An asteroid cop gets ready to patrol

A satellite the size of a suitcase may soon protect our planet from a catastrophic collision with an asteroid. Dubbed NEOSSat – for Near Earth Object Surveillance Satellite – the Canadian craft will be the world’s first space telescope designed to hunt asteroids that threaten to slam into Earth.

Several ground-based telescopes already scan the sky for potential dangers, but they only hunt at night and poor weather obscures their view. By circling pole to pole in a sun-synchronous orbit about 500 miles above Earth, NEOSSat can operate nonstop, twirling hundreds of times a day as it photographs sections of space, says Alan Hildebrand, a planetary scientist at the University of Calgary in Alberta.

NEOSSat’s six-inch wide telescope has a sunshade that lets it search close to the sun, where potentially hazardous asteroids are concentrated.

“We’ll be regularly searching the part of the sky that telescopes on the ground are unable to search, so it makes us a little bit safer,” says Mr. Hildebrand.

Hildebrand points out that while collisions are rare, we need only look at the surface of the Earth, the moon, and Mars to see craters left behind by past impacts. He estimates that large asteroids (bigger than 1,000 yards wide) smash into Earth once in a million years. Many scientists believe such a crash 65 million years ago created the 150-mile wide Chicxulub crater off the coast of Mexico and led to the severe climate change that wiped out the dinosaurs.

Asteroids don’t have to be that big to cause disaster. Smaller asteroids strike Earth every few centuries. A hundred years ago this summer, a small asteroid burst just a few miles above the ground near the Tunguska River in a remote part of Siberia. Scientists believe that asteroid was roughly half the size of a football field, and the explosion devastated a 1,200-square-mile area.

“It would be one of the greatest disasters in human history were it to occur over a major city,” says Hildebrand. “The city would be flattened.”

The spacecraft, jointly funded by Defence Research and Development Canada and the Canadian Space Agency, belongs to a new class of microsatellites. Weighing just 150 pounds, NEOSSat also carries a small price tag – a mere $11.5 million in an industry where huge satellites can cost $500 million. Scheduled to launch in 2010, the craft will piggyback on a rocket as a secondary payload and will operate for at least one year.

If NEOSSat discovers an asteroid likely to hit Earth, there are a couple of options, says William Harvey, project manager with the Canadian Space Agency in Ottawa, Ontario. If given short notice, governments can only move people out of the way. If given more time, a space mission could be sent to deflect the asteroid.

Scientists have discovered more than 5,400 near-Earth asteroids since they started cataloging them about 20 years ago. (Near-Earth means within 120 million miles, a distance greater than from here to the sun.) Some 800 of those asteroids are larger than 1,000 yards wide. But Hildebrand calculates there are more than 200,000 smaller asteroids. “We’ve got a long ways to go,” says Hildebrand. “Suffice to say that in this game, we would like to find them all.”

When not asteroid spotting, the dual-use craft will track satellites and space debris to prevent collisions. More than 2,200 objects orbit the planet in mid- to deep-space, including 300 satellites. The rest are spent rockets, defunct satellites, and other bits left from previous missions. And space is getting crowded as more than 50 new satellites launch every year.

Various forces such as lunar pull and solar pressure can nudge these objects off orbit, says Brad Wallace, a scientist with Defence Research and Development Canada in Montreal. While rare, collisions create a high-velocity impact. In 1996, a fragment of a launch vehicle that exploded 10 years earlier smashed into a French satellite, causing it to spin out of control for a while until scientists could stabilize it. If NEOSat sees that a satellite is in danger, “the only countermeasure we can take is just to get [it] out of the way,” by reprogramming the spacecraft’s orbit, says Mr. Harvey.

While doomsday movies like “Armageddon” and “Deep Impact” make great Hollywood fare, this isn’t science fiction, says Harvey. “It’s a real event; it happens.” And NEOSSat’s job is to see the asteroids coming.