Space applications of high power microwaves

A variety of methods have been suggested for transferring energy from Earth-to-space, space-to-Earth, and space-to-space using high power microwave beams. All use power beaming. Microwave beams have been studied for propelling spacecraft for launch to orbit, orbit raising, launch from orbit into interplanetary and interstellar space and deployment of large space structures. The microwave thermal rocket, called the ‘microwave thermal thruster’, is a reusable single stage vehicle that uses a high power microwave beam to provide power to a heat-exchanger propulsion system, with double the specific impulse of conventional rockets. It could transform the economics of launch to space. Microwave propelled sails are a new class of spacecraft that promises to revolutionize future space probes. Beam-driven sail flights have now demonstrated the basic features of the beam-driven propulsion. An early mission for microwave space propulsion is dramatically shortening the time needed for sails to escape Earth orbit. Simulations of trajectories and escape time for sails driven by a microwave beam from the surface or from orbit show that resonance methods can reduce escape times from Earth orbit by as much as two orders of magnitude. A number of missions for beam-driven sails have been quantified for high velocity mapping of the outer solar system, Kuiper Belt, the Heliopause, the interstellar medium. The penultimate is the interstellar precursor mission. For this mission class, operating at high acceleration the sail size can be reduced to less than 100 m and accelerating power ∼100 MW focused on the sail. At 1 GW, sail size extends to 200 m and super-lightweight probes reach velocities of 250 km/s for very fast missions. Will such sails riding beams be stable? Experiments and simulations have verified that beam-riding does occur for conical sail shapes. Beams can also carry angular momentum and communicate it to a sail to help control it in flight. Although technical feasibility is the focus here, advocates must also deal with societal issues: interference with unintended targets in the sidelobes, spectrum allocation and potential weaponization. Much of the technical means are already in hand: microwave and millimeter wave array antennas are already in use for astronomy, sources at high frequencies are being developed for fusion and the military. A synergistic way to develop a space power-beaming infrastructure is incremental buildup based on a common module, with lower power applications addressed first, followed by steady upgrading to higher power, larger apertures.