What's the News: The many bits of space junk orbiting Earth, from foil scraps to lens caps to chunks of frozen urine, can damage satellites and spacecraft, which is why researchers have long sought methods to remove debris from orbit. Scientists at the U.S. Naval Research Laboratory have proposed a new way of taking out the trash (in two senses): They want to pump 20 tons of tungsten dust into Earth's orbit; this dust would exert drag on the junk's orbit, slowing it down and gradually lowering it until Earth's atmosphere can burn it up. This bid to protect Earth's 900 active satellites is controversial because the dust could potentially harm solar panels on satellites and obstruct astronomical measurements, but it's a handy fix because it doesn't require ambitious new technology. How the Heck:
The scientists say that their "dust snow plow" was inspired by the natural drag exerted by the Earth's atmosphere starting at around 900 kilometers: The atmosphere gradually slows down the orbit of junk at this range, pulling debris out of orbit after a number of years.
The 20 tons of 30-micrometer-wide particles of tungsten, which is denser than lead, would exert drag on the junk as the dust grains pummel the junk's surface, decreasing the junk's orbit to the 900 km level in about a decade.
After that, Earth's atmosphere should burn up both the dust and the junk within the next quarter of a century.
What's the Context:
There's an estimated 19,000 pieces of trash over 10 cm wide orbiting Earth, and an order of magnitude more that's less than 10 cm wide. The smaller junk is the most dangerous for satellites because, unlike the larger pieces, they're not tracked or catalogued, which means that researchers don't know beforehand if a satellite and a small piece of junk are on a collision course.
Scientists say that the dust shouldn't harm satellites because their "thermal blankets, spacecraft structure, [and] sensor baffles," are made to withstand dust grains. Plus, they say that satellites could position themselves above the tungsten dust layer.
From lasers to explosives, researchers have proposed many ways of cleaning up our space-age mess.
By far the oddest bid to reel in junk has been proposed by Japan's space agency, which wants to team up with a fishing-net maker to rope in debris. Yes, really.
Not So Fast:
Unless future solar panels are stronger than current ones, the dust cloud could harm them by scratching their surfaces.
There's still uncertainties as to how a cloud of tungsten in Earth's atmosphere would behave: The dust could potentially coalesce into a thick band that could interfere with the electromagnetic frequencies that astronomers use.
Even if the dust method worked and we pumped our skies full dust right now, it would take a third of a century (10 years to bring junk to the 900 km level and 25 to burn it out of the atmosphere) to see the full effect.
Reference: Gurudas Ganguli, Christopher Crabtree, Leonid Rudakov, Scott Chappie. "A Concept For Elimination Of Small Orbital Debris." arXiv:1104.1401v1Image: Gurudas Ganguli et al.
