Fans of shoot-em-up sci fi everywhere will be thrilled with the latest proposal for freeing the International Space Station (ISS) from the need to repeatedly alter its trajectory to avoid crashing into space junk. Researchers from the Riken Computational Astrophysics Laboratory of Japan want to instead use a laser system to zap dangerous space debris on a collision course with the ISS.
"We may finally have a way to stop the headache of rapidly growing space debris that endangers space activities," chief scientist at Riken, Toshikazu Ebisuzaki says.
The Earth's orbit is cluttered with almost 3,000 tons of space junk. According to NASA researchers, this junk is made up of decoupling rings, derelict satellites, rocket boosters, and small bits of wreckage like paint chips or screws created from collisions between larger objects. Most of these items are small and have little mass, but they can still inflict serious and even catastrophic damage on spacecraft and satellites-and the ISS. This is because they're moving at more than 22,000 miles per hour relative to their targets.
As more spacecraft and satellites enter the atmosphere the problem of space junk is becoming more serious. And of course every impact creates even more debris, worsening the problem. For these reasons new methods for dealing with the problem are a priority. With adequate shielding, most satellites and spacecraft can survive impacts from very small pieces of debris-say those 1 centimeter in diameter or smaller. Very large pieces of junk are relatively easy to spot and avoid, but pieces in the 1 to 10 centimeter range are tough to spot, and therefore tough to dodge.
To date the official space junk protocol has been to keep a lookout and then get out of the way to avoid impact. The crew moves the station just enough to avoid the collision and waits for the debris to pass in a docked craft capable of returning them to Earth should something go wrong.
The new Riken proposal, however, focuses on the Extreme Universe Space Observatory (EUSO). Although it was not designed for the purpose of obliterating space junk, the system, created for monitoring ultraviolet emissions caused by cosmic rays, may solve this problem. Astrophysicist Toshikazu Ebisuzaki says that use of the EUSO, which will be used on Japan's 2017 ISS module, is a good strategy.
The laser system uses a Coherent Amplification Network (CAN) laser, now under development for use in atom smashers, to blast pieces of junk by vaporizing its surface. The CAN laser generates a single, powerful beam by combining many small lasers together. This in turn pushes the debris into the atmosphere with the plume of plasma created by the blast. The junk would then burn up in the atmosphere.
A 100,000-watt ultraviolet CAN laser, the full-scale version of this system, would have a range of about 60 miles. It would be able to fire about 10,000 pulses per second, each pulse of a one-tenth of one-billionth of a second duration. This set of capabilities should be adequate to secure the ISS. The system's laser would need lithium-ion batteries weighing about 17 pounds.
"The EUSO telescope, which was originally designed to detect cosmic rays, could also be put to use for this useful project," Ebisuzaki says.
If the proof-of-concept and full-scale prototypes work, the researchers propose that a satellite version of the system be produced solely for the purpose of blasting space junk. The satellite would then orbit over both poles of the Earth. They believe it could zap about 100,000 pieces of space junk annually, one piece of junk every five minutes.
Most space junk is at an altitude of about 500 miles. The satellite would start its orbit at about 620 miles and over time drift downward at about 6 miles per month until most troublesome junk was gone-in about 50 months' time.
"The biggest obstacle is funding," says Ebisuzaki. "There are some technical challenges, of course, but the main issue is getting funding for development and launch."
The researchers published their findings in the journal Acta Astronautica on March 13.
