Nasa making a more powerful ion engine (NEXT). NEXT can generate a force of 236 milliNewtons, compared to NSTAR's maximum of 92 mN. This corresponds to 6.9 kilowatts of engine power, compared to NSTAR's 2.3 kilowatts. A mission to Titan would take 20 kilowatts of engine power. An array of three NEXT engines plus a spare would be used. The engine was built by Aerojet, an aerospace company based in Sacramento, California, US.
Past article on space technology including the DS4G, european ion engine project
A second phase Nasa Institute of Advanced Concepts studies is further developing the idea of using Scalable Flat-Panel Nanoparticle MEMS/NEMS Propulsion Technology. It is very efficient at a braod range of ISPs (100-10,000 seconds)