Tethered Transportation In Space

March 26, 1999

NASA plans to lasso energy from Earth's atmosphere with a tether as part of the first demonstration of a propellant-free space propulsion system, potentially leading to a revolutionary space transportation system.

Scientists and engineers at NASA's Marshall Space Flight Center in Huntsville, Ala., are experimenting with tethers as part of a continuing effort to dramatically reduce the cost of space transportation.

Flight demonstration of the Propulsive Small Expendable Deployer System -- called ProSEDS -- is scheduled for August 2000. ProSEDS is one of the Future-X flight experiments selected recently by NASA to help mold the future of space transportation.

The experiment will demonstrate the use of an electrodynamic tether -- basically a long, thin wire -- for propulsion. An electrodynamic tether uses the same principles as electric motors in toys, appliances and computer disk drives, and generators in automobiles and power plants. When a wire moves through a magnetic field, an electrical current results. The unique type of electrical circuit created by the flow of electricity through the wire results in a magnetic field that drags or pushes on an external magnetic field.

An electrodynamic tether works as a thruster because a magnetic field exerts a force on a current-carrying wire. When electrical current flows through a tether connected to a spacecraft, the force exerted on the tether by the magnetic field raises or lowers the orbit of the satellite, depending on the direction the current is flowing.

"The working principle of electrodynamic tethers is not new, but the application to space transportation will be revolutionary," said Les Johnson, principal investigator of the ProSEDS experiment. "Imagine driving your car and never having to stop for gas -- that's what a tether does for a spacecraft in Earth orbit. Tether propulsion requires no fuel, is completely reusable and environmentally clean, and provides all these features at low cost."

While tethers have been successfully tested in space, ProSEDS will use a radically different and more efficient scheme for collecting current. Most of the metallic tether will be exposed to the environment of space, instead of covered with an insulating sleeve as in previous electrodynamic tether missions. The bare tether, about as thin as dental floss, will collect electrons directly.

Electrodynamic tethers used for propulsion in low-Earth orbit and beyond could significantly reduce the weight of upper stages used to boost spacecraft to higher orbit. Much of the weight of any launch vehicle is the propellant and it's expensive to lift heavy propellants off the ground. Since electrodynamic tethers require no propellant, they could substantially reduce the weight of the spacecraft and provide a cost-effective method of reboosting spacecraft, and potentially, the International Space Station.

Launched on a Delta II rocket from Cape Canaveral Air Station, the ProSEDS experiment will demonstrate the use of tethers for generating significant thrust in space by decreasing the orbital altitude of the Delta II second stage. The Small Expendable Deployer System will deploy a 3.1-mile, bare-wire tether connected with a 6.2-mile nonconducting tether from the Delta II second stage to lower its orbit.

The primary objective of demonstrating thrust with the tether should be achieved during the first 24 hours of the experiment. Performance measurements will be collected and transmitted continuously to the ground from the time of deployment until the experiment concludes a few days later.

"More than 40 percent of launches projected over the next 10 years have payloads with intended destinations beyond low-Earth orbit," noted Leslie Curtis, manager of Marshall's Space Transfer Technologies project. "Low-cost upper stages and on board propulsion systems are absolutely critical elements in reducing space transportation costs."

The ProSEDS experiment is managed by Marshall's Advanced Space Transportation Program, which is paving the highway to space by developing innovative technologies to dramatically reduce the cost of space transportation. NASA's industry team for the ProSEDS experiment includes: Tether Applications of Chula Vista, Calif.; Tethers Unlimited of Seattle; Electric Propulsion Laboratory of Monument, Colo.; The Michigan Technic Corp. of Holland, Mich.; Triton Systems Inc. of Chelmsford, Mass.; Smithsonian Astrophysical Observatory of Cambridge, Mass.; Alpha Technologies of Huntsville; Colorado State University in Fort Collins; and the University of Michigan in Ann Arbor.
Note to Editors/News Directors: Interviews, photos and video supporting this release are available to media representatives by contacting June Malone of the Marshall Media Relations Office at 256-544-0034. For an electronic version of this release, digital images or more information, visit Marshall's News Center on the Web: http://www.msfc.nasa.gov/news For more information on the Advanced Space Transportation Program, visit its Web site: http://astp.msfc.nasa.gov For more information about space tethers and their potential applications, visit: http://infinity.msfc.nasa.gov/Public/ps01/ps02/space.html

NASA/Marshall Space Flight Center News Center

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