The new ion engine builds upon the electric propulsion systems used by both DS1 and Dawn, says Patterson. It uses the same method to achieve thrust: xenon gas flows into a reaction chamber inside the engine and is ionized by electrons; electromagnets positioned around this chamber enhance the efficiency of ionization. Electrodes positioned near the engine’s thrusters (known as ion optics) are then used to accelerate the ions electrostatically and shoot them out of the exhaust to push the spacecraft forward.

The Glenn Research Center engineers optimized the mechanical design of the engine’s magnets and ion optics, and made other modifications, including reducing the number of thrusters, to make the system more powerful and more efficient. “The engine has a higher power level and a larger throttling dynamic range–it can go from very high power to very low power–so it can operate for longer periods of time and better execute its mission,” says Patterson.

Michael Huggins, the space and missile propulsion directorate in the Air Force Research Laboratory at Edwards Air Force Base in California, says it is important to find ways to make propulsion systems more efficient, smaller, and more economical. The fact that NASA is looking at more-efficient devices for interplanetary missions “is definitely the right answer,” he says.

However, there are potential drawbacks to ionic propulsion. For example, solar energy cannot be used too far from the sun. “Solar just won’t work out to distances like Neptune,” says White, who presented a paper at the same conference on using nuclear energy as a power source for deep-space missions. While this would provide plenty of power in deep space, safety concerns would make it politically challenging to launch a nuclear-powered spacecraft.

“The only competitor we really have is advanced chemical technology,” says Patterson. “The advantage that we have is that we are very fuel efficient.” Thus, for complex planetary missions that require lots of energy, says Patterson, the US and its international partners, including Japan and European nations, are transitioning to ion propulsion engines.