuke to convert its energy to momentum with reasonable efficiency.

      Needless to say, this is beyond our current launching capabilities.
  • Using the word "Airbag" for this idea definitely gives people the wrong idea. An airbag is used usually to reduce the impact of a fast moving object. In the case it is used as a deflection mechanism. Perhaps the word deflection ballon would be a better combination word?

    Just a thought.

  • Easily misunderstood (Score:4, Insightful)

    by El (94934) on Friday August 30 2002, @10:33PM (#4174928)
    The problem the author is trying to solve is: How do you get a grip on an asteroid for long enough for your rocket motors to change it's path without causing the asteroid to break up. He's suggesting using a giant pillow between engine and asteroid to destribute the force.

    This is the wrong problem, in my opion; he assumes you've got massive amount of rocket fuel to wast. What we really need to do is figure out how to take some of the mass of the asteroid and accelerate it, using this as the reactant to change the path. Sort of like installing a rail gun on the asteroid, and firing off bits of asteriod like b-b's to get the asteroid to move in the opposite direction.

    • What we really need to do is figure out how to take some of the mass of the asteroid and accelerate it, using this as the reactant to change the path. Sort of like installing a rail gun on the asteroid, and firing off bits of asteriod like b-b's to get the asteroid to move in the opposite direction.

      Or haul a bigarsed ion drive over to it, and use charged silica vapour as the reaction mass. Bring spare ionization screens...

      I'm still in the "nuke it" camp, myself.
    • Isn't that really the same problem? If you are bringing your own power, in whatever form, you have a finite amount of energy you can expend in whatever combination you want to change the momentum of the asteroid. Your solution sounds slightly better because after the first shot, the remaining asteroid would have ever so-slightly less mass. But when you consider the problem of mounting a rail gun on some asteroid in a stable fashion...well, the combination of rockets and the super-pillow sounds a lot easier, which counts for a lot when you are a million miles from the nearest astro-workshop and the clock is ticking.

      Of course if you can use external sources of energy, like solar energy (i.e. the solar sail) or asteroid itself, then you really solve one problem. But whatever your solution, if it is really to solve the problem, it also needs to have a rate of work sufficient to deflect the trajectory in the time you have remaining. If the asteroid is big enough to matter, let's hope we have lots of leadtime.
      • Why not just shatter the asteroid? Seems like that would take less energy than either your or his sugesstion. Let the atmosphere do the work, just break it up is chunks that are small enough to ablate down to non-threatning pieces.

        The problem is that most asteroids large enough to be a problem would cause serious problems even raining down into the atmosphere as gravel. Large volcanic eruptions mess up our climate quite nicely; vapourizing a few billion tonnes of rock on re-entry would have much the same effect.

        What you really have to do is fragment the asteroid with enough force that the pieces all have local escape velocity [from the asteroid], and do it far enough back in its orbit that most of the pieces miss Earth [the hard part, as we'd need months to years of advance notice].

        This is still probably the most practical way of dealing with an Earth-threatening asteroid.

      • You have to be really careful about that. Do it wrong, and you send thousands of white-hot rocks down into the middle of California in the middle of July. Oops! Just kindled all the redwood forests.

        If the asteroid is big enough, you could even heat the atmosphere and/or spread enough space dust around to influence the weather in wierd ways. That's not as bad as sending a 1000-foot wave around the Pacific rim, but it's still less than optimal.

        That said, it would be nice if we had enough lead-time to send up something that could pulverize it into little chunks and disperse them widely enough to create a nice annual meteor shower.

        The question you have to ask for all this is: How long would it take us to turn a planet-killer into lots of little pebbles and scatter them widely enough?

        Also, how much energy would that take, and where would it come from? I wager the answer is "a lot" and "from nothing we have right now".

        I think the most practical answer for the time being is going to be "nuke it". Of course that won't turn it into pebbles, but hopefully the chunks will split wide enough to miss us.

        Lead time is everything. We really need as much effort as possible going into detection so we can get as much lead-time as possible. 50 years lead time and we can mine the thing. 5 days lead time and we are the next dinosaurs.

