Trimming travel time between Earth and various space targets is crucial to keeping human and robotic surveys of the solar system prospering into the 21^st Century.

Faster rockets cut back on an astronaut's radiation intake. Being a space speedster may also reduce loss of bone and muscle mass, as well as limit circulatory changes due to prolonged microgravity exposure.

One approach to express lane rocketry is tagged the Variable Specific Impulse Magnetoplasma Rocket (VASIMR). With VASIMR's oomph, a 10-month one-way trek to Mars -- the standard assumed for today's chemical rockets -- would be reduced to just four months.

Research on this high-tech propulsion method has turned controversial, however. VASIMR supporters see dream machinery in the making. Other propulsion experts claim the engine delivers more hype than hypervelocity.

Work on VASIMR is ongoing at the Advanced Space Propulsion Laboratory at NASA's Johnson Space Center (JSC). The laboratory was anchored at JSC in December 1993.

The lab director is NASA astronaut Franklin Chang-Diaz, a long-time plasma rocket believer who has been hard at work on the idea since 1979. He holds a doctorate in applied plasma physics and fusion technology from the Massachusetts Institute of Technology (MIT).

Despite shoestring budgets, VASIMR is a stay-the-course labor of love for Chang-Diaz and his colleagues.

"I don't want to change anything right now," Chang-Diaz told SPACE.com. "We have an outstanding team that is growing by the minute. The results that are coming out of the experiment at this moment are awesome. Everybody is excited about what we're doing."

The concept first jelled at Charles Stark Draper Laboratory in Cambridge, Massachusetts, then was picked up at the MIT Plasma Fusion Center before moving to JSC.

A VASIMR rocket system consists of three major magnetic cells denoted as "forward," "central" and "aft." To get the rocket roaring, a neutral gas, typically hydrogen, is first injected at the forward-end cell of the motor and ionized. This electrically charged gas is then heated to create a desired density in the engine's central cell.

The heating is done by the action of electromagnetic waves, similar to what happens in a microwave oven.

After heating, the plasma -- essentially a superheated gas -- enters a two-stage hybrid nozzle at the aft-end cell. Here the plasma detaches from the magnetic field and is exhausted to provide "modulated" thrust. This VASIMR configuration guides and controls the plasma over a wide range of temperatures and densities.

The real plus for this propulsion technology is being able to vary or modulate the plasma exhaust while maintaining maximum power. This technique works like the function of the transmission in a conventional automobile. That is, you have engine power either for speed when driving on a level highway or for torque over hilly terrain.

Two parameters are varied during a typical engine operation: thrust and the velocity of the particles being exhausted. This latter factor is called the specific impulse. As a VASIMR ship accelerates on its journey, the thrust decreases and the specific impulse increases. The opposite is true as the ship slows down at its destination.

The end product from VASIMR is a plasma exhaust. Plasma is often called the fourth state of matter and is common to the Sun's atmosphere, among other places.

Chang-Diaz terms VASIMR "a power-rich, fast-propulsion architecture" that could lead to fusion rockets.

The VASIMR wonder rocket is chock-full of technology. Its high-tech innards involve superconducting magnets working at space temperatures; tightly packaged power generation and conditioning gear; compact and robust radio frequency systems; a hybrid magnetic nozzle; and lightweight heat shields and cooling technology.

Along with Johnson Space Center experts, VASIMR's talent pool draws from seven universities and two national laboratories, such as MIT, Oak Ridge National Laboratory, Rice University and the University of Texas at Austin.

"It's an expanding research effort," Chang-Diaz said. "We're developing something that is very new and very different from the established electric propulsion framework."

One VASIMR study hypothesized using a 200-megawatt nuclear power system. The result, he added, showed that 20 metric tons could be delivered to Mars in 39 days.

"Now that's the way you want to go," Chang-Diaz said. "Astronauts will really warm up to that idea very quickly. So if you're going to go nuclear, go all the way. Go with the gusto."

Ballistic bravado aside, VASIMR faces a funding challenge to stay alive.

In 22 years of working on the project, finding money has always been an ongoing wrangle, Chang-Diaz admitted. "But it seems to be more of a struggle now for some reason. Our funding right now is our major limitation. That has become pretty clear."

To run the JSC Advanced Propulsion Laboratory takes on the order of $1.4 million a year. That budget includes an entire team of some 50 scientists from all over the United States, Chang-Diaz said.

Loads of small visionary projects vie for small pots of NASA's advanced propulsion money. There are lots of mouths to feed, the astronaut said, keeping everybody on a starvation diet. Not a very conducive scenario for people to work together, he said, and that tends to polarize propulsion groups.

VASIMR seems to be as polarized as any technology at JSC. Mention the project to certain propulsion specialists and you get instant lip-biting.

It's clear there are two camps of thought about VASIMR. The classical electric propulsion community, responsible for engines like the ion thruster used in Deep Space 1, generally feels there are fundamental flaws that will prevent the VASIMR engine from performing as purported. Then there's the cadre of high-energy plasma experts that disagree with them.

For instance, one space propulsion expert critical of VASIMR observed that for the thruster to be useful for a human mission to Mars it needs four to six megawatts of power. This amount of power can only come from a very large on-board nuclear reactor. That hardware does not exist, and probably will not exist for quite some time, the expert told SPACE.com.

Chang-Diaz said he's heard the caustic comments before. "There's a whole group of people who see it completely different than the critics. We have people in the nuclear engineering community that are very supportive of our effort," he said.

"One of the greatest criticisms that we had over the years was that the VASIMR magnets were too heavy," Chang-Diaz noted. "We now have magnets that are 30 times lighter, and they are fully superconducting. We just started testing our first high-temperature, superconducting magnet. People are beginning to see that the technology does make sense."

That said, VASIMR is still a work in progress, the astronaut explained. "There's a lot of physics that is not yet known," he said. "Even the people in the fusion community are coming to our aid to help us decipher the problems. I'm happy to see that happening now."