NASA is big on solar electric propulsion (the Dawn spacecraft uses it, for instance) for a good reason: while the engines aren't powerful, they supply thrust for a very long time before giving up the ghost. And it now looks like the agency is ready to double down on that super-efficient tech. It just awarded a $67 million, 3-year contract to Aerojet Rocketdyne in hopes of developing an advanced solar electric propulsion system. The new technology could deliver twice as much thrust, and would be up to 10 times more efficient than chemical engines -- both big deals for deep space missions.