Sounds nice in principle. But can a realistically sized fleet of spacecraft induce enough deflection to head off a potentially hazardous Earth-bound asteroid? The two engineers formulate an answer to this question by looking at an asteroid named 99942 Apophis, which is known to have a trajectory that crosses the Earth’s orbit and has a very small chance of hitting in 2036 or 2037. It’s shaped like a potato, reaching almost 200m (655 feet) along the long axis, and would wreak serious havoc if it hit us.
There are lots of asteroid-deflecting parameters one could vary: the laser power (and consequent solar-cell requirements), the size, number and position of the spacecraft, how they are powered to hold their position, and so on. The craft would have to be actively held in place, not least to counteract the slight push that they will receive from the stuff being blasted off the asteroid. One of the key aims is to find a compromise distance that achieves enough heating without too much clogging of the collector mirrors. The effort any system needs to put in also depends on how much deflection is needed to avoid catastrophe, and how much warning you have: how long you can spend nudging the asteroid, in effect.
All this means that it’s not possible, or indeed meaningful, to say exactly what would be needed in terms of design or cost to get this idea to work. But Vasile and Maddock do manage to establish that if, say, we discovered in ten years time that Apophis really was going to strike, it should be possible to implement a strategy like this based more or less on the technologies already to hand, without any fear of bankrupting the economy. That’s surely a little reassuring, even if it wouldn’t make much of a movie.