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.
History
In 1941, science fiction writer Isaac Asimov published the science fiction short story "Reason", in which a space station transmits energy collected from the Sun to various planets. Solar panels on spacecraft have been in use since 1958, when Vanguard I used them to power one of its radio transmitters; however, the term (and acronyms) above are generally used in the context of large-scale transmission of energy for use on Earth. The SBSP concept, originally known as satellite solar-power system (SSPS), was first described in November 1968. In 1973 Peter Glaser was granted U.S. patent number 3,781,647 for his method of transmitting power over long distances (e.g. from an SPS to Earth's surface) using microwaves from a large antenna (up to one square kilometer) on the satellite to a much larger one, now known as a rectenna, on the ground. Glaser then was a vice president at Arthur D. Little, Inc. NASA signed a contract with ADL to lead four other companies in a broader study in 1974. They found that, while the concept had several major problems – chiefly the expense of putting the required materials in orbit and the lack of experience on projects of this scale in space – it showed enough promise to merit further investigation and research.
Concept development and evaluation
Between 1978 and 1986, the Congress authorized the Department of Energy (DoE) and NASA to jointly investigate the concept. They organized the Satellite Power System Concept Development and Evaluation Program. The study remains the most extensive performed to date (budget $50 million). Several reports were published investigating the engineering feasibility of such a project. They include:
Resource Requirements (Critical Materials, Energy, and Land) Financial/Management Scenarios Public Acceptance State and Local Regulations as Applied to Satellite Power System Microwave Receiving Antenna Facilities Student Participation Potential of Laser for SBSP Power Transmission International Agreements Centralization/Decentralization Mapping of Exclusion Areas For Rectenna Sites Economic and Demographic Issues Related to Deployment Some Questions and Answers Meteorological Effects on Laser Beam Propagation and Direct Solar Pumped Lasers Public Outreach Experiment Power Transmission and Reception Technical Summary and Assessment Space Transportation
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