8 May 2010
News - Vehicles (Good)
Taking Out the Space Trash
Using laser tractor beams to clear LEO
by Carol Pinchefsky
Here on Earth, the problem of trash has become an eco-minded opportunity for recycling and reuse. But in space, trash is nothing but a problem. Debris in low Earth orbit ( LEO), such as rocket slag and defunct satellites, are becoming a congestion hazard.

But help is on the way. New Scientist reports that a far-thinking (and possibly eco-minded) scientist at Nagoya University, John Sinko, has designed a 'tractor beam' to not just push space junk out of potential harm's way but also potentially control spacecraft and satellites too.

"Sinko's idea is based on an experimental type of spacecraft engine called a laser thruster. Inside these motors, laser pulses fired into a mass of solid propellant cause a jet of material to be released, pushing the craft in the opposite direction," wrote Paul Marks.

Of course, the idea of using lasers to both track the position of space debris and also to take out the trash is not new -- both NASA and the US Air Force have investigated the idea, sometimes called a "laser broom". (See for example, the 1997 paper "Orion's Laser: Hunting Space Debris".) Hit anything with enough intensity of light on one side, and you'll cause a little bit of it to vaporize. In space, that translates into a slight push, altering the orbit of the target to either cause it to fall back into the atmosphere and burn up, or into a more distant so-called graveyard orbit, safely out of the way of satellites and spacecraft.

Unfortunately, the graveyard orbit is still not far away enough to prevent problems, such as micrometeorites that tear into space junk, releasing particles that make their way down to the orbit of operational equipment. This can cause a chain reaction...of bad (also known as Kessler syndrome).

Sinko is taking the idea a step further, however, looking to use lasers not only to steer junk but also for precise control of spacecraft, with the lasers not necessarily even on the craft itself, but positioned elsewhere in orbit.

The idea is valuable because traditional propellant is in very limited supply on most spacecraft and satellites, and once it's gone, it's gone. The idea works for debris because all of its mass is expendable. A spacecraft "motor" by contrast could be made from specialized ablative materials that expel matter either forward or backward depending on the wavelength of the incoming light beam, allowing a remote laser to "pull" as well as "push," hence "tractor beam." The ablative material can still run out -- it's still propellant, of a kind -- but the "laser engine" can do more with less, especially if the laser isn't even on the craft at all.

So, it looks like space might be full of spacecraft and satellites all targeting each other with lasers, just like we've been anticipating ever since Star Wars. And with all of this pushing and pulling with lasers, it seems as if the force will be with us.
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Carol Pinchefsky 8 May 2010
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