Hughes Electron Dynamics, a unit of Hughes Electronics Corp., manufactured the ion engine.

The engine has now completed more than 500 hours of operation after its successful start-up on Nov. 24, and the spacecraft is now more than 6 million miles from Earth.

"The ion propulsion system has already operated for a longer uninterrupted time on Deep Space 1 than we had planned for the entire mission," said Deep Space 1 Deputy Mission Manager and Chief Mission Engineer Dr. Marc Rayman of the Jet Propulsion Laboratory.

"I anticipate that the successful demonstration of this important technology on Deep Space 1 will pave the way for exciting missions throughout the solar system that would be unaffordable or impossible with conventional chemical propulsion."

Hughes, with NASA, began investigating ion engines back in the 1960s. At that time, gases such as cesium and mercury were under study, but xenon proved to be the best alternative to chemical bipropellants.

The NASA Solar Electric Propulsion Technology Application Readiness (NSTAR) 30-centimeter system is one type of ion engine. Hughes has also developed a commercial xenon ion propulsion system, XIPS, that is used on its HS 702 and HS 601HP communications satellites.

Four XIPS systems are currently on-orbit; a fifth was launched on board the Hughes-built PAS-6B on Dec. 21 and should begin operation in the coming months.

"The benefit of a xenon ion engine is its efficiency," said Tim Fong, general manager of Hughes Electron Dynamics.

"The ion engine, while very efficient, is slow to build speed. Some have likened it to the lesson of the tortoise and the hare. If you want to get there quickly, use a bipropellant. But if you have time to reach your destination, an ion engine is an efficient alternative since a reduction of propellant mass of up to 90 percent is possible, resulting in a lighter spacecraft.

"Deep Space 1's ion engine has the ability to increase the spacecraft speed by 10,000 miles per hour, yet will consume only 180 pounds of xenon, which would be 10 times more efficient than chemical propellant. Efficient, steady, constant -- these are the operational characteristics of an ion engine," Fong said.

There were other design considerations for the NSTAR ion engine. Unlike its commercial satellite cousins, it would be traveling in deep space with diminished exposure to the sun, and therefore less solar energy would be available to power the spacecraft. For that reason, the NSTAR ion engine is remotely programmable, allowing NASA to adjust its thrust to meet these changing conditions over the life of the mission.

"Ion engines are definitely the wave of the future," said Fong. "It's something that has been mentioned in science fiction for decades, but finally, it is reality. Hughes is proud of its association with the Jet Propulsion Laboratory and with NASA, and we thank them for allowing us to participate in this mission."