Moon Miners' Manifesto

#104 April 1997

NRO Studying Tethers to Connect and Power Satellites

[http://hyperspace.nrl.navy.mil/TIPS/ - 3/17/97]

CAPE CANAVERAL, Fla. (AP) - For nearly a year, America's "other space agency", the super-secretive National Reconnaissance Office, has been monitoring a bright, white object streaking through the night sky. It's not a UFO. It's 2 1/2 miles of knitting yarn. The single strand of reinforced acrylic yarn has been orbiting Earth, unwound, since last June.

The NRO is intrigued by the possibility of using tethers to connect clusters of small satellites so they can communicate like a computer network.

Other tantalizing applications: using tethers to power spacecraft by generating electricity as the conductive cords sweep through Earth's magnetic field, to propel spacecraft into different orbits and to drop experiments from a space station.

This is the longest-lasting space tether yet, a $4 million experiment to demonstrate the motion and survivability of tethers in low Earth orbit, littered with micrometeoroids as well as space junk. It's also the first unclassified, ongoing space project in the 36-year history of the National Reconnaissance Office. The NRO typically flies spy satellites.

The NRO has some things to be closemouthed about. The NRO refuses to say how or when the shoe-string-like tether was rocketed into orbit or how or when its next tether experiment will fly. Until December, all NRO launches were classified for so-called national security reasons.

On the record: The Tether Physics and Survivability experiment, called TIPS, was ejected from a classified military satellite on June 20, 1996, into a 635-mi. high orbit that swings as far north as Alaska and as far south as Chile's Cape Horn. A few hours later, the yarn - all 2 1/2 miles - was unreeled from a spool. The tether, weighing 12 lbs, was bowed and swung like a jump rope, but eventually straightened and became more perpendicular to Earth.

Nine months later, the yarn still is orbiting Earth, intact, monitored by ground-based laser, radar and telescope observations. Amateur astronomers also keep unofficial tabs on the tether. (It's visible with binoculars on a clear night, although you need to know exactly where and when to look.)

TIPS has outlived its predecessors by months. NRO officials say if the tether isn't broken by a micrometeoroid or other debris, it could orbit for as long as 27 years before plunging through the atmosphere and burning up.

When a tether last flew, aboard Columbia in Feb.y 1996, its 12-mile conductive cord snapped within five hours because of an electric discharge. The satellite drifted away like a lost balloon. On the first flight of the $400 M NASA-Italian Space Agency system, aboard Atlantis in '92, a protruding bolt caused the tether to jam a mere 840 feet out.

Despite the trouble, the two missions proved electricity could be generated by a tether system - easy power for spacecraft. The unintended severing of the tether demonstrated that the higher of two objects goes up when a tether is cut and the lower one goes down slightly - a fuel-free way to boost spacecraft into longer-lasting orbits. A shuttle could depart from the future space station via a tether. Once that tether is cut, the shuttle would drop and the station would rise - a win-win situation.

NASA successfully flew three simpler and cheaper tethers on unmanned Delta rockets in the early 1990s. The third test ended abruptly, however, when its 12-mile line was severed, most likely by a micrometeoroid, three days after it was unreeled.

NASA's next shot at a tether? Not until 1999 and most definitely not on a space shuttle, where astronaut safety is paramount. A tether experiment to have flown on Discovery this July, was dumped.

"Things have really been ramped back because of the squeeze on the budget and the bad experience we've had with tethers," said NASA project manager Jim Harrison. Added astronaut Jeffrey Hoffman, who flew on both tethered-satellite missions: "It's an emotional impact. What can you say? It would have been better if it hadn't broken."

Unlike NASA, the NRO wanted as plain a tether system as possible.The 2 1/2 miles of white yarn is wrapped in braided Spectra 1000, a tough, white fiber used in bulletproof vests and fish lines. The nonconductive cord is a tenth of an inch thick.

On either end of the TIPS tether is an aluminum, hexagonal box covered with 18 laser reflectors. The box containing the NASA-donated unreeling device and long-dead electronics has a mass of 83 pounds. The other box is 23 pounds.

The NRO and NRL aren't the only ones picking up where NASA left off. The engineer who developed the TIPS tether, Joe Carroll of Tether Applications in Chula Vista, Calif., has a 22-mile cord supposed to ride on a European Ariane 5 rocket later this year. He's also working on a tethered capsule that might be used to return experiments from the future international space station. Rob Hoyt of Tethers Unlimited in Seattle is working on a fishnet stocking-type tether. If one string breaks, the tether still holds.

Hoyt's most far-flung project: rotating tethers that hurl payloads from Earth orbit to the Moon. As for the space elevator envisioned by science fiction writer Arthur C. Clarke, lifting people and cargo to geosynch orbit 22,300 miles up, that's farfetched - for now. No material currently exists that's strong enough, yet affordable, for such a long, long tether. "You get on an elevator and you push a button to go to geo," Carroll said. "That's the 10-millionth floor. That's going to take a while."

NRO

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