Engineers from the European aerospace company Airbus demonstrated what the potential future of sustainable energy would look like late last month in Munich. They used solar panels to capture sunlight, then converted it into microwaves to beam the energy across an airplane hangar, where it was converted back into electricity that, among other things, illuminated a model city. The demonstration only produced 2 kilowatts of power over a distance of 36 meters, but it prompted a serious inquiry: Is it time to revive a plan that was long dismissed as science fiction and deploy massive satellites to gather solar energy in space? They could produce power around-the-clock and beam it down to Earth from a high orbit, where they would be free from clouds and the dark.

Jean-Dominique Coste, an engineer with Airbus, claims that the issue is not a recent development in science. The critical need for green energy, more affordable access to space, and advancements in technology, however, may ultimately change that, according to advocates of space solar power. “It will blossom once someone makes the commercial investment. According to former NASA researcher John Mankins, who assessed space solar power for the organization a decade ago, it may become a trillion-dollar business.

Numerous uncertainties remain, including whether beaming gigawatts of power down to the globe can be done effectively—and without burning birds, if not people. Major expenditures are probably far in the future. However, concept papers are giving way to more and more ground and space testing as the idea. The European Space Agency (ESA), which funded the Munich demonstration, would recommend to its member states a series of ground experiments the following month to determine the feasibility of the plan. The U.K. This year, the government provided grants worth up to £6 million to explore new technology. Agencies from China, Japan, South Korea, and the United States are all making modest efforts. According to Nikolai Joseph, author of an analysis NASA expects to disclose in the coming weeks, “the tone and tenor of the entire discourse has shifted.” Space policy expert Karen Jones of Aerospace Corporation claims that what formerly looked unachievable may now only require “bringing it all together and making it work.”

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During the fuel crisis in the middle of the 1970s, NASA began to look into the idea of solar power in space. A projected space demonstration trip, however, would have cost approximately $1 trillion and used equipment from the 1970s that was lofted in the Space Shuttle and put together by humans. The plan was abandoned, and many agency employees still view it as taboo, according to Mankins. The state of solar and space technologies today is unrecognizable. According to Jones, photovoltaic (PV) solar cells’ efficiency has grown 25% over the last ten years despite their costs falling. In the telecom sector, microwave transmitters and receivers are a well-established technology. Robots that are being created to maintain and refuel satellites in orbit may one day be used to construct enormous solar arrays.

But decreasing launch costs have given the concept the largest push. It would take hundreds of launches to launch a solar power satellite large enough to replace a standard nuclear or coal-powered station. According to Sanjay Vijendran, an ESA space scientist, “it would necessitate a large-scale building site in orbit.” The idea has become less far-fetched thanks to the private space corporation SpaceX. Less than 5% of what it cost aboard the Space Shuttle, a SpaceX Falcon 9 rocket can loft cargo for only $2600 per kilogram. The company also offers prices of under $10 per kilogram for its enormous Starship, which is scheduled to fly for the first time this year. It is altering the equation, according to Jones. Economics is fundamental.

Similarly, space hardware is becoming less expensive because to mass manufacture. Typically, satellites are unique creations made from pricey space-rated parts. For instance, the Perseverance rover from NASA cost $2 million per kilogram. For less than $1000 per kilogram, SpaceX can produce its Starlink communication satellites. Mankins, who is currently at the consultancy Artemis Innovation Management Solutions, has long believed that technique may work for enormous space structures built of countless numbers of identical low-cost components. He claims that when low-cost launches are combined with this “hypermodularity,” “suddenly the economics of space solar power become evident.” Better engineering might improve those economics. Comparing the amount of solar energy intake with the amount of power production, Coste claims that Airbus’ demonstration in Munich was 5% overall efficient. However, only when the Sun is shining do ground-based solar arrays perform better. According to recent studies, space solar might compete with conventional energy sources on price if it can reach 20% efficiency.

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The cost calculation will also be improved by lighter components. Pizza box-sized “sandwich panels,” which have microwave transmitters, electronics, and PV cells on opposite sides, might be useful. The foundation of a space solar satellite can be created by connecting thousands of these like tiles without using a lot of bulky cabling to transfer power. For years, scientists have tested prototypes in real-world settings, but in 2020 a team at the U.S. Aboard the X-37B experimental spacecraft of the Air Force was the Naval Research Laboratory (NRL). According to project manager Paul Jaffe of NRL, “It’s still in orbit, providing data the entire time.” The panel converts solar energy into microwaves with an efficiency of 8% but does not transmit them to Earth. The Air Force, though, intends to test a sandwich panel that will shoot its energy downward next year. Additionally, a California Institute of Technology team will use SpaceX to launch its prototype panel in December.

Sandwich panels have the disadvantage that the microwave side must constantly face Earth, causing the PV side to occasionally turn away from the Sun as the satellite orbits. A satellite will need mirrors to keep that side lit in order to sustain 24-hour power, with the added benefit that the mirrors can also focus light onto the PV. A bowl-shaped device with thousands of individually steerable thin-film mirrors was proposed in a 2012 NASA study by Mankins as a way to focus light onto the PV array. An alternative strategy has been devised by Ian Cash of the International Electric Company in the United Kingdom. In order to maintain the mirrors pointed toward the sun, his planned satellite uses enormous, stationary mirrors that are oriented to deflect light onto a PV and microwave array (see graphic, above). One billion tiny perpendicular antennas form a “phased array” using the microwave energy from the PV cells to electronically guide the beam toward Earth regardless of the orientation of the satellite. According to Cash, this design is “the most competitive economically” since it offers the greatest power to weight ratio.

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If a space-based power station ever takes flight, the energy it produces must be transported to the earth effectively and securely. Jaffe’s team at NRL beamed 1.6 kilowatts across a kilometer in a recent ground-based test, and teams in Japan, China, and South Korea have made comparable efforts. But the input power of modern transmitters and receivers is lost by half. According to Vijendran, power beaming from space solar needs an efficiency of 75%, with a goal of 90%. It also has to be tested whether beaming gigawatts through the atmosphere is safe. The majority of designs aim to create a beam that is kilometers broad so that any errant objects—such as a person, bird, or spacecraft—will only be exposed to a small, hopefully harmless piece of the 2-gigawatt transmission. Although you could grow vegetables under them or put them offshore, Jones claims that although receiving antennas are inexpensive to install, they “require a lot of real estate.”

Public institutions are currently paying the most attention to space solar power in Europe. There is a devotion there that is lacking in the United States, according to Jones. ESA commissioned two cost-benefit analyses of space solar last year. It might be comparable in price to ground-based renewables, according to Vijendran. However, even at a greater cost, comparable to nuclear power, its 24/7 accessibility—in contrast to traditional solar or wind—would make it competitive. ESA will request funding from member states in November to fund a review of the technological challenges. If the report is favorable, the agency will outline preparations for a comprehensive endeavor in 2025. According to Vijendran, the ESA could launch a megawatt-size demonstration facility into orbit by 2030 and scale it up to gigawatts—the equivalent of a conventional power plant—by 2040 with a budget of €15 billion to €20 billion. It’s comparable to a moonshot.

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