Plasma rocket engine

Step on it

Plasma rocket engine makes space flight much faster

Artistís concept of the plasma rocket. The prototype is being developed by the Fusion Energy Division at the Oak Ridge Centers for Manufacturing Technology.

It may not be warp speed, but a new rocket engine concept in design at the Oak Ridge Centers for Manufacturing Technology could make space flight a much faster business than it is already. That would be good news for astronauts facing long stretches away from home on interplanetary missions.

ORCMT’s Radio Frequency (rf) and Microwave Technology Center at the Oak Ridge Centers for Manufacturing Technology is collaborating with NASA to develop a high-powered plasma rocket engine prototype, a concept NASA will consider for high-speed interplanetary propulsion. The system is being designed as proof-of-principle for the Variable Specific Impulse Magnetoplasma Rocket, or VASIMR.

According to Stan Milora of ORNL’s Fusion Energy Division, where the ORCMT center is located, a gas with a low molecular weight, probably helium, will be ionized, heated with rf waves and expelled from the rocket engine.

“You can provide thrust in two ways: with low velocity and high mass flow like a liquid-fueled rocket, which is very inefficient, or with a plasma, which expels the propellant at millions of degrees versus thousands,” Milora says. “This would be a rocket with much increased fuel economy—you could taker longer trips with higher payloads because less weight would be devoted to fuel.”

The VASIMR’s plasma, which consists of helium ions and electrons, is generated by a helicon plasma injector and confined and shaped by high-temperature superconducting magnets. The plasma would be guided through a rocket chamber formed by a magnetic field and further heated by rf waves at ion cyclotron frequencies.

“The helium can be heated to very high temperatures, which provides a directed, very high-velocity exhaust plume,” Milora says. “The magnetic field is like a hose. As the helium ions come down the hose, spinning at the cyclotron frequency, we jack ’em up further with the rf power tuned to that frequency.”

What comes out of the rocket’s magnetic nozzle is 1 million degrees hot, at a velocity of 70,000 meters per second.

The plasma rocket would use propellant in relatively small amounts compared with a conventional chemical rocket for the same mission. In a real mission, conventional rocket engines would be used for lift-off from Earth. Once in space, the craft would switch to the plasma engine and accelerate continuously instead of coasting to its destination after a short-duration, high-thrust “burn.”

The first flight of the VASIMR could come as early as 2001. NASA is considering testing the technology on a dual-purpose mission called the Radiation and Technology Demonstration mission. In addition to its main technology demonstration objectives, the spacecraft will carry radiation-measuring instruments and will undertake a comprehensive survey of the Van Allen radiation belts.

The VASIMR engine is being developed in a partnership with NASA’s Advanced Space Propulsion Laboratory as well as private industry and a number of U.S. universities. ORCMT has the main responsibility for VASIMR’s rf and superconducting magnet systems. ORNL’s Fusion Energy Division has been DOE’s lead rf laboratory for fusion energy applications for the past decade and is involved in R&D aimed at commercial applications of high-temperature superconductors.

A successful design would give NASA tremendous leeway in extended missions because so much less spacecraft payload would be devoted to fuel. VASIMR would provide for a wide range of mission abort capabilities, an essential element for human flight. The higher speeds from continuous acceleration would also be important to crews on manned missions.

ORNL health physicist and mathematician Troyce Jones maintains that long-duration space flights could have a very deleterious effect on crews subjected to loss of bone mass (and associated immune system effects) from microgravity, high radiation and even months of crummy food. Milora acknowledges that the prospects of faster speeds have been appealing to the NASA collaborators.

“We’re working with an astronaut on this,” Milora says. “Getting there fast is certainly a driver.”—B.C. (reported by Bill Wilburn)