It is months beyond its life expectancy. Its power source is unlimited. Its fuel is plucked from the air we breathe. And it is 10 times more efficient than a chemically powered engine.

This is rocket science for a new millennium.

It is called an ion thruster. No pipe-dream technology, this test engine in a JPL vacuum chamber is a twin of the one powering the Deep Space 1 spacecraft, which has logged more than 167 million miles (269 million kilometers) in space since its launch on Oct. 24, 1998.

John Brophy, an engineer who has worked on the ion engine since 1984, heads up a hill on the JPL campus toward Building 148 where he works in every day. As he walks he explains that he and his colleagues are working to develop tiny versions of the ion engine, thrusters no larger than a postage stamp that could power spacecraft the size of soup cans.

"You might fly a whole bunch of little satellites into the rings of Saturn," he explains. "It's a very hazardous environment. Some might get destroyed. But that would not be as disastrous as loosing a much more expensive, full-sized spacecraft."

Because they would be relatively cheap and plentiful.

Letters on the side of Building 148 proclaim it to be the Energy Conversion Laboratory. Asked what that means, Brophy looks puzzled, as though he's never noticed the name before. "That's a really old name," he says, and shrugs.

The past decade has been one of great change at JPL. Instead of launching one or two large missions per decade, the robotics institute now plans multiple missions each year. "Better, faster, cheaper," an overall NASA initiative, is the guiding principle. And the constant cycling of activity means everything on this 177-acre complex is remade over and over. Computers, storage racks, buildings and scientists are shifted from completed missions to new projects.

John Brophy is an exception. He's been working pretty much on one thing -- ion propulsion -- for 17 years now, except for two brief periods when he left JPL for industry jobs that looked, at the time, more attractive. He came back both times. Why? In private industry, the goal is always to make money, he said, but "your principal objective here is to do cool things. I keep coming back because this is by far the best place to work, but that's from the perspective of having left a few times."

Brophy opens the door to Building 148, a door the future of space travel.