Can Transporters Be Far Behind?

Two NASA astronauts have suggested a new way to deflect an Earth-bound asteroid -- one that wouldn't involve landing a spacecraft on the celestial body, blowing it up with nuclear weapons, or in any other way subjecting it to Bruce Willis.

Instead, the crew of the so-called "gravity tractor" would use the spacecraft's thrusters to hover above the asteroid, and utilize the gravitational attraction between the craft and the asteroid to gradually pull it off course.

"You would use this small gravity force between the [spacecraft and the asteroid] as your towline to basically pull this thing," said NASA astronaut Edward Lu, who along with colleague Stanley Love devised the gravity tractor idea.

"If an asteroid is found to be at an impact trajectory with Earth … you will have many decades of notice," said Lu to National Geographic. "And it turns out that you only need to change its velocity by a very small amount in order to prevent a collision."

Indeed, the two astronauts maintain that, given about 20 years notice, NASA could launch a gravity tractor spacecraft capable of deflecting an asteroid 650 feet in diameter -- simply by towing it into a new trajectory, a process expected to take about one year.

While lacking a certain excitement -- more along the lines of the elegant space station docking scene in "2001," versus an "Armaggedon"-style explosion -- the gravity tractor would likely be a safer method than attempting to land on a tumbling asteroid, blowing it up, or attaching a booster rocket pack to it -- alternate methods suggested in the past by scientists and screenwriters alike.

"Landing means dealing with a rough surface with poorly known physical properties and somehow compensating for the asteroid's rotation, which wants to whirl your thrust[ers] … around like a lawn sprinkler," Love said. "Using gravity as a towline frees you from those messy details."

Besides, blowing up an asteroid -- or slamming a large spacecraft into one to break it into smaller pieces -- are just "bad ideas," added Lu. "If you do that, you better have a darn good idea where all those pieces are going." 

Granted, the probability of a large asteroid slamming into our planet is slim -- which makes now the perfect time to make plans for such an event, said Love.

"In my office, we do not wait until the building is on fire to conduct fire drills," the astronaut said. "Recent large natural disasters, such as the tsunami in the Indian Ocean and the hurricanes in our own country, underscore the value of being prepared for an emergency."

While it's nothing to lose sleep over, we may soon have the chance to test the gravity tractor concept.

99942 Apophis, a 1,000-foot asteroid scheduled to come within about 19,000 miles of Earth in 2029, will have its orbit altered by the event to the point it might -- might -- hit our planet when it comes back around in 2036. (The odds are about 1 in 5,000.)

"If around 2013 we find out that it's going to hit, we could [initiate] a very tiny change in [the asteroid's] orbit before 2029," Lu said.

FMI: www.nasa.gov