Paintball Pellets As a Tool To Deflect Asteroids

A reader 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."

Re:Too tenuous

[Dr_Barnowl]

Rockets have *terrible* specific impulse, around 450s for a complex bi-propellant liquid rocket, and 250s for the stable, reliable solid rockets.

Ion engines have specific impulse up in the thousands to tens of thousands of seconds.

Rockets have a lot more thrust per unit of engine mass, but getting enough propellent up there to give an asteroid sufficient delta-V would be all but impossible - for every big-ass rocket, you'd need a 10x bigger assed rocket to get it there in the first place.

We need better tracking first

[runeghost]

We've known that incoming (and outgoing - the Yarkovsky effect) radiation can alter an asteroid's trajectory for ages. But such a solution needs to be implemented far in advance of any pending impact. At present, we don't know the trajectory of potential impactors, like 9942 Apophis, to sufficient precision to make a deflection strategy like this useful. While it's true the odds are exceedingly small, accidentally putting an asteroid into a dangerous orbit would be disastrous. Apollo astronaut Rusty Schweickart proposed putting a tracking beacon on Apophis in order to further refine its orbit, which would allow us to use such gentle deflection strategies as the one outlined in the article. NASA turned him down. Fortunately, the Russians are currently planning a mission to Apophis; so maybe it will end up getting deflected via a generous application of paint.

Re:Why would increasing the albedo...

[slashping]

Increasing the albedo makes the photons bounce back, which requires a bigger change in momentum than just stopping them.