"Killer Asteroid" Debate Pits Gravity Tractors Against Bombs, Projectiles

Victoria Jaggard
National Geographic News
March 8, 2007

An unusual type of arms race involving nuclear bombs and supermassive spacecraft has been heating up this week in Washington, D.C.

Each team of players hopes to be the one to design the U.S. government's weapon of choice for deflecting so-called near-Earth objects (NEOs)—comets and asteroids that could be on a collision course with Earth.

The debate has been raging among experts about which solution will be the safest, cheapest, and most reliable.

Ed Lu, a NASA astronaut and physicist, has been developing one of the leading contenders: a "gravitational tractor."

The proposed craft—weighing up to 20 tons (18 metric tons)—could nudge a 656-foot-diameter (200-meter-diameter) asteroid into a new orbit by the sheer force of the ship's gravity.

(Read "'Gravity Tractor,' Super Telescopes Enlisted to Battle Killer Asteroids" [February 17, 2007].)

"We have a controllable method right now" to deflect many potential NEOs, Lu said of the gravity tractor this week during the 2007 Planetary Defense Conference in Washington.

But "it's not ready yet," Lu told National Geographic News. "The technology is familiar, but it's not a case where we have one on the shelf we could send out tomorrow."

Nukes in Space?

Other experts argue that gravity tractors and other "slow push" methods are only viable when scientists have decades of warning before a potential impact.

Jesse Koenig of SpaceDev, Inc., made a case at the conference that the more timely solution is to use kinetic impactors.

Impactors are spacecraft intentionally crashed into an asteroid at high speed. The plan, Koenig said, is a simple, cheap way to solve the problem with only a few years' notice.

Continued on Next Page >>


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