Posted on 08/07/2002 4:08:31 PM PDT by Brett66
Superfast VASIMR Rocket in Funding Limbo
By Leonard David
Senior Space Writer
posted: 07:00 am ET
07 August 2002
Trimming travel time between Earth and various space targets is crucial to keeping human and robotic surveys of the solar system prospering into the 21st 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.
The project was nearly scrapped several weeks ago, much to the chagrin of a NASA astronaut in charge of the effort. For now, VASIMR has received a stay of execution.
VASIMR 101
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.
Fourth state of matter
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.
Go with gusto
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."
Staying alive
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.
Critics corner
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."
In-space testing
One way to make good on the promise of VASIMR is through in-space testing.
This week, Chang-Diaz heads for NASA's Marshall Space Flight Center. He is proposing that a multi-propulsion platform be attached to the International Space Station.
"We could test every one of the electric propulsion concepts that are on the table now, using the station as a laboratory," Chang-Diaz said. Doing so could save money and provide other benefits. Using vacuum test chambers on the ground is expensive. Further, each chamber has a mind of its own, introducing effects that can mask true levels of engine performance, he said.
Testing the VASIMR engine and its electric propulsion kin on the station would also help solve a serious and continuing problem up there -- reboosting the orbiting outpost into its proper position now and then after the atmosphere pulls it down.
"You'd be pushing on the station and overcoming the drag of the atmosphere," the astronaut said, adding that the process would create a more favorable level of microgravity for onboard science experiments.
A veteran of seven space shuttle flights, Chang-Diaz spotlights the utility of the giant complex: "The station is a beautiful laboratory. I was there. I saw it on the outside too. The station is something we can really take advantage of right now."
Nudging a nuisance
VASIMR is being looked at as candidate technology for other missions as well.
Last year, Chang-Diaz took part in a workshop on deflecting asteroids. Held at JSC, the workshop's goal was to brainstorm scenarios for altering an asteroid's orbit, perhaps using VASIMR powered by nuclear reactor.
The gathering included asteroid experts, engineers, current and former astronauts, and a Deep Space Network executive. Several participants advocated a nuclear electric plasma rocket as the best choice for a first demonstration mission.
How best to couple the engine to an asteroid was discussed. By exerting a continuous force -- on the order of one Newton, typical for a plasma engine powered by a 100-kilowatt electric source -- driving an asteroid was described as pushing a beach ball across a swimming pool using your nose.
Any asteroid deflection test using the rocket has spinoff advantages too.
For one, such a shakeout would be useful in flight-qualifying the technology for a suite of other missions, from supporting human flight to Mars to a fast-track flight to Pluto and beyond, into the Kuiper Belt.
Asteroid deflection work
A strong supporter of VASIMR is astronaut John Young, noting that the engine is ideal for planetary defense work. "This is new progress," Young said. "It's a great motor."
Young said JSC experts and others have begun discussing the idea of using VASIMR to shove a 230-foot (70-meter) asteroid around. Such practice runs could help hone scientists' ability to nudge potentially Earth-threatening asteroids out of harms way in the future, he said.
No asteroids are known to be on collision courses with Earth, but many experts have said planning should begin now for a method to destroy or deflect one that might one day be found to target the planet.
Young said VASIMR had its own near miss when the project was nearly cancelled. As Chang-Diaz and other crewmembers sat tucked inside Endeavour ready to start STS-111's climb toward the International Space Station in early June, NASA managers were ready to close down the project.
"The day he was going to launch they were going to shut his motor down and take away his people working on it," Young said. VASIMR was saved, but the project was given funding just through the rest of the year, he said.
"I think it's the motor that we ought to have," Young said. "If we're seriously talking about deflecting asteroids, that's the motor that will do it."
Eternal optimist
Protecting Earth from asteroids. Sending humans Marsward. Dispatching spacecraft outward into the depths of space -- these and other missions are constructive ways of using VASIMR technology, Chang-Diaz said.
VASIMR's promising attributes continue to be on trial. Future funding is in question, with the novel contraption entering a NASA limbo land of peer review later this year.
A thumbs-up would likely mean more cash would be pumped VASIMR's way to help harness the technology.
"We have been reviewed before. We'll do our best and go along. This is the way the game is played. And we want to be part of the team," Chang-Diaz said.
"I'm an eternal optimist," he concluded.
Build it and they will come? Test equipment is geared to demonstrate that VASIMR engine approach can thrust U.S. space program to new destinations. Credit: NASA/JSC
That's the ticket.
30 Newtons of thrust at 300 KM/s velocity, that's incredible performance, especially for a first generation design.
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.
This has me a little confused. Could you explain how this works and why it would be important?
I fully understand why a low thrust (mass) and high specific impulse (high velocity) is important, since velocity is squared in the equation.
What had me confused is why lowering the velocity and increasing the mass (fuel expended) would be an advantage. It seems to me that you would always want the highest velocity possible.
This is what had me confused. Perhaps I am missing something important here, and that is why I was asking for your help.
Work is the amount of force over a given amount of time. An Atomic Bomb releases a tremendous amount of energy in just a few milli-seconds and is obviously very powerfull.
However, the energy generated by a river over a period of a year, makes an Atomic Bomb look like nothing.
This article was confusing for this reason. It failed to explain how this new engine could "switch gears" and why that may be important.
Thanks for your help.
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