Using rockets to launch satellites and people into orbit currently requires a lot of high-energy fuel, which is 95% of total rocket mass. Launching a pound of payload can cost $10,000 or more, so minimizing the total cost of launching rockets would maximize the scientific payloads and increase the feasibility of space exploration.
Researchers have solved important wireless power transmission and other efficiency issues that must be overcome to use high-powered microwaves to supplement — or nearly replace — chemical fuel for rocket launches. It is commonly believed that a rocket requires a megawatt of beam-powered propulsion — approximately the power output of 10 automobiles — per kilogram of payload to reach a minimal orbit. Whether microwave transmission is efficient for real-world applications is an open question.
Microwave beams have been transmitted using a ground antenna that is the same size as a rocket antenna. Practical applications will require a large ground-based transmitter and a small receiver on the rocket and thus, variable-focus transmission.
The researchers calculated the efficiencies, at short distances, of a ground-based microwave generator wireless power supply that sends the microwaves to the rocket propulsion system, receiving antenna on the rocket, and propulsion device that uses the microwave energy to heat the rocket propellant. Researchers can now put numbers on how efficient variable-focus transmission is at present.
Future research will study and improve efficiencies at long distances. This is an important next step in advancing microwave technology to practical use in rocket launches.