Deep Space 1 was designed as a test bed for several futuristic technologies, and now that it has shown that ion propulsion works, researchers at JPL are turning some of their attention to what may be the ultimate use of the technology: spacecraft so small and inexpensive that they are essentially disposable.

Each mini-spacecraft would be wrapped in solar cells and pack a small camera or other instruments needed to study the rings. An ion engine the size of a stamp would nudge each probe into a different part of the rings.

A similar method could deploy small probes all over the surface of Mars, dramatically increasing the coverage of a mission designed to measure winds, temperature or the chemical composition of the soil.

Ion technology is one of a handful of "electrical propulsion" systems that might one day power such tiny probes.

Colleen Marrese works in the same lab as Brophy, but she spends her day working on things too small to see.

Using "field emission cathode" technology similar to what lights up a flat-panel computer screen, Marrese is helping to develop efficient microscale cathodes for very small propulsion systems. Some of these systems would fit into a square the size of a postage stamp -- to give a small but adequate impetus to a miniature spacecraft.

Some 50,000 tiny cones are deposited on one square millimeter of a silicon wafer. Each cone is about one micron tall (a human hair is about 50 microns thick) and pokes out through a small aperture, leaving a gap all around the cone of about half a micron.

A voltage of 50 volts is applied across the gap, from the cone to the aperture. In such a small distance, this voltage creates a strong electrical field compared to the surrounding space. The high electric field allows electrons to tunnel out of the tips into the vacuum.

Other researchers at JPL are working on ways to harness these electrons to produce a small thrusters.

This overall micro-propulsion effort at JPL is headed up by Juergen Mueller, and in addition to Marrese's work, there are several thrusters and propulsion system components under development. Marrese anticipates that microscale electric thrusters will be developed enough to qualify for a mission in about two years.

Funding for such a mission would then be needed to polish off the engine technology.

If the technology that Mueller, Marrese and their colleagues are working on flies, John Brophy will likely have something to do with it.

"Part of my job is to try to get ion propulsion on every mission that JPL flies," he says.

Brophy, like many technologists here, is a scientist at heart. Given his druthers, he would spend most of his time tinkering with new ideas, working side-by-side with researchers like Marrese. But this is JPL, and scientists here are a part of the space program. They design and build spacecraft, they manage teams of workers, and above all else they must sell their ideas to JPL management and to NASA headquarters, which doles out 90 percent of JPL's funds.

The unusual mix is the one of the main reason scientists come to JPL and work for less money than they could get at a private institution.

"There's nowhere else you can work where one day you're trying to figure out how to catch up with a comet so you can land it, and the next day you're talking about returning samples from Mars," Brophy says.

But the required multitasking, along with a large bureaucracy, also frustrates many JPL employees. Brophy has now managed to sidestep much of this. The key: Someone else runs the lab he works in.

"I get to do whatever the heck I want without having to worry about all of the institutional problems that are associated with running a laboratory."

That does not mean Brophy is divorced from the often lengthy and complicated process that determines what flies, and therefore which teams get money. In fact, he admits to lately spending the bulk of his time in an office trying to secure the funding that helps keep the lab going.

He would like to see ion propulsion power spacecraft that would explore the edge of the solar system. Or power a human mission to Mars. An ion engine might even be chosen to fuel humanity's first push toward another star.

But while Brophy might be a dreamer, he's also a blunt tactician. He figures the best next chance for ion propulsion will be a mission to explore the asteroid belt between Mars and Jupiter, one that is in no rush and needs a cheap propulsion solution. So he prepares sales pitches. Fills out paperwork.

The effort is sometimes a crap shoot, since many missions are proposed by JPL and few are chosen by NASA headquarters.

"So far, we've been successful in getting on a lot of missions that JPL isn't going to fly," he said. "But it's only a matter of time before JPL flies another mission using ion propulsion."