A swarm of pebble-sized spacecraft could deflect an asteroid on a collision course with Earth, if launched early enough, British researchers say.

Aerospace engineers Alison Gibbings and Massimiliano Vasile at the University of Strathclyde say they've calculated a 1,000-pound swarm of pebble-sized spacecraft would deflect a fast-moving, 800-foot asteroid by nearly 22,000 miles, enough to avoid a collision, NewScientist.com reported.

However, the swarm would have to be launched in time to meet the asteroid eight years, or about three orbits, before the predicted Earth impact, the researchers said.

Such a swarm could be launched from Earth in a single rocket and then released as a tight cloud directed at the asteroid, they said.

One advantage is that the pebbles would be too small to crack the asteroid into possible dangerous pieces, they said.

Gibbings and Vasile reported on their proposal at the Astrobiology Science Conference in Atlanta last month.