      • Back when "Armageddon" was stinking up theaters nation-wide, I did a calculation in Mathematica using parameters given in the movie, e.g. "Half the distance to the moon," and "the size of Texas," etc., always giving that lovable band of roughnecks the benefit of the doubt and erring in their favor. For example I assumed that the asteroid had the density of water, that splitting the asteriod cost no energy, but separating the halves would require them to escape each other's gravity and just barely miss the Earth.

        If I remember right, the feat they achieved would require the nuclear device they implanted to yield well over 10^40 Joules. More advance notice would lower this number greatly.

  • Moon (Score:2, Funny)

    by suss (158993)
    ...but will the Moon get a passenger airbag?
  • Most asteroids approach at speeds of several kilometers per second. To catch them without popping, the airbag would have to fly out into space, turn around, match speeds with the asteroid, deploy (possibly not in that order) and then fire its rockets the other way to deflect it.

    Wouldn't it be easier just to land on it? Or nuke it?
  • Link [cnn.com] from my rejected story. Grr.
  • All this talk about HOW to deflect an asteriod is wonderful, but I think many people forget that we actually have to SEE the damned thing first. Last I checked we were only monitoring a very, very, very tiny amount of the sky, and NASA's budget is still being attacked by the politicians.

    You can't defend against something that you don't know is there. And I'm also willing to bet that thing thing would take some time to be deployed, so we'd probably need to see the asteriod pretty early.

    Defence plans are great, but what we really need is to be watching more of the sky.
    • How long was it between inital spoting of NY40 and the time it could be seen by a low cost telscope? If it was going to hit, there would have been nothing we could do and some of us wouldn't have a net connection right now. I've personaly been point out to bible thumpers that NY40 might have been a warning from god to prepair and like noah, we can preapir.
  • Goodbye Saddam!
    (just kidding, he's my neighbor)

  • Assuming it's made of air and mylar, it would burst. There is about zero pressure in space. That's why astronauts have to have spacesuits, and those spacesuits are thick and expensive as h3ll. Knowing how relatively weak mylar is, the "air"bag would burst before entered space, due to the immense pressure difference.
  • Movies aside, killer asteroids rank WAY down there on my list of worries. Lets see, what has a better chance of killing me:
    1. Basement Stairs
    2. Lightning
    3. Bees
    4. Falling coconuts (look it up, it really happens)
    5. Brain embolism
    6. CowboyNeal
    • The funny thing is, if you ran this as a /. poll at least 5% of voters would choose the CowboyNeal option.

      On that basis alone, you could argue that CowboyNeal should be permanently incarcerated, as he's demonstrably a menace to society.
  • I can only envision this working if the rock is coming it at an angle. If it is more or less strait on, then deflection would have to be almost 90 degrees. Not very likely.

    Unless, the idea is to push it toward the oceans. But larger asteroids will make a mess for all regardless of where it hits.
    • Unless, the idea is to push it toward the oceans.

      Have you ever throw a rock in a pond? The last place you want an asteroid to hit is in an ocean! Think big waves hitting the shores (which is where most people in the world live.) For a non-trivial, non-planet-killer, you want it to hit in the middle of a big landmass (e.g. middle of the USA, middle of Asia, middle of Australia, etc.) Almost zero population in all those places, still a lot of loss of life, but way less than slapping it down in the middle of the Atlantic or Pacific!

