Mirrored army to protect Earth

A fleet of satellites carrying large mirrors, flying in close formation, could save the human race from the fate of the dinosaurs, according to space scientists at Glasgow University.

The ‘Mirror Bee’ concept is the best method for deflecting asteroids on a collision course with Earth, explained Massimiliano Vasile of the university’s Space Advanced Research Team (SpaceART).

Asteroid impacts are a real threat, Vasile stressed: far from being science fiction, they have occurred many times. The Tunguska event in 1908 devastated an area the size of London. ‘If a 100m wide asteroid hit the Earth, the result would be the equivalent of 2000 nuclear bombs,’ he said. Moreover, there are hundreds of asteroids whose orbits around the sun cross the Earth’s; a 400m wide asteroid called Apophis is scheduled to come near enough to Earth in 2029 for its orbit to be affected, which could nudge it into a collision course with the planet in 2036.

Vasile and his team have studied nine methods which have been suggested for deflecting asteroids, including crashing a spacecraft into the asteroid; landing on it and activating a rocket or ion drive to push it away; excavating some material from it and ejecting it to create thrust; using gravitational attraction to turn a spacecraft into a form of tug; explode a nuclear bomb near the asteroid; and the mirror bee option. The latter method uses concave mirrors mounted on satellites to focus the sun’s rays onto the asteroid and heat its surface so that it sublimes into a plume of gas, which will create a thrust.

‘We assessed all these methods; we wanted to maximise the deviation while minimising the mass of the spacecraft and the time from the launch to the potential impact with the Earth. If we have a very light spacecraft that can produce a large deviation in a short time, that’s a very good technique,’ Vasile said. Both the nuclear option and the mirror bees seemed favourable, but the risk of launching nuclear weapons into space makes this method impractical, he added.

A single mirror would be effective, but it would need to be up to 10km across, he said; but using technology from missions involving constellations of satellites, multiple spacecraft could be flown in formation, with smaller mirrors, to focus the sunlight onto a single spot, 1-1.5m across. ‘If we have a satellite with a mirror 2m in diameter, we would need 1000 of them, and they’d have to focus the sunlight for 90 days to deflect an asteroid the size of Apophis,’ he said. ‘But if we go up to 20m, we’d need ten satellites and 200 days.’ The satellites would weight about 500kg, which is lighter than the satellites for the Galileo global positioning system, he added. ‘It’s well within our launch capabilities.’