The hottest day in world history is as good a reason as any to think about getting fossil fuels out of our energy mix.
The space-based answer to the problem is straightforward, at least on its face: Let’s put solar panels out there and beam the electricity they generate back down to Earth. The idea populated Isaac Asimov’s science fiction as early as 1941; the first serious scientific proposal dates to 1968.
The attraction is simple: Photovoltaic cells can generate more power without the interference of the atmosphere. And in the correct orbit above the Earth, they can do so nearly 24 hours a day, eliminating the timing issues that plague terrestrial renewable energy.
The obstacles are equally simple: Getting a large enough solar-power satellite into space is simply too expensive. A US Department of Energy study of the idea in 1979, motivated by the oil crisis, estimated the cost of space solar power at $495 billion in today’s dollars. That’s more than the $302 billion current-dollar cost of the entire Apollo moon program.
Today, electronics are becoming lighter and more capable, as rockets become cheaper and more powerful. With the added motivation of fighting climate change, does the economic case now close for space solar power?
Maybe! Cost is still a driver. In 2000, NASA thought these plans would pencil out if launch costs fell to between $100 and $200 per kilogram; today, SpaceX is offering prices around $3,000 per kg to commercial customers. If the company’s next rocket, the enormous and reusable Starship, gets into orbit and faces more competition, that ultra-low launch cost might be realized.
But there’s also a lot to be done to make space solar power satellites cheaper and lighter. Ali Hajimiri is a professor at the California Institute of Technology and an expert in radio-frequency chips that, among other things, helped make modern mobile phones possible. Now his focus is on wireless energy transfer, an invention he expects will be as ubiquitous and world-changing as wifi. His laboratory benefits from $100 million donation from philanthropist Donald Bren specifically to take space solar power “from the pure realm of science fiction to something that has practical application.”
In March, Hajimiri and his team put their first spacecraft through its paces, demonstrating the ability to transmit solar power wirelessly in space. (Despite some headlines, the device did not transmit any power back to Earth.)
“The challenge with wireless energy transfer in general,” Hajimiri tells me, is that “it is such a different kind of technology that there is no framework existing for thinking about it.” I had to ask: Could someone be zapped by energy transmitted down from space? His answer is no, not in a well-designed system which relies on low energy density that doesn’t cause chemical changes. A good analogy is sunlight itself, which can generate electricity without harming humans (at least in the near-term).
Hajimiri’s team is focused on using phased array technology. Reductively, these are many small antennas combined into a single device that can manipulate and focus energy precisely through software instruction, rather than relying on the physical shape of an antenna or its motion to steer radio energy. Originally invented for military radars, phased array antennas are used in 5G phones and by Starlink communications satellites.
The goal is to create a single, flexible sheet that integrates solar cells on one side and phased array transmitters on the other. Lightweight and foldable to fit into a rocket fairing, it would expand in space to ultimately become a satellite about a kilometer in area. Such a spacecraft would feed a power receiving station on Earth of roughly the same size, and generate about 100 MW of electricity. For comparison, Solar Star, an enormous windfarm in southern California, generates about 579 MW on 13 km².
The biggest difficulty, Hajimiri says, is ensuring that this huge array of antennas are acting in concert, within picoseconds of one another—that’s one-trillionth of a second. He’s also focused on ensuring his architecture is economically sustainable, citing his experience in the chip-making industry as a guide. He doesn’t yet have a cost estimate to share for the total system, but one recent paper forecasts that a phased array sheet suitable for his power station might be mass produced at a cost of less than $100,000.
Besides the CalTech team, other organizations working on space solar power include the US Air Force, the European Space Agency, Japan’s space agency, and the China Academy of Space Technology.
If such a system can get off the ground—it might take 10 years, with “big caveats” per Hajimiri—this technology could have major impact, not just supplementing the existing grid but delivering energy on demand to places where the grid has been damaged by natural disaster or war. He also imagines places without transmission networks leapfrogging directly to space solar power, just as some developing nations adopted mobile phones before landlines could be installed.
“One of the challenges we are facing right now is incrementalism,” Hajimiri says. “There’s a lot of incremental [work] that’s important and essential, [but] it should not come at the cost of potentially large risk, but large reward, projects.”
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IMAGERY INTERLUDE
The first solar-powered satellite was the US Vanguard-1, which launched in 1958 and is still up there.
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SPACE DEBRIS
SpaceX and FAA move to throw out Starship lawsuit. After the failed first attempt to put Starship in orbit, a coalition of community groups sued the FAA, arguing it should not have granted SpaceX a