Asteroid Threats Could Be Steered Away

Feb. 20, 2007 —It lacks the fanfare of a Hollywood drama, but using gravity to gently steer a threatening asteroid is a far better option than blasting it to smithereens, says a group of astronauts and scientists.

The Association of Space Explorers is lobbying the United Nations to take charge of deciding if, when and how to protect the planet from an approaching asteroid.

It's not a hypothetical exercise.

NASA has been tasked by Congress to identify 90 percent of near-Earth asteroids large enough to cause global devastation. The agency recently was directed to hone its search for rocks as small as 459 feet (140 meters) in diameter, which could cause significant damage on a regional scale.

So far, NASA has about 5,000 asteroids in its database.

"In the future, we're going to have 100 times more. We'll have a half-million in 20 years," Apollo astronaut Rusty Schweickart said at the American Association for the Advancement of Science meeting in San Francisco.

An asteroid known as Apophis already has caught NASA's eye. Experts estimate there is a one in 45,000 chance the space rock will smash into Earth in 2036.

Granted, those odds aren't high, but there is currently no plan or proven technology to take action if the risk of a strike grows as Apophis' orbit becomes better known.

For that reason the time to take action is now, said Schweickart, who is spearheading the effort by the Association of Space Explorers to bring the issue before the United Nations.

The group, a professional organization of astronauts, cosmonauts and others who have orbited Earth, has organized a series to workshops to develop a blueprint for the United Nations to consider. Schweickart hopes to bring a formal recommendation to the U.N. Committee for Peaceful Uses of Outer Space by 2009.

Scientists estimate Apophis, which is about 1,000 feet (320 meters) in diameter, would not cause global damage, but it certainly has the power to decimate a major city or even a state the size of California. Apophis' projected path spans a good portion of the globe, from Siberia to the west coast of Africa.

"It's not just Apophis we're looking at," Schweickart said. "We need a set of general principles to deal with this issue."

The favored approach to dealing with a potentially deadly space rock is to dispatch a spacecraft that would use gravity to alter the asteroid's course, said astronaut Ed Lu, a veteran of a long-duration mission aboard the International Space Station.

The so-called Gravity Tractor could maintain a position near the threatening asteroid, exerting a gentle tug that over time would deflect the asteroid's path enough to miss Earth.

An asteroid the size of Apophis would take about 12 days of gravity-tugging, Lu said.

Mission costs are estimated at $300 million.

Setting off explosives to move the asteroid would litter space with debris, which might become threats to Earth as well, Lu added.

The astronauts would like to see NASA stage a demonstration mission to test the concept before it would actually be needed to change an asteroid's orbit.

"You don't want to be in the position where the very first time you try something it's the real thing," Lu said.