An analysis of this innovative propulsion system credited to Jeff Greason of the Tau Zero Foundation is provided by Alex Tolley. The method for powering a starship saves fuel by extracting energy from plasma streams in the interstellar medium (or closer to home, from the solar wind) and converting it to momentum using onboard fuel to propel the ship. Although there are engineering challenges, the physics is sound and the savings in fuel enables the system to accelerate payloads to 20% of the speed of light.