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Space Science

Paintball Pellets As a Tool To Deflect Asteroids 153

SternisheFan sends this quote from an article at MIT's Technology Review: "In the event that a giant asteroid is headed toward Earth, you’d better hope that it’s blindingly white. A pale asteroid would reflect sunlight — and over time, this bouncing of photons off its surface could create enough of a force to push the asteroid off its course. How might one encourage such a deflection? The answer, according to an MIT graduate student: with a volley or two of space-launched paintballs. Sung Wook Paek, a graduate student in MIT’s Department of Aeronautics and Astronautics, says if timed just right, pellets full of paint powder, launched in two rounds from a spacecraft at relatively close distance, would cover the front and back of an asteroid, more than doubling its reflectivity, or albedo. The initial force from the pellets would bump an asteroid off course; over time, the sun’s photons would deflect the asteroid even more."
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Paintball Pellets As a Tool To Deflect Asteroids

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  • Re:Why worry (Score:3, Interesting)

    by slashping ( 2674483 ) on Saturday October 27, 2012 @05:16PM (#41792195)
    It would take a huge asteroid to wipe out the entire human race. We're talking once every 100 million years, or so. Before we spend any resources on detecting and deflecting asteroids, let's wait another 1000 years. On the scale of large asteroid impacts, a 1000 year delay is insignificant, but on the scale of human civilization, 1000 years is huge. If our civilization is much more advanced in 1000 years, we don't need our dated asteroid impact plans. If civilization crashes, our plans will be useless anyway.
  • Re:Too tenuous (Score:5, Interesting)

    by Dekker3D ( 989692 ) on Saturday October 27, 2012 @05:56PM (#41792455)

    You could avoid half the delta-V by not slowing down-... just have the rocket speed up to max speed and slam into the asteroid. Calculate the engine size and fuel amount to be okay for the range you need it at, then make a few rockets to stand ready for various ranges. Crumple zones would let all the impact go into pushing, rather than shattering the thing. Even use some kind of internal room full of tiny airbags if you must. One-way valves (with a tiny air-hole for letting them deflate on impact and not burst prematurely) on all of them, inflate them the usual way or use a small amount of rocket exhaust that you cool down somehow. Simple, really.

  • by symbolset ( 646467 ) * on Sunday October 28, 2012 @12:18AM (#41794495) Journal

    ...change the number of photons impinging on the asteroid, or increase their effect?

    A photon has energy. When a mass absorbs a photon's energy it has two effects: the mass increases in temperature equal to the energy of the photon, and the mass is accelerated in the direction of the photon's path equal to the energy of the photon. This seems like we're using the photon's energy twice, but it isn't so because thermal energy of a mass is kinetic energy shifted into the time domain. All objects in the solar system suffer this "solar wind" effect. The closer they are to the sun the more its radiated photons push them away. Obviously, the sun is emitting a LOT of photons.

    When the mass radiates the photon again it cools and is thrust again in the direction opposite the direction of the escaping photon. Depending on the rotation of the mass and the average time a photon is held before being emitted again (albedo), this can impact the course of the object. By changing the time factor you can cool the object and impact its trajectory. This is called the Yarkovsky effect []. Dark or fast-spinning objects hold the photon's energy for so long that they are radiated in directions that are relatively random and have zero impact on course but they are hotter. Bright objects have more measurable impacts on course because the energy is released in a predictable direction that is relative to the input a vector related to the object's direction of spin but they are cooler. Believe it or not, you can use colors of paint to impact the period between absorption and emission, and use that to align the thrust opposite to the objects orbit around the sun, or in synergy with it. Our understanding of this effect has grown so great that we can tell an asteroid's mass, density, axis and rate of spin based only on its temperature and changes in its course.

    Derivatives of this feature are helpful in explaining the normal expansion of the universe (not inflation), as photons push masses on each end away. When we observe some galaxy 12 billion light years away, we're absorbing its photons and it's pushing on us ever so slightly.

    The difference can be illuminating. Radio Shack and others used to sell a heliotrope device that was a fan with reflectors on one side of the fins and black on the other. The relative difference in albedo would cause the fan to spin in any normal light.

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