Space

# Deflecting asteroids with paint balls

Artist's concept of Apophis being hit with paintballs (Image: MIT)
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An artist's concept of the asteroid Apophis (Image ESA)
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Artist's concept of Apophis being hit with paintballs (Image: MIT)
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Coating an asteroid with paint would increase its albedo and turn it into a solar sail (Image: MIT)

How do you deflect a civilization-destroying asteroid that's heading straight for Earth? Shoot paintballs at it. This may sound like an exercise in futility, but if the calculations of Sung Wook Paek are correct, then the sport of running around in the woods shooting splotches of paint at people on the weekends could get a lot more respect.

Paek, a graduate student in MIT’s Department of Aeronautics and Astronautics, was the winner of the 2012 Move an Asteroid Technical Paper Competition, sponsored by the United Nations’ Space Generation Advisory Council. The contest’s purpose was to find ideas for deflecting an asteroid or other near-Earth objects and Paek’s submission joins a growing list of asteroid-fighting solutions ranging from nuclear warheads to gravity tractors.

Pushing asteroids away before they hit the Earth is more than the plot of science fiction thrillers. It’s a very real threat that may have caused the dinosaurs to go extinct 65 million years ago and astronomers regularly track asteroids that could hit us.

One of these is Apophis – a chunk of rock 1,480 feet (451.1 m) in diameter and weighing 27 gigatons. It’s scheduled to pass near the Earth in 2029 when there is a very small chance that it might go through a “gravitational keyhole.” That is, a spot about a half-mile wide where gravitational forces would send it on a collision course with Earth when it returns in 2036. Apophis is the asteroid that Paek used for his calculations.

The idea is remarkably simple. Paek proposes to send a spacecraft to Apophis. Once on station, it would fire two volleys of paintballs at the asteroid weighing a total of five tons (4.5 tonnes). The first volley would strike the front of Apophis and as the asteroid rotated the second volley would hit the back side.

Being hit with five tons of paint would shift Apophis very slightly, but that’s not the point. That’s because the paintballs would coat the asteroid with a five-micrometer-thick layer of paint powder, which would double its albedo or reflectivity. This would effectively turn the entire asteroid into a gigantic solar sail.

Solar sails are a form of propulsion that are exactly what it says on the box. They’re sails that use the Sun instead of wind to push them along. Sunlight landing on a spacecraft may not seem to exert much pressure, but in the frictionless void of space it can be surprisingly powerful. It’s been known to move geosynchronous satellites, and NASA’s Messenger space probe uses solar sailing as part of its attitude control.

Usually, designs for solar sails involve gossamer-like sails made out of mylar spread out over a huge area. Paek’s idea is to make an asteroid reflective enough that its surface does the job of a sail to push it using the pressure of solar radiation. To an observer, the effect would be as imperceptible as watching the hour hand of a clock move, but over a period of 20 years the solar radiation could push Apophis off its trajectory.

It’s a novel and very simple approach with the added bonus of not having to watch Bruce Willis outrun an atomic explosion.

The video below outlines the paintball deflection plan.

Source: MIT

Deflecting an asteroid, with paintballs

Pikeman
While such a little push might work there is too much to go wrong. I prefer the single high yield event of a ground penetrating warhead with a very high yield.
Oliver Medvedik
I'm not a physicist or geologist (a biologist actually), but from what I've read so far, the gentle nudge approach, started in advance, is the best way to do it. By contrast, an explosive device meant to shatter the asteroid would be far worse, leading to multiple large meteors raining down on the earth.
Pikeman
re; Oliver Medvedik The penetrator nuke is not intended to shatter the asteroid it is to add reaction mass to the push on the asteroid but if you shatter the asteroid all the pieces have been accelerated onto different courses; was not this the plan from the start.
Rt1583
How ironic would it be if the "paintball" method pushed it into the gravitational keyhole?
Michael Mantion
Sounds overcomplicated and retarded. Who's to say that the paint would stick, "dry" or not pick up dull space dust. A large meteor would have a small gravitational force and would have a haze of find dust and debris around it. the object would most likely be spinning and of course moving. Even Also the paintballs could be to hard from the cold or heat up too much in the sun, the release or firing mechanism would be the obvious point of failure. Targeting would also be tough. The solution that most experts have agreed on is the one stated correctly by Pikeman. You use explosive to break off a chunk of the rock and thus push the large mass.
Victor Engel
When I saw the article title, I imagined a completely different scenario. In the scenario I imagined, the momentum of the paintballs would be added to the momentum of the asteroid. In the scenario described, it looks like that momentum is proposed to be effectively neutralized prior to arrival with relatively slow speed paintballs not significantly affecting the momentum.
Rigby5
Explosions don't work. Nuclear explosions are too fast to be able to effect the huge mass, inertia, and kinetic energy. Breaking off a chuck will not change the trajectory of either chunk. If you are going to try something, this is much better than nuclear explosives. But the best is to attach mass thrusters that dig into the asteroid and accelerate and eject reaction material. That is much more expensive however, but has the advantage of being possible to control over time.
Slowburn
re; Rigby5 A rocket is a device throws off mass in one direction to accelerate other mass in the opposite direction. If you use an above surface detonation the only reaction mass you have is the device used and any mass you vaporized from the surface and much of this is wasted by being allowed to expand indirections that do not push the mass you are trying to move. This is why it is optimal to use a subsurface detonation in which everything thrown out of the crater including still solid rock is reaction mass in a short lived but very powerful rocket burn. Your best is exactly what a subsurface detonation nuke does.
Norm Rhett
As I calculate it, the gravitational force, though small, would be enough to grab any matter (paint) within 100 meters of the surface in a minute or so. Adhesion might be a problem, but there would be plenty of time for multiple applications to get it right. If it is required to prevent disaster and does so, the value would clearly be immeasurable.