Paintball Pellets As a Tool To Deflect Asteroids

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."

Comments

Too tenuous

[hessian]

That's a long shot plan right there.

I think sending Bruce Willis with a thermonuclear device and a boatload of family drama might work even better.

Re:Too tenuous

[Anonymous Coward]

Spaceballs ?

Re:Too tenuous

[Dekker3D]

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.

Re:Too tenuous

[paiute]

That's a long shot plan right there.

I think sending Bruce Willis with a thermonuclear device and a boatload of family drama might work even better.

Modded funny but is actually insightful. What would happen is that the chance of the giant asteroid actually hitting the earth will start out less than certain, so the large expense of sending a mission to deflect it far from earth using a gentle push would result in debate and delay. Then the odds of impact will increase, but the expense of the mission will still be high. We will piss and moan, and a loud minority of self-anointed space experts who begin to say that the rock is actually going to miss, that it is all a liberal/conservative/alien conspiracy, that there is really no asteroid, etc. will get a lot of press. Finally the thing will be visible from earth and the shit will hit the fan but by then it will be too late to use mild persuasion, and we will have to send up whoever passes for Bruce Willis with a crapload of nukes. We will blow it into chunks, maybe even into gravel whose kinetic energy strips away the atmosphere.

Probability and magnitude are both relevant

[perpenso]

The chance of getting killed by a car when crossing the road is orders of magnitude larger than the chance of getting killed by an asteroid.

True. However one asteroid can kill all of us, unlike one car.

The probability of an event must be combined with the magnitude of an event when assessing the risk.

Re:Why worry

[tnk1]

Your point is valid, except that the problem with estimates like that is while they are useful for estimating the risk, they don't say much about whether an asteroid of the required size is actually on its way. In other words, we don't get a do-over if the rock shows up earlier than we thought it would. Not to mention that rocks of the necessary size could be generated by the effects of a collision with another body which then suddenly expels a rock on a collision course with Earth. In that situation, we may well not see it coming until just before the window in which we need to take action to deflect it.

Existential threats like asteroid impacts are situations that you start planning to deal with as soon as you have the knowledge to do so. There is really no reason not to, since given the extreme consequences, it doesn't seem particularly absurd to maintain those plans in a constant state of revision. We know that an asteroid of sufficient size is going to hit again. It's only a matter of time. Maybe that time is a million years from now, maybe it's a week from now. I grant that we shouldn't be building an expensive specialized asteroid defense grid or mineshaft shelter/habitats right now, but an actual plan that could be feasible in the event that we end up with an unforeseen visitor is the right thing to do. In this case, scientists realize that it is very easy to miss Earth if you poke at the asteroid just a little bit when it is far enough out. It's a reasonable plan that really should not require that much expenditure to make happen, if required.

Re:Why worry

[Opportunist]

Problem is, the herd thinning would not be done by brains power but by purchasing power. Now imagine an Earth where only managers and bankers will survive. The living will envy the dead.

Re:Why would increasing the albedo...

[symbolset]

...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.