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The plasma rocket, says U.S. astronaut Franklin Chang-Díaz, is the propulsion technology of the future.

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HE BUILT HIS FIRST ROCKET WHEN HE WAS SEVEN. It was a big cardboard box, fueled with the imagination of a Costa Rican boy who in October 1957 went to great heights for a closer look at Sputnik: He climbed a mango tree. From his perch, the satellite that launched the space race was a twinkling star racing past all the others in the heavens. Franklin Chang-Díaz knew then that his future was in physics. “I wanted to be like Wernher von Braun and Robert Goddard,” he says. “I wanted to design rockets.” That he spoke no English and lived in a country with no space program were inconveniences, not obstacles, to the young student, who eventually worked his way to the United States, immersed himself in the language, became a citizen, and made his dreams come true as an American astronaut.

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The boy who climbed the mango tree is now 53. He has been to space seven times, and, probably more than most astronauts, he ponders the fact that in nearly half a century, not much has changed about the way humans get there. They still rely on rockets that use chemical combustion and travel no faster than the missiles that carried the first astronauts into Earth orbit. The chemical combustion rocket “has given us the capability to go to the moon and establish a permanent presence in space, but it cannot go farther than it already has,” he says. “If we are going to do any serious exploration of the solar system, we have to develop a new type of propulsion that increases performance by orders of magnitude.”

Today, one of the most controversial proposals for a new type of propulsion is a product of Chang-Díaz’s imagination. His Variable Specific Impulse Magnetoplasma Rocket is one exotic cardboard box. Rather than burning liquid or solid rocket fuel, VASIMR would use radio waves to heat a stream of ionized gas, or plasma, which would then be expelled at terrific speeds. VASIMR’s exhaust nozzle is an electromagnetic field that can change shape to change the rocket’s speed. The concept borrows heavily from technology developed through years of research on controlled fusion.

VASIMR’s promise is that it could get to Mars in four months, half the time conventional rockets would need. Closer to home, the rocket could recycle waste hydrogen from the International Space Station to keep the lab in orbit without fuel deliveries from Earth. Chang-Díaz calls it a quantum leap in space transportation; “I am very much convinced that this is the way we’re going to go to Mars,” he says matter-of-factly.

With his passion and charm, the astronaut has convinced a fair number of experts that he’s on the right track. Many scientists, though, question whether the rocket will ever get off the ground. Partly out of professional courtesy, and partly for fear of jeopardizing their own NASA funding, those contacted for this article would not attach their names to specific criticism. But the complaints have a common theme: VASIMR continues to win more than its fair share of scarce research money, even though it has yet to produce what critics consider measurable results. One plasma scientist who is intimately familiar with the project goes even further: “VASIMR does not work, even on paper.”

Of course, no one is heading to Mars any time soon, so NASA can afford to gamble on ideas that may not ultimately pay off. The agency is putting nearly all its money for advanced space transportation into nuclear-powered ion-drive engines, under the heading of Project Prometheus (see “NASA Goes Nuclear,” June/July 2003). Only a pittance—meaning tens of millions of dollars in NASA’s $15 billion annual budget—goes to fund far-off, conceptual studies of propulsion methods, which range from solar sails to space elevators to VASIMR.

Chang-Díaz has scraped by for a decade with roughly the same amount of money every year—$1 million, give or take a few hundred thousand dollars. He has gotten some funding from NASA, including the astronaut office, and scrounged the rest wherever he could—the Department of Defense, other government agencies, research foundations, academic collaborators. He has established scientific liaisons with Department of Energy fusion researchers and with international institutions like the Australian National University, the Alfven Laboratory in Sweden, and the Center for High Technology of Costa Rica. John Mankins, who directs a NASA headquarters office called THREADS—Technology for Human/Robotic Exploration and Development of Space—says that perseverance as much as anything explains why the project is still alive: “VASIMR has persisted because Franklin has been a champion of it.”

The astronaut’s critics agree. They say Chang-Díaz is pursuing what amounts to a government-subsidized hobby. Says one: “It’s a big waste of taxpayer money to have all those beautiful toys and no scientific output to speak of.”

The output in question is thrust. If VASIMR had produced just a little, the critics say, they might think differently. Chang-Díaz claims that since it would be impractical to put the rocket in a test stand, its thrust is difficult to measure. Nevertheless, his team recently did measure a force of six or seven milli-newtons (about the same thrust that conventional ion drives produce) on a small target placed in the exhaust stream of his prototype engine, presently at the Johnson Space Center in Houston. That ought to be enough for now, he says, to prove that the concept works.

Chang-Díaz had hoped to mount a demonstration on the space station this year to show how VASIMR could be used to boost the station. But a panel of outside peer reviewers concluded that the system wasn’t ready for a flight test. So for now, it’s back to the lab, where VASIMR has been for nearly 20 years.

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