According to Escape Dynamics, "the key operational components of the microwave beam power launch system are a ground-based microwave array and an engine based on the heat exchange between the hydrogen propellant and the incoming microwave radiation. Hydrogen heating is achieved with the heat exchanger, which heats the propellant to a temperature above 2,000 [degrees Kelvin], which is necessary for efficient operation of the engine."
To be sure, the idea of using beamed energy to get a rocket off the ground is nothing new. Parkin said that Russian rocket scientist Konstantin Tsiolkovsky first proposed the idea in 1924. But back then, Parkin added, there was no such thing as beams or lasers, let alone those powerful enough to launch a vehicle into space.