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Deflecting asteroids with paint balls


October 27, 2012

Artist's concept of Apophis being hit with paintballs (Image: MIT)

Artist's concept of Apophis being hit with paintballs (Image: MIT)

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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.

An artist's concept of the asteroid Apophis (Image ESA)

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.

Coating an asteroid with paint would increase its albedo and turn it into a solar sail (Image: MIT)

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

About the Author
David Szondy David Szondy is a freelance writer based in Monroe, Washington. An award-winning playwright, he has contributed to Charged and iQ magazine and is the author of the website Tales of Future Past. All articles by David Szondy

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.


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.

Oliver Medvedik

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.


How ironic would it be if the "paintball" method pushed it into the gravitational keyhole?


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.

Michael Mantion

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.

Victor Engel

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.


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.


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.

Norm Rhett

I think paint balls would merely create a dust cloud as the pellets splat on the surface. Once the dust resettles, the paint will be covered.

The best way to permanently get rid of an asteroid is to decay its orbit into the sun (or Jupiter). I wonder how much of the asteroid's makeup is water or other frozen liquids and gasses. Landing a reactor on the asteroid then melting off the ice could reduce its mass, thus it easier to get pulled into the Sun.


My vote is to gently land and set up a small nuclear reactor on its surface, and then use the heat from the fissioning material to super heat a stream of hydrogen ala the Kiwi rocket program from the 1960s. The velocity of the hydrogen escaping from the rocket engine might provide enough thrust to re-vector the rock into the sun or just out of our solar system at least. Of course this hydrogen gas rocket engine would have to be pretty darn big or run for a really long time to effect much change in the flight path. Or we would have to use a couple of them to get the job done right. The inertia of a rock that big, woooo, it gives me the willies just thinking about it!! We're not talking about deflecting a spit ball here, that's for sure!! Without a real world test of it, there's no way to know for sure if an attempt at painting that rock white would work as hoped. Sherwin Williams may cover the world, but who's going to paint a space rock? The paint balls would have to be heated up to make sure that the paint would be in liquid form when delivered to it. Has he or anyone else for that matter calculated how much paint would be needed and all of the logistics involved there? I doubt it. How big would each of those paint balls be? A couple of liters each and shoot thousands of them? As for thousands of small fragments hitting us, that's much better than one big one! A cloud of small chunks would make a nice meteor shower, where one big one could ruin your whole planet! But too many small ones would take down a goodly portion of our satellite population.


Expanded Viewpoint

So, since we're landing a craft of the asteroid, we might as well anchor it to the surface and use its thrust to push the damn thing into deep space. If solar sails will work so should this and, I'll bet a few thousands gallons of paint and few thousand gallons of fuel aren't appreciably different in mass or volume. Who knows, some other civilization may discover our solution, take exception to our special delivery and let us know their point of view...inter-galactic table tennis.


The Orion drive is the highest-performance interplanetary rocket we've yet designed. While the solar sail approach, cumulative over dozens of years, may work, it's just as likely that a long string of shaped-charge nuclear explosions can provide a staggering amount of thrust. Sure it might cost a ton and reduce our nuclear stockpiles, but the Earth is worth a bundle as it is and reducing our nuclear stockpiles in the name of saving the human race isn't necessarily a bad thing.



Clearly this is not my field, but humor the question.....Why is it not feasible to use the same craft that would fire paintballs, to be designed instead to anchor like a roman candle after delivering it's paint load.? and use the rocket thrust for continual acceleration? It would clearly have more thrust than light on a solar sail alone.


I dub this project the Nelspot Over 9000. ;)

Instead of deflecting NEO's (Near Earth Objects) why not put them into orbit around Earth so they can be mined?

Gregg Eshelman

re; Gregg Eshelman

While technically feasible the capture maneuver takes a lot more energy and the steering tolerance is a lot narrower. for an emergancy deflection it is better to just make it go away. But if you have time land the mining equipment on the asteroid, map, and begin extracting its resources and then capture it the next time it come around.


Good luck getting a phase 1 environmental on this project.

But a couple of points. The rock is rotating, so attaching a rocket to the surface may be a problem except at the poles, assuming the axis would be a good direction for deflection.

And it is powder paint, not liquid paint.

Since Apohis is about 1.5 New Wembleys in size, maybe a burrowing nuke could turn it into powder.

Bruce H. Anderson

re; Bruce H. Anderson

most asteroids rotate on more than one axis. The fastest way of dealing with this is multiple short engine burns with multiple engines, or one exceedingly energetic short burn such as a 100megaton subsurface detonation.

However if you have time you can stop the rotation.


staying focused on the method described in the article wouldnt a more silvery mirror like coating reflect better then a bright white or is it not as intuitive as that ?

Tyson Martel

The rate of rotation isn't given, so we have no idea if a polar landing is needed or not, provided of course that it's just spinning, and not tumbling. If the spin rate is relatively slow, the engine burn time might be short enough to push it in the direction desired before it's going the wrong way. And who knows, maybe this rock IS a remnant from a civilization that blasted a HUGE boulder to smithereens many eons ago, and it has since drifted into our court to play with??


Expanded Viewpoint

How about simply using gravity tractors, paint and solar sails, then when (if) it gets closer subsurface nukes and reaction engines, and if that fails just throw as much energy as you can at it, nukes, lasers, even conventional explosives, by that point you might as well; even if only for spite value.

Of course, you could just do what Naota did and grab a baseball bat.

Alex Aricci

Depending on the asteroids topography,composition and rotation..I suggest a Titanium mesh net with a ring of small SRBs (solid rocket boosters) attached...a combined "catch + push-pull" motion will determine a more controlled trajectory..perhaps even deflecting the asteroid into the Sun or Jupiter gravity fields for impact termination !

Another option (depending on the asteroids composition and rotation) is a deep penetration (HILTI expansion bolt missile with a swivel head attachment to the tow cable ) anchor bolt attached to a towing cable, using a series of controlled burn gas thrusters to change the trajectory. A solar sail attachment to the cable is another option.


Giga- is about 99% less fitting than megatons in this case.

Andrej Radoš
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