Following World War II, which saw the development of high-power microwave emitters known as cavity magnetronss, the idea of using microwaves to transmit power was researched. However, while electricity could be converted to microwaves in a magnetron, no method was known for converting microwaves back into electricity. Then, in 1964, William C. Brown demonstrated a helicopter equipped with a device called a rectenna. The rectenna converted microwave power into electricity, allowing the helicopter to fly.
Following the oil crises of the 1970s, NASA researched power transmission via microwaves and developed the idea of the solar power satellite (SPS). The MPT approach could theoretically allow solar collection satellites orbiting near the sun to collect solar energy. Since light intensity decreases by the inverse-square law, placing the satellites closer to the sun would increase their effective area for collecting solar energy. Energy would be beamed to ground receiving stations on earth to be transformed directly (without the use of a turbine, due to it already being an electromagnetic form of energy) into electrical power.
Another SPS approach would involve a large satellite (5km by 20km, 50,000 tons) with solar cells (Si or GaAlAs) in geostationary orbit (36,000km above the Earth). It could generate 5 to 10 gigawattss of power. However, many technological issues would have to be overcome before the SPS could be realized. Microwave power would need to be transmitted with high efficiency, high levels of safety would have to be maintained, and scientific analysis of the impact of microwaves on the space plasma environment as well as the Earth's atmosphere would have to be undertaken.