Neat Tech: Radio Plasma Drive

NASA Ad Astra Ink Second Space Act Agreement in “Vasimr” Engine (subscription required)

NASA is working with Ad Astra Rocket Co. on it's Vasimr engine. It uses radio waves to heat electrically charged fluids to extremely high temperatures for fuel efficiency, controlling the resulting plasmas for thrust and insulating nearby structures with magnetic fields.

ISP appears to be in the 5K-12K seconds range (PDF), or more than 10 to more than 30x that of chemical rockets.

Unlike Ion, it's supposed to support higher thrust levels, on the order of 100+ N, compared to the millinewton levels for Ion drives.