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.Glaser, P. E., Maynard, O. E., Mockovciak, J., and Ralph, E. L, Arthur D. Little, Inc., "Feasibility study of a satellite solar power station", NASA CR-2357, NTIS N74-17784, February 1974
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).Statement of John C. Mankins U.S. House Subcommittee on Space and Aeronautics Committee on Science, Sep 7, 2000 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 Assessmenthttp://www.nss.org/settlement/ssp/library/1981NASASPS-PowerTransmissionAndReception.pdf "Satellite Power System Concept Development and Evaluation Program: Power Transmission and Reception Technical Summary and Assessment" NASA Reference Publication 1076, July 1981. 281 pages. Space Transportation
Discontinuation
The project was not continued with the change in administrations after the 1980 United States elections. The Office of Technology Assessment concluded that "Too little is currently known about the technical, economic, and environmental aspects of SPS to make a sound decision whether to proceed with its development and deployment. In addition, without further research an SPS demonstration or systems-engineering verification program would be a high-risk venture."
Besides cost, SBSP also introduces several technological hurdles, including the problem of transmitting energy from orbit. Since wires extending from Earth's surface to an orbiting satellite are not feasible with current technology, SBSP designs generally include the wireless power transmission with its associated conversion inefficiencies, as well as land use concerns for antenna stations to receive the energy at Earth's surface. The collecting satellite would convert solar energy into electrical energy, power a microwave transmitter or laser emitter, and transmit this energy to a collector (or microwave rectenna) on Earth's surface. Contrary to appearances in fiction, most designs propose beam energy densities that are not harmful if human beings were to be inadvertently exposed, such as if a transmitting satellite's beam were to wander off-course. But the necessarily vast size of the receiving antennas would still require large blocks of land near the end users. The service life of space-based collectors in the face of long-term exposure to the space environment, including degradation from radiation and micrometeoroid damage, could also become a concern for SBSP.
As of 2020, SBSP is being actively pursued by Japan, China, Russia, India, the United Kingdom, the US, and the European Space Agency.
In 2008, Japan passed its Basic Space Law which established space solar power as a national goal. JAXA has a roadmap to commercial SBSP.
In 2015, the China Academy for Space Technology (CAST) showcased its roadmap at the International Space Development Conference. In February 2019, Science and Technology Daily (科技日报, Keji Ribao), the official newspaper of the Ministry of Science and Technology of the People's Republic of China, reported that construction of a testing base had started in Chongqing's Bishan District. CAST vice-president Li Ming was quoted as saying China expects to be the first nation to build a working space solar power station with practical value. Chinese scientists were reported as planning to launch several small- and medium-sized space power stations between 2021 and 2025. In December 2019, Xinhua News Agency reported that China plans to launch a 200-tonne SBSP station capable of generating megawatts (MW) of electricity to Earth by 2035.
In 1997, NASA conducted its "Fresh Look" study to examine the modern state of SBSP feasibility. In assessing "What has changed" since the DOE study, NASA asserted that the "US National Space Policy now calls for NASA to make significant investments in technology (not a particular vehicle) to drive the costs of ETO [Earth to Orbit] transportation down dramatically. This is, of course, an absolute requirement of space solar power."
Conversely, Pete Worden of NASA claimed that space-based solar is about five orders of magnitude more expensive than solar power from the Arizona desert, with a major cost being the transportation of materials to orbit. Worden referred to possible solutions as speculative and not available for decades at the earliest.
On November 2, 2012, China proposed a space collaboration with India that mentioned SBSP, "may be Space-based Solar Power initiative so that both India and China can work for long term association with proper funding along with other willing space faring nations to bring space solar power to earth."
Exploratory Research and Technology program
In 1999, NASA initiated its Space Solar Power Exploratory Research and Technology program (SERT) for the following purposes:Space Solar Power Satellite Technology Development at the Glenn Research Center—An Overview James E. Dudenhoefer and Patrick J. George, NASA Glenn Research Center, Cleveland, OhioReinventing the Solar Power Satellite", NASA 2004-212743, Geoffrey A. Landis, NASA Glenn Research CenterJ. Howell and J.C. Mankins, "Preliminary results from NASA's Space Solar Power Exploratory Research and Technology Program," 51st International Astronautical Congress, Rio de Janeiro, Brazil, 2000H. Feingold and C. Carrington, "Evaluation and comparison of space solar power concepts," 53rd International Astronautical Federation Congress. Acta Astronautica. Vol. 53, 4–10, August–November 2003, pp. 547–559.
Perform design studies of selected flight demonstration concepts. Evaluate studies of the general feasibility, design, and requirements. Create conceptual designs of subsystems that make use of advanced SSP technologies to benefit future space or terrestrial applications. Formulate a preliminary plan of action for the U.S. (working with international partners) to undertake an aggressive technology initiative. Construct technology development and demonstration roadmaps for critical space solar power (SSP) elements.
SERT went about developing a solar power satellite (SPS) concept for a future gigawatt space power system, to provide electrical power by converting the Sun's energy and beaming it to Earth's surface, and provided a conceptual development path that would utilize current technologies. SERT proposed an inflatable photovoltaic gossamer structure with concentrator lenses or solar heat engines to convert sunlight into electricity. The program looked both at systems in Sun-synchronous orbit and geosynchronous orbit. Some of SERT's conclusions:
The increasing global energy demand is likely to continue for multiple decades resulting in new power plants of all sizes being built. The environmental impact of those plants and their impact on world energy supplies and geopolitical relationships can be problematic. Renewable energy is a compelling approach, both philosophically and in engineering terms. Many renewable energy sources are limited in their ability to affordably provide the base load power required for global industrial development and prosperity, because of inherent land and water requirements. Based on their Concept Definition Study, space solar power concepts may be ready to reenter the discussion. Solar power satellites should no longer be envisioned as requiring unimaginably large initial investments in fixed infrastructure before the emplacement of productive power plants can begin. Space solar power systems appear to possess a number of significant environmental advantages when compared to alternative approaches. The economic viability of space solar power systems depends on multiple factors and the successful development of various new technologies (not least of which is the availability of much lower cost access to space than has been available); however, the same can be said of other advanced power technologies options.