  • Answers previously posted story (Score:4, Funny)

    by mc6809e (214243) on Friday August 30 2002, @11:29PM (#4175091)


    Science: Most Beautiful Experiment in Physics

    Answer: Airbags for Planetary Defence

  • Let's ignore the physics of a 100,000 ton rock hitting a mylar balloon for the moment. I'm more interested in how they're going to get this gas into space. I realize it can be compressed, but 3 cubic kilometers worth? Has anybody done the math here?! The only way I can see this doing a bit of good (and not really even that) is that the asteroid might be nudged off course when the bag ruptures with all it's atmosphere in a shockwave sorta thing. But then, you might as well send 50 nukes up after it... Hell, the engineering there would probably be a lot simpler... I guess, the balloon would have a certain amount elastisity to it before it bursts, giving it some impact resistance as the mylar absorbs the shock, but I have to wonder... Why even bother?
    • All you need is enough gas to apply enough force to the inside of the bag to keep it inflated against the near vacuum of space (oh, and against your rock when you finally hit it).

      eg: a 0.1 psi pressure difference would be more than enough, considering the amount of square inches on the surface of a cubic mile bag. A cubic meter of liquified gas expands to many,many,many cubic meters of gas when you're talking an 0.1psi pressure differential between your container and the Outside.

      Notice my excellent mixture of SI and Imperial units? That's apparently very important and nearly a mandantory requirement in space R&D ;-)
    • I'm more interested in how they're going to get this gas into space. I realize it can be compressed, but 3 cubic kilometers worth?

      There is very little air pressure in space, so you don't need a lot of pressure for the ballon to inflate. You do need to keep enough pressure in it so your rocket doesn't push through the ballon and hit the asteroid. Getting a big rocket to the asteroid is beyond what we could do by next year say. (By "we" I mean Russia since they still have some big rockets, but not that big, it would have to be an international thing with the US sending up supplies, Russia supplying the big fuel tanks and engines, and Europe and Japan footing the bill.)

      One advantage of crashing into this thing with a big airbag before doing a 20-30 second big burn is that the momentum of the rocket would be fully transfered to the comet as more of a translation than a rotation. Plus landing on the comet in a place were it would just translate and not rotate would be difficult.

      It doesn't really rule out the nuclear option either. Since you only get to do that once you'd try this first, then check if you moved it enough. If not an H-Bomb isn't so heavy, you'd have brought one along. Now you just land on the comet and set it off. Hopefully enough of it is vaporized quickly enough to push the remaining fragments off the they collision path to Earth.

      Not that it will matter, we're not looking out the front windshield. Hopefully the first one to hit us in modern times won't be the big one. But I bet if Sydney disappeared one day, we'd arrest all the usual suspects and suspend free-speech immediately. Oh, and maybe do something after the an election cycle, or two.
  • What we need isn't an airbag. What we oughta be doing is building some 5000mph bumpers on top of the Rockies.
  • Is this basically a way to attach a solar sail to an incoming asteroid? That would have to be done well in advance, maybe an orbit or two before impact.

    If you're going to send something to nudge an asteroid, it may as well be an H-bomb. They're small, reliable, and we have lots of them.

  • Air Bags for Planetary Defense

    Yes, I've always thought congress should do something about the risk of asteroids.

    Oh, wait...
  • What happens when the US messes up the asteroid bouncing project and they send the asteroid directly into France?
  • Why use mylar airbags when we've got plenty of used-up old conservatives lying around? Lets' throw Rush Limbaugh out there to protect us from asteroids...
  • Good thing Earth already has a built in air bag, it's called "the atmosphere".

  • Side pocket (Score:3, Funny)

    by Citizen of Earth (569446) on Saturday August 31 2002, @03:12AM (#4175458)
    suggests deploying an inflatable mylar bag a few kilometers in size, and using it to push the projectile aside

    No, what we should do is build a giant pool-cue stick and knock another asteroid into the first asteroid, deflecting it into the side pocket.
  • Not for nothin' but wouldn't the heat of the asteroid (from passing through atmospheric re-entry) smoke a hole in this airbag before it had a chance to absorb much force from it?

    And what would they plan on inflating it with? Part of the protection of an airbag is the force of it inflating as your momentum carries you forward. It's an azide compound that generates a bunch of nitrogen gas that rapidly inflates it. It would be a hell of a chemical reaction to generate enough gas to fill a several km wide cushion. Maybe I should think of it more as one of those airbags the fire dept. uses to keep jumpers from smacking pavement?

  • Tests on Crash Dummies show that Airbags save lives.

    Therefore, an Airbag for the planet earth will save the lives of 6 billion dummies :)

  • 1) F=ma
    2) ????
    3) Profit!

    whats the airbag going to push aginst?

    More great science from Okie State!
    Its sad but I spent some time there till i figured out I could leave....

  • deployment mechanism? (Score:3, Funny)

    by digidave (259925) on Saturday August 31 2002, @10:45AM (#4176404)
    And exactly how do they intend on getting a giant steering wheel into space?

    • Re:Kids, try this at home! (Score:4, Funny)

      by aardvarkjoe (156801) on Friday August 30 2002, @10:37PM (#4174941)
      Mr. idiotnot:

      Thank you for your contribution. Now please prepare a report on why, exactly, incoming asteroids would be hot enough to glow. Be prepared to show whether or not that will be relevant at the time that the plastic hits the asteroid.


      Thank you,

      Your Fifth-Grade science teacher.

      • The moon is 200 degreesF in the sun and -200F in the shade. If the incoming asteroid is facing the sun then it can get up to 200F assuming its not spinning at a fast rate. I do not know how strong mylex is at that maximum temperature but I assume the scientist took this into consideration. I think the previous poster was refering to the tails he see's in commets as they head towards the sun. Of course anything thats water based above 32F is going to create a trail. Its not glowing hot into it gets close to the sun.

        I think the most important issue is how to stop the rock flying towards earth at such an incredible speed. This will not work as a standard catchers mit because it would blow right through it like it wasn't there. However if the asteriod is detected early enough I suppose you could use the ballon utilizing the moon's and earth's gravitation force to closely match the speed of the asteriod and then catch it and slow it down gradually with the rockets or steer its direction. To me that would take a looong time since asteroids can travel up to 28,000 miles per hour and the fastest rockets today can only go up to 7,000 miles per hour. You would have to do many, many revolutions around the Earth and Moon to even get close to the matching speed and then use the rockets to move ahead of the asteroid and then slow it down enough to catch it. It would take years to construct and test this idea. I wonder if it would be cheaper and easier to just send nuclear rockets to detonate at the asteriods surface to steer its course. I am aware it would not destroy the asteroid but steering it may be the only solution with todays technology.

    • Asteroid's are NOT hot. They're out in space, they tend to be a few degrees above absolute zero (ok, so there is some solar heating of the surface). By the time that sucker heats due to friction in the atmosphere, it's WAY to late to deflect it!
    • Nukes would tend to uncontrolably break the object up into smaller pieces; chances are some of these pieces would still strike Earth, even if the original object was going to miss. Granted, I'd rather be hit by a few 100 meter rocks than 1 big 1000 meter rock, but it's still not a satisfactory solution. Now, if you could split the object in a controllable fashion, like a diamond cutter splitting a diamond, it would be useful. Problem is, we know very little about the internal makeup of asteroids, never having been inside one.
    • The idea for doing a calculation like this is

      (Expected Probability of Dying from Impactor of mass M) = (Frequency of impactor of mass M)*(Percent of People expected to Die in Impact)*(Average Human Lifetime)

      For major extinction events (like that which killed the dinosaurs), reasonable numbers are: 1/300,000,000yrs*100%*70yrs = 1/4,300,000.

      So in some sense you have a 1 in 4.3 million chance of dying the way the dinosaurs did.

      Of course that event was rare, but suppose you are a pessimist and think 60 million people (1%) will die from a rock of a size that hits Earth every 50,000 yrs, then this gives a 1 in 70,000 chance of dying in this sort of event.

      The idea is to do a sum over the entire range of impactor sizes with some presumed frequency of impact and percentage of people killed, but because these quantities are highly uncertain, you can essentially claim values that will lead to virtually any result you want.

      In any case, you should realize that the probability of dying by impact is mostly determined by the rate of major impacts, which given 2000 years of recorded history, are probably rare enough that one isn't going to jump on us even if it takes a century to figure what we would do about a asteroid on a collision course.

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