Spacecraft Bridges Gap Between Science Fiction and Reality

With the launch this weekend of a spacecraft brimming with potentially revolutionary devices, NASA is taking its first steps into a technological realm previously open only to science fiction.

Deep Space 1, a tiny craft powered by an new type of engine conceived by a Russian in the 1920s, then featured prominently in the TV series "Star Trek," is the first in a series of spacecraft designed to put the space agency's newest, most risky innovations through the rigors of spaceflight.

The $152 million mission, part of the New Millennium program, is a part of NASA's effort to embrace smaller, more frequent projects in a time of shrinking federal budgets. And NASA officials are looking for new technologies to squeeze the most science out of the smallest packages.

The goal of the New Millennium program is to test devices that "hold more risk than the people who plan science missions would want to accept," says Arthur Amador, lead flight engineer for Deep Space 1 at CalTech's Jet Propulsion Laboratory in Pasadena, Calif.

Although Deep Space 1 will be testing a dozen new devices on its year-long mission - including a new navigation system that corrects itself - the craft's engine is taking center stage. Known as ion drive, the propulsion system has actually been around in various forms since 1959. The first commercial satellite to carry ion engines was launched in 1997, using the devices to steer itself in orbit.

But Deep Space 1, which will be conducting scientific surveys of an asteroid and a pair of comets, is the first craft to use the propulsion unit for interplanetary travel.

Ion propulsion uses xenon gas as a fuel - making it much lighter than chemical engines. A cathode in the engine shoots a beam of electrons, knocking other electrons off xenon atoms. Electrically charged grids at the rear of the engine draw all the free electrons to them, building a negative charge that attracts the positively charged xenon ions. Then the ions shoot past the grid at speeds in excess of 62,000 miles an hour, giving the engine its thrust.

The thrust is small, however, exerting as much force as a piece of paper resting on the palm of a hand. Yet the ion engine burns continuously, slowly building speed until the craft reaches its desired velocity.

The ion engine can deliver as much as 10 times more thrust for a given amount of fuel than a chemical rocket engine, says Vincent Rawlin, a senior researcher at NASA's Lewis Research Center in Cleveland. But it's not the best engine for delivering quick bursts of speed needed to launch a payload into orbit. That job still falls to more powerful chemical rockets.

In space, however, the Volkswagen-like ion engine can outrace and outlast its chemical Corvette counterparts, cutting two or three years off the flight time to Pluto, for example.

"It's like the tortoise and the hare," Mr. Amador says.