Editing Beam-powered propulsion (section)

==Microwave propulsion==
In microwave thermal propulsion, an external microwave beam is used to heat a refractory heat exchanger to >1,500 K, heating a propellant such as hydrogen, methane, or ammonia. This improves the propulsion system's specific impulse and thrust/weight ratio relative to conventional rocket propulsion. For example, hydrogen can provide a specific impulse of 700–900 seconds and a thrust/weight ratio of 50-150.<ref name="parkin">{{citation | last=Parkin | first=Kevin L.G. | title=The Microwave Thermal Thruster and Its Application to the Launch Problem | year=2006 | publisher=California Institute of Technology | doi=10.7907/T337-T709 | url=https://resolver.caltech.edu/CaltechETD:etd-06022006-160023}}</ref>

A variation, developed by brothers [[James Benford]] and [[Gregory Benford]], is to use thermal [[desorption]] of propellant trapped in the material of a massive [[Solar sail|microwave sail]]. This produces a very high acceleration compared to microwave-pushed sails alone.