An artistic depiction of sunlight-harvesting satellites supplying electricity from Earth orbit by beaming power to ground-based receiving stations.

By Leonard David

When inventor Charles Fritts created the first crude solar photovoltaic cells in the 1880s, one might have thought the achievement would rapidly revolutionize global electricity production. There is, after all, no power source cheaper, cleaner and more ubiquitous than sunlight. Yet despite enormous (and ongoing) technical advances making solar power ever more capable and affordable, some 140 years on it still supplies less than 5 percent of the world’s electricity. For all its benefits, solar power does have drawbacks that can limit its use—chief among them the fact that half the planet’s surface is in darkness at any given time.

In 1968 U.S. aerospace engineer Peter Glaser detailed a potential solution to these problems that was not only “outside the box” but entirely outside Earth’s atmosphere. Instead of building gigantic solar farms across vast, ecologically vulnerable tracts of land, Glaser proposed to loft the photovoltaics into orbit on fleets of solar power satellites. In orbit—unattenuated by clouds and freed from planetary cycles of day and night—sunlight could be harvested with optimum efficiency, then beamed as microwaves to ground-based “rectifying antennas” (rectennas). Back on Earth, the microwaves would be converted to electricity and channeled into power grids across the globe.

At the time and for decades afterward, however, the cost of space launches was too high and the performance of photovoltaics was too low to make Glaser’s bright idea a reality. But now technological advances, paired with the growing need for clean energy, are reinvigorating the concept of space-based solar power (SBSP), with pilot projects emerging in the U.S., China, Europe and Japan. As a new wave of research begins, the question lingers: Will SBSP ever be ready for its moment in the sun?

LEANING INTO THE FUTURE

In the U.S., spurred by rapid growth in the space industry and the dire threats from climate change, NASA is taking a close look at the current and near-future prospects for SBSP. Nikolai Joseph, a policy analyst at NASA’s Office of Technology, Policy and Strategy (OTPS), is lead author of a forthcoming OTPS study looking specifically into the approach. Given the rising global interest in the transformative possibilities of SBSP, it makes sense for OTPS to undertake a study now, he says.

“Space-based solar power has been attractive for decades, but building and launching spacecraft that could utilize it was seen as prohibitively expensive,” Joseph says. “Now technological developments and the growth of the space industry over the past decade may mean that’s changing…. It’s important to regularly revisit good ideas and investigate options. NASA needs to know what’s possible, as the advent of space-based solar power would intersect with many of our other interests. NASA needs to be following all aspects of space technology. We should always be leaning into the future.”

For NASA, that future could well entail use of SBSP beyond Earth, supporting the space agency’s burgeoning Artemis program of crewed lunar exploration. For instance, an SBSP capability around the moon could help empower outposts and other exploration activities on the lunar surface. More ambitiously, beamed power could also someday be used to send spacecraft to interplanetary and even interstellar destinations without the costly trouble of carrying along onboard propellant.

A POWER PANACEA?

Back on Earth, SBSP is seen by some as an ideal way to achieve net-zero greenhouse gas emissions while still having a steady, sustainable and plentiful power supply. Unlike electricity from ground-based solar and wind power—both of which are far more vulnerable to disruptions from fluctuating ambient conditions—SBSP could function around the clock (offering so-called baseload power) while also allowing agile, responsive distribution of electricity across and between power grids (“dispatchable” power).

“Uniquely, space-based solar power can provide both baseload and dispatchable power at city scale and as such is a really valuable new clean-energy technology,” says Martin Soltau, an analyst at Frazer-Nash Consultancy and co-chair of the U.K.’s Space Energy Initiative (SEI). “An additional advantage is that space-based solar power doesn’t need electricity grids to be reengineered. We envisage the ground [rectennas] being located near existing grid interconnections, potentially adjacent to existing offshore wind farms.” The SEI is a partnership between government, industry and academia seeking to build an SBSP fleet for linkage to the U.K. power grid in the 2040s. Each spacecraft in the SEI’s notional fleet would produce about as much electricity as a coal- or nuclear-fueled power plant.

For any of that to occur, though, robust rounds of in-space testing are required. That is why, well before a full SBPS fleet debuts, SEI intends to first launch an orbital demonstrator by 2030.

“Probably the two technologies most important to test and demonstrate in space early on are the autonomous robotic assembly of these large structures and beaming power from space to Earth at meaningful power levels,” Soltau says. “There are many other important issues that will need to be addressed, such as the regulatory environment and spectrum allocation,” he adds.

HIGH-TECH TESTING

SEI is not alone in pursuing real-world tests of SBSP-related hardware. Multiple projects to do so are underway throughout the globe.

The China Academy of Space Technology and Xidian University in China have erected a large structure to demonstrate new technologies for concentrating sunlight and for wireless power transmission. Codenamed Zhuri, or “Chasing the Sun,” the project uses a 75-meter-high steel towerbuilt at the south campus of Xidian University. The new facility is designed to test and verify technology for the Orb-Shape Membrane Energy Gathering Array (OMEGA), a concentrator system for harvesting solar power in geostationary orbit.

Then there’s the European Space Agency’s SOLARIS initiative, a proposed three-year research-and-development agenda to explore the SBSP concept and critical technologies. SOLARIS is being proposed for approval at ESA’s Council Meeting at Ministerial Level this November. On October 18 ESA held a “SOLARIS Industry Day” to sharpen SBSP research and development tasks that, if supported, can happen in the 2023–2025 time frame.

In Japan, investigators have been doggedly studying SBSP since the 1980s. Researchers at the Japan Aerospace Exploration Agency (JAXA) have devised a plan for developing and testing novel ways of controlling power beams and assembling large structures in orbit. Ideally, this work would lead to SBSP systems within a decade or two. Beyond paper appraisals, Japanese SBSP researchers have also fabricated technology to increase the accuracy of laser and microwave power beams and are flying SBSP-related gear on suborbital rockets to gather technical data.

Back in the U.S., outside of NASA and its civil space interests, the Department of Defense is also keenly interested in using SBSP to power military operations around the globe. The latest effort there, the U.S. Air Force Research Laboratory’s Space Solar Power Incremental Demonstrations and Research (SSPIDR) project, involves contributions from the aerospace company Northrop Grumman, as well as the U.S. Naval Research Laboratory (NRL). SPPIDR recently conducted the first ground-based test of equipment for an in-space flight experiment dubbed Arachne. Expected to launch in 2025, one of Arachne’s assignments is to demonstrate the ability to form and focus a radio-frequency beam in low-Earth orbit. The goal of this work is “to provide uninterrupted, assured, and logistically agile power to expeditionary forces,” according to the Air Force.

Meanwhile the NRL has pioneered specialized modules designed to boost the efficiency of converting solar energy into microwaves. A test apparatus incorporating them, called the Photovoltaic Radio-Frequency Antenna Module, even spent more than 900 days in space onboard the U.S. Air Force’s secretive X-37B robotic space plane.

EBBS AND FLOWS

Paul Jaffe, an NRL electronics engineer with a long history of SBSP-related work, says interest in the topic has ebbed and flowed across the years but that the current spike in projects is because of real, meaningful progress on critical enabling technologies.

“The historical objection to SBSP has been economics, principally the matter of launch cost,” Jaffe says. “I think the verdict is still out on whether or not it’s going to make economic sense. There is still plenty of grid technology development that needs to happen to get to the level of resilience and supply that we want to enjoy.”

In-space SBSP hardware demonstrations are justified and sensible, Jaffe says, before any commitment to developing full-blown systems. Such testing, he notes, is likely to cost hundreds of millions of dollars, and even with such start-up funding secured, SBSP would still require sustained political support. Whether it ever takes off depends just as much (if not more) on economics and regulatory factors as on technological development.

“At the end of the day, it boils down to doing this in a way that is cost-competitive with the alternatives,” Jaffe says.

John Mankins, a former NASA technologist and longtime SBSP activist, remains bullish on the approach’s prospects. Fittingly, he is also current co-chair of the International Academy of Astronautics’ Permanent Committee on Space Solar Power.

In the past, SBSP plans have been hamstrung by three interlinked financial obstacles: the high costs of building the necessary hardware, ensuring that hardware is suitable for the space environment and then actually placing it in orbit. “All three of those have been shattered,” Mankins says, by advances in space robotics, the ability to mass produce SBSP components and the plummeting price tag of hurling hardware into space.

Taken together, he says, this triple-header of positive trends could slash the up-front investment costs by hundreds of billions of dollars, tipping SBSP into a new era of economic feasibility. That, Mankins says, is more than enough motivation to spark today’s multinational interest and engagement in SBSP.

GLOOMY FORECASTS

Not everyone holds such sunny views of SBSP’s prospects. One notable critic is Amory Lovins, an expert on energy policy and co-founder and chairman emeritus of RMI (formerly Rocky Mountain Institute), a nonprofit that seeks to improve the world’s energy practices. He is an adjunct professor of civil and environmental engineering at Stanford University and a scholar at the university’s Precourt Institute for Energy.

Lovins says that launch costs “remains a formidable obstacle” to SBSP despite the roughly 20-fold drop in the per-kilogram cost of lofting payloads to low-Earth orbit (when comparing the cost-performance curve of NASA’s space shuttle with that offered by SpaceX’s Falcon booster family).

There are security concerns, too, Lovins says, recalling questions that still linger from the first spike in SBSP enthusiasm in the late 1960s. “Some folks back then wondered if microwave-beam-from-space weapons were part of the agenda,” he says. “Now we may be more concerned about adding yet another supercentralized power source to an already very vulnerable and brittle transmission grid.”

Although SBSP remains conceptually appealing, Lovins says other trends in renewable energy pose great challenges to its viability. Ground-based renewables have rapidly become radically cheaper, with wind and solar alike offering wholesale rates of three cents or less per kilowatt-hour of power. And integrating these “terrestrial” sources to preexisting grids in ways that ensure “firm” power delivery adds little cost, he says. This leads Lovins to conclude that the much-touted benefit of SBSP—its effectively constant availability irrespective of earthly days and nights—is of only small benefit. Under such circumstances, he says, going to space to beat the bargain-basement cost per kilowatt-hour of terrestrial renewables remains extremely hard, if not impossible.

“In brief, I think a photovoltaic cell will deliver cheaper power from your roof—probably even in Seattle—than from space,” Lovins says. “I’m not a space expert, but it’s not obvious to me that this basic handicap of SBSP will change. Terrestrial wind and [the] photovoltaic cell are both set to drop another two to three times in cost, making their energy very close to free.”

Why go to so much trouble and expense gathering sunlight beyond Earth’s atmosphere, Lovins asks, “when it’s already distributed for free, falling, like rain, on the just and the unjust alike?”

Like SBSP itself, finding a definitive answer for that philosophical question remains a work in progress.

Via ScientificAmerican.com

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