High risk, high payoff
MXER tethers are considered by NASA to be "high risk with high payoff," said Les Johnson, Manager, In-Space Propulsion Technology Projects at the NASA Marshall Space Flight Center in Huntsville, Alabama.
Efforts at this time are geared to examining the technologies that will make or break MXER for use as an in-space transportation system, Johnson told SPACE.com.
Johnson said that MXER contract awards are focused on rendezvous and capture techniques, stability of the tether, as well as strength and survivability of the cable as it speeds through space.
"We are years away from a system-level space demonstration, though not as far as many might naively think. If these key issues can be worked, as we believe they can, MXER tethers might be a viable candidate for use in space by the middle of the next decade," Johnson said.
Sketchy past
Hoyt said that the beauty of the MXER tether is in its reusability. Once the first system is up, fully functional and swinging away, that early hardware can be used to recoup the initial investment on developing the technology.
No doubt, given a somewhat sketchy past, a MXER tether needs a solid shakeout in space.
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| The Momentum-Exchange/Electrodynamic-Reboost (MXER) Tether System could pick payloads up from a reusable launch vehicle in low Earth orbit and toss them to geosynchronous orbit. This idea could act as a Hypersonic Airplane Space Tether Orbital Launch system, or be utilized to handle other launch systems other than hypersonic airplanes. CREDIT: Tethers Unlimited, Inc.
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| Tether System rotates like a giant sling, swinging down and picking up spacecraft launched into low orbits and then tossing them to higher orbits or even tossing them to other planets. CREDIT: Tethers Unlimited, Inc.
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| Artist's concept of the low-cost µTORQUE idea, short for Microsatellite Tethered Orbit-Raising Qualification Experiment. Concept involves spin-up of a tether deployed from a rocket upper stage, with tether then tossing a microsatellite to the Moon. CREDIT: Tethers Unlimited, Inc.
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|  | TODAY'S DISCUSSION | | |
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NASA has had a couple of high-profile setbacks with tether experiments over the years. But Hoyt counters that at least 17 tether trials have been conducted on-orbit so far. The majority of them have been highly successful, he said.
"Even the ones that didn't go perfectly taught us a great deal. The failures that did happen were more the result of human error and our imperfect understanding of complex technologies rather than any fundamental problem with the technology," Hoyt said. Furthermore, look at how many rockets the early astronauts watched blow up before they rode them into the sky, he added.
Building trust
To help build space community trust in tethers, Hoyt said that several low-cost flight experiments could be flown by late 2004 or early 2005.
The first such confidence-builder is the "Multi-Application Survivable Tether", or MAST experiment.
This NASA-funded work couples Tethers Unlimited with students and faculty at Stanford University. The project entails deployment of three tiny spacecraft along a lengthy tether. The MAST experiment would show off numerous key technologies, such as tether designs that can survive in space and momentum-exchange propulsion.
"We hope to build upon that experience to fly a very cool mission a couple of years later that will demonstrate electrodynamic tether orbit-raising, and then graduate to a full MXER tether flight demonstration at the end of the decade," Hoyt said.
Space tethers have such a huge potential payoff for lowering the cost of space missions, Hoyt believes. "It's inevitable that people will keep trying them until they get it right."
advertisement%20Tether%20System%20could%20pick%20payloads%20up%20from%20a%20reusable%20launch%20vehicle%20in%20low%20Earth%20orbit%20and%20toss%20them%20to%20geosynchronous%20orbit.%20This%20idea%20could%20act%20as%20a%20Hypersonic%20Airplane%20Space%20Tether%20Orbital%20Launch%20system,%20or%20be%20utilized%20to%20handle%20other%20launch%20systems%20other%20than%20hypersonic%20airplanes.%20CREDIT:%20Tethers%20Unlimited,%20Inc.)
