You might expect to find our brightest hope for sending astronauts to other planets in Houston, at NASA’s Johnson Space Center, inside a high-security multibillion-dollar facility. But it’s actually a few miles down the street, in a large warehouse behind a strip mall. This bland and uninviting building is the private aerospace start-up Ad Astra Rocket Company, and inside, founder Franklin Chang Díaz is building a rocket engine that’s faster and more powerful than anything NASA has ever flown before. Speed, Chang Díaz believes, is the key to getting to Mars alive. In fact, he tells me as we peer into a three-story test chamber, his engine will one day travel not just to the Red Planet, but to Jupiter and beyond.

I look skeptical, and Chang Díaz smiles politely. He’s used to this reaction. He has been developing the concept of a plasma rocket since 1973, when he become a doctoral student at the Massachusetts Institute of Technology. His idea was this: Rocket fuel is a heavy and inefficient propellant. So instead he imagined building a spaceship engine that uses nuclear reactors to heat plasma to two million degrees. Magnetic fields would eject the hot gas out of the back of the engine. His calculations showed that a spaceship using such an engine could reach 123,000 miles per hour—New York to Los Angeles in about a minute.

Chang Díaz has spent nearly his entire career laboring to convince anyone who would listen that his idea will work, but that career has also taken several turns in the process. One day in 1980, he was pitching the unlimited potential of plasma rockets to yet another MIT professor. The professor listened patiently. “It sounds like borderline science fiction, I know,” Chang Díaz was saying. Then the telephone rang. The professor held up a finger. “Why, yes, he’s right here,” the surprised engineer said into the receiver, then handed it over. “Franklin, it’s for you.” NASA was on the line. The standout student from Costa Rica had been selected to become an astronaut, the first naturalized American ever chosen for NASA’s most elite corps. “I was so excited, I was practically dancing,” Chang Díaz recalls. “I almost accidentally strangled my professor with the telephone cord.”

All astronauts have big dreams, but Franklin Chang Díaz’s dreams are huge. As a college student, as a 25-year astronaut and as an entrepreneur, his single animating intention has always been to build—and fly—a rocketship to Mars. “Of course I wanted to be an astronaut, and of course I want to be able to fly in this,” he says of his plasma-thrust rocket. “I mean, I just can’t imagine not flying in a rocket I would build.” And now he’s close. In four years Chang Díaz will deploy his technology for the first time in space, when his company, aided by up to $100 million in private funding, plans to test a small rocket on the International Space Station. If this rocket, most commonly known by its loose acronym, Vasimr, for Variable Specific Impulse Magnetoplasma Rocket, proves itself worthy, he has an aggressive timetable for constructing increasingly bigger plasma-thrust space vehicles.

Chang Díaz describes his dreams in relatively practical terms. He doesn’t intend to go straight to Mars. First he will develop rockets that perform the more quotidian aspects of space maintenance needed by private companies and by the government: fixing, repositioning, or reboosting wayward satellites; clearing out the ever-growing whirl of “space junk” up there; fetching the stuff that can be salvaged. “Absolutely, fine, I’m not too proud to say it. We’re basically running a trucking business here,” he says. “We’ll be sort of a Triple-A tow truck in space. We’re happy to be a local garbage collector in space. That’s a reliable, sustainable, affordable business, and that’s how you grow.”

Eventually, though, Chang Díaz intends to build more than an extraterrestrial trucking business, and his ambitions happen to coincide with Barack Obama’s call for a privatized space industry that supports exploration well beyond the moon. “We’ll start by sending astronauts to an asteroid for the first time in history,” Obama said in a major NASA-related address earlier this year at Kennedy Space Center. “By the mid-2030s, I believe we can send humans to orbit Mars and return them safely to Earth.”

Such a belief may seem overly ambitious, but the goals of aviation have always seemed that way. In October 1903, for instance, astronomer Simon Newcomb, the founding president of the American Astronomical Society, spelled out a series of reasons why the concept of powered flight was dubious. “May not our mechanicians,” he asked, “be ultimately forced to admit that aerial flight is one of the great class of problems with which man can never cope, and give up all attempts to grapple with it?” Less than two months later, the Wright brothers flew at Kitty Hawk. And in the 1920s a young man named Frank Whittle was coming up with drawings for a theoretical engine very different from the propeller-driven kind, one that might scoop in air through turbines and fire it through a series of “jet” nozzles. “Very interesting, Whittle, my boy,” said one of his professors of aeronautical engineering at the University of Cambridge. “But it will never work.”

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