Traditional chemical rockets may be a thing of the past. The dawn of "electric propulsion" is here (OK, enough hyperbole).
Aerojet has provided NASA with a new engine dubbed NASA's Evolutionary Xenon Thruster or simply, NEXT. NEXT is designed to provide three times the thrust of the previously used NSTAR ion thruster used on the Deep Space One mission. It will provide much greater fuel efficiency than NSTAR (+30%) and will require less than 10% of the propellant needed by conventional chemical rockets.
NASA views NEXT as an important step in the evolution of its deep space mission program.