Space-based solar power

Space-based solar power (SBSP or SSP) is the concept of collecting solar power in outer space with solar power satellites (SPS) and distributing it to Earth. Its advantages include a higher collection of energy due to the lack of reflection and absorption by the atmosphere, the possibility of very little night, and a better ability to orient to face the Sun. Space-based solar power systems convert sunlight to some other form of energy (such as microwaves) which can be transmitted through the atmosphere to receivers on the Earth's surface.

In the 1970s, groups like the L5 Society promoted space-based solar power for civilian energy. They soon recognized the technology potential as a directed energy weapon for ballistic missile defense. This dual-use shaped the 1980s Strategic Defense Initiative (SDI)—whose prominent architects, including physicist Lowell Wood, were early L5 members. Orbital power generation and directed-energy transmission continue to receive funding for modern missile defense such as for the 2025 Golden Dome program.

In May 2020, the US Naval Research Laboratory conducted its first test of solar power generation in a satellite. In August 2021, the California Institute of Technology (Caltech) announced that it planned to launch a SBSP test array by 2023, and at the same time revealed that Donald Bren and his wife Brigitte, both Caltech trustees, had been since 2013 funding the institute's Space-based Solar Power Project, donating over $100 million. Caltech's MAPLE project successfully demonstrated beaming power to earth in 2023. MAPLE transmitted an effective isotropic radiated power (EIRP) of 3.2 watts (+35 dBm), far below the kilowatts typical of commercial communications satellites. The amount of power detected on the ground was about -45 dBm, or less than a tenth of a microwatt.