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(Cheryl Carlin)

Satellite Smashers

Space-faring nations: Clean up low Earth orbit or you're grounded.

Installing a tether on the ground before launch is one thing. Attaching a tether, or any kind of de-orbit package, to a crumbling, tumbling rocket stage in orbit is another—particularly if the target has nothing for the package to hold on to, because it wasn't designed to be touched ever again by human or robot after being put in space.

JAXA engineers are looking at several options for wrangling such uncooperative targets. In one scheme, the junk removal satellite would dampen any tumbling motion of a large object by shooting small projectiles at it—ice pellets work nicely—before moving in to attach a tether.

In 2003, Tethers Unlimited designed a system called GRASP (Grapple, Retrieve, And Secure Payload), which used a net made of Kevlar yarn to snare a small object and steady it enough for a tether to be attached. With funding from the Defense Advanced Research Projects Agency, the company got as far as testing a prototype during short stretches of weightlessness on a zero-G airplane flying parabolic arcs. It worked, says Hoyt, but DARPA hasn't come through with money for a follow-on test.

And that, as usual, is the rub. No public or private entity has volunteered to research, let alone build, an operational junk removal system.

One would expect satellite owners and insurers to take an interest, but relatively few satellites in polar orbits are privately owned, and assigning blame for orbiting debris collisions is still a fuzzy area of the law. Who was at fault, asks Johnson, when an old rocket fragment and the Cerise satellite ran into each other in 1996? Neither object had the ability to maneuver, and the fragment had been orbiting for years before Cerise was launched. "There are no rules of the road in space," he says. And because collisions have been extremely rare, insurance premiums haven't risen enough to press satellite owners into doing something about the debris problem.

And so the junk multiplies. The last year alone has seen the two worst space-junk-producing events in history. Last February, leftover propellants in a two-ton Russian Briz-M rocket stage caused it to explode, producing about 1,000 new pieces of orbital debris. Fragments from rocket stage explosions make up the majority of space junk, and most satellite-launching nations have now learned to vent leftover propellant from used rockets so they don't turn into orbiting bombs like the Briz.

But the worst case of orbital littering ever was deliberate. On January 11, 2007, as part of an anti-satellite test, China slammed some kind of impactor into its own Fengyun 1C weather satellite. By year's end, 2,500 pieces of debris were being tracked. Last summer one of those speeding fragments forced NASA to hastily move its $1.3 billion Terra Earth-viewing spacecraft out of the way. These kinds of evasive maneuvers are no longer uncommon for large spacecraft, including the International Space Station.

Expect to see satellites undertake more and more debris-dodging maneuvers. And hope that somebody finds a way to lower the cost of building and deploying space junk collectors—in case those satellites can't dodge quickly enough.

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