Engineering: How to convert an asteroid into a rocket

Films have solved the potential problem of asteroids hurtling towards Earth with nuclear bombs, drilling and deflection.

However, this problem might need to be solved for real as soon as 2029, when the asteroid Apophis will pass close to Earth. Our planet’s gravity may then put it on collision course when it comes back round in 2036.
 
Although the chance of an impact is only 1 in 45,000, developing methods to save us from such near-Earth asteroids (NEAs) is vital, and current proposals simply aren’t up to the job, according to Daniele Fargion from the University of Rome La Sapienza, Italy.
 
Proposals for deflecting NEAs have included blasting them with nuclear explosives, tugging them with nuclear-powered spacecraft or painting them white on one side so that reflected solar energy will nudge the asteroid off course.
 
However, exploding an asteroid could send many fragments Earthbound, and tugging and painting can only push the asteroid a few kilometres off course, said Fargion.
 
An alternative, proposed by Fargion is inspired by the way rockets are propelled forward as they eject mass when burning fuel.

Nuclear powered rockets

He suggests dropping nuclear powered rockets, each tipped with a screw-shaped drill, onto the asteroid from a mother ship, and after latching onto the asteroid’s surface - not easy in almost zero gravity - each ‘screw rocket’ will drill deep into the asteroid, projecting the rocky spoil behind it into space at high speed and pushing the asteroid off course.
 
Fargion’s calculations show that over 10 years, screw rockets could deflect a one-cubic-kilometre asteroid by 30,000 kilometres.
 
“Instead of carrying huge amounts of fuel from Earth to propel the asteroid this large distance, we simply exploit the asteroid’s own material,” he said.
 
Nick Bailey, an expert on asteroid tracking at Southampton University, UK, calls the solution “elegant” but says that many asteroids are made of piles of rubble, not large chunks of rock, and that it will be tough to get screw rockets to latch onto these.

Another difficulty is that the asteroid may well be rotating. To account for this, screw rockets will be fitted with guidance systems, allowing them to track their position and fire only when they are on the right side of the asteroid to push it off collision course.
 
Fargion proposes to test the idea of screw rockets by sending them to the Moon, where they could also be used to dig out underground shelters for human use.

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