Space Tethers: Slinging Objects in Orbit?

What do you get when you combine a high school library, an intercontinental ballistic missile, and a machine that makes sexy underwear? The answer is scheduled to blast off into space tonight.

It's a woven string over half-a-mile long, called a "space tether." Some researchers believe that, in the future, cleverly positioned tethers could let people move things around in outer space without needing rockets.

This particular tether is the creation of Rob Hoyt, a physicist and aerospace engineer who lives in Washington state. The story behind it goes back to Hoyt's high-school days. One day, Hoyt was in the library, and he picked up a book called The Flight of the Dragonfly.

"I looked at the author blurb on the back," he remembers. "It said something like, 'Robert L. Forward spends half of his time writing science fiction and the other half of his time working on advanced space propulsion technologies for NASA.' And, you know, I read that and I thought, 'Boy that's the job I want to have.'"

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Hoyt went on to get a degree in physics, then went to graduate school. That's when he attended a lecture by that same science-fiction author; Robert Forward was talking about "space tethers."

For 50 years, people have relied on rockets to move things around in space. But rocket fuel is expensive and heavy. As Hoyt sat in the lecture hall, he heard how much easier it would be to just fling things around using orbiting tethers.

"It's sort of like using the techniques of Tarzan to move around in space," explains Hoyt. "You're basically grabbing onto a long, high-strength rope and using it to swing you from one place to another."

But there was one problem.

"At the end of his talk, [Forward] said, 'Well, but none of this will really work right now,'" recalls Hoyt. "Because space tethers will get cut by orbital debris."

In other words, space junk would whack the tether and slice it in two. There are just so many billions of flecks of paint and dust and tiny micro-meteorites zinging around in orbit at incredible velocities, says Hoyt. It's a bad place to put a long thin cable that you hope will last for a long time.

The lecture got Hoyt thinking. Instead of studying for his graduate exams, he began designing a new kind of space tether. It's made of more than one strand, like a woven net, or a cat's cradle. If one strand gets cut, the others stay intact.

Hoyt wrote a letter to Forward. And eventually they started a company, Tethers Unlimited, which has gotten funding from NASA. The company makes tethers by starting with light but strong fibers, like Kevlar. Then the strands are woven together using a computerized machine.

"[That machine is] normally used for fabricating things like lacy edgings on Victoria's Secret undergarments," says Hoyt. "We've developed ways to use that to braid the multi-line tether structure that we're testing in space."

Soon, three tiny satellites will blast off from Kazakhstan on a modified Russian missile. Once in space, the satellites will deploy the tether. It's half a mile long and looks like a thin net made of gold dental floss. The tether will be anchored by a satellite at each end. Hoyt says the third satellite will crawl up and down the tether, taking pictures.

"We'll then inspect them, to see, over a course over several months, how many cuts the tether experiences," he says.

Engineers have tested other tethers in space. But this will be first experiment in nearly a decade.

"I'm excited about it," says Les Johnson, an expert on new propulsion technologies at NASA's Marshall Space Flight Center. "The data that they'll collect from this, if it's successful, is going to be very useful as we look at the next generation of tether systems."

Johnson thinks tethers have real potential. But he says it will be a while before they are used to move satellites or other things, because they are such a radically different approach to space transportation.

"Not that we're afraid of things new," Johnson says. "It's just before you've put them on a system, they've got to be demonstrated and proven and you've got to have a lot of confidence in them. We're still in the stages where we're proving this out."

If all goes well with the first experiment, Tethers Unlimited would like to send up another satellite. This one would spin around like a slingshot. Its tether would be nine miles long, and it could toss a small object toward the moon.

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