"Rockets tend to work much better the hotter the exhaust is and the plasma allows you to go to temperatures millions of degrees rather than thousands of degrees in a conventional rocket engine," he said.
Plasma, known as the fourth state of matter, is electrically charged gas made up of atoms stripped of electrons. Plasma typically occurs in environments of high pressure and temperature, such as stars.
Thrust from the plasma engine could boost a spacecraft for a longer time and with better efficiency than conventional engines.
The heart of VASIMR is three magnetic cells that ionize, amplify the heating and direct the flow of the plasma. The superconducting magnets work a bit like a microwave oven by stimulating the hydrogen molecules, thus heating them.
Controlling and directing material as hot as a star has been a major challenge for researchers.
No known solid can contain such superhot gas, so superconducting magnets generate a field that corrals the plasma. Development of such magnets has been the key to development of the engine.
"To harness the plasma at those temperatures, the only way is…to have a very strong magnetic field to hold it together," he said. "The only way to create those fields in a reasonable way in space is with superconductors."
Another key feature of the plasma engine is its ability to throttle, which allows it to increase or decrease in thrust when needed to enter or escape a planet’s gravity. This is analogous to a car using a lower gear to climb a hill, then shifting to higher gear on the open highway.
High-temperature superconductors being developed with the lab at JSC along with corporate and academic partners may have applications in terrestrial power plants, according to Chang-Diaz.
Long-distance power
Electrical power could be transmitted effectively over long distances with little or no loss of electricity due to having no resistance in power lines, thus reducing load on power plants' capacity.
For now, the magnets in the lab’s engine draw power from a local electrical utility, but early tests near Earth will use solar arrays. Deep-space tests will likely require nuclear power to provide the wattage needed to heat the plasma.
Chang-Diaz said he hopes to get the engine tested in a vacuum chamber soon and to get a working model in space.
We’ve got an ongoing effort to gradually improve the envelope of the device," he said. "We hope to develop one for flight in space about mid 2004 so we can demonstrate how it actually runs."
Chang-Diaz has been researching plasma engines since 1979 and said the steady march of research still excites him.
"It becomes a reality more and more. In the early days it was just an idea and concept and nothing but a paper study," he said. "We’ve got some hardware that’s worked the way we thought."
Fusion history
If the project turns out to have applications for terrestrial power, this will be payback of a sort. VASIMR draws upon decades of Department of Energy research into using magnetically contained nuclear fusion as a power source.
Fusion programs since the 1950s have sought to compress light elements into heavier elements and liberate large amounts of energy in the process. But a persistent obstacle to fusion energy has been the difficulty of containing hot, electrically charged plasma.
Ironically, it was this confinement problem that led Chang-Diaz and others to look at how leaking plasma could be used for spacecraft propulsion. Researchers realized that allowing plasma to leak out in one direction would create thrust on a spacecraft.
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