starship-design: Plasma rocket engine makes space flight much faster - 10 Feb 2000

["L. Parker" <lparker@cacaphony.net>]

Step on it

Plasma rocket engine makes space flight much faster

Artist’s 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 m
icrogravity, 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)



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