How Diffractive Solar Sails Could Stop a Killer Asteroid at 100 km/s

Asteroids don’t come with a warning label that they might one day hit Earth. While we don’t know of any currently on course to do so, we are finding thousands of new ones each year, and there’s always a potential that one could. We proved a viable technique for dealing with that eventuality - the DART mission successfully moved a small asteroid using a “kinetic impactor” - basically a big rod designed to push the asteroid off its trajectory. But DART had one big flaw - it was traveling in the same direction as the asteroid, and approached it from behind, eventually hitting it with an impactor launched while in orbit around it. That technique might work if we have enough warning, but would require years of orbital mechanical maneuvering to pull off. An alternative, proposed by researchers at Beihang University, is to use a new type of solar sail to deflect a potentially hazardous asteroid by hitting it head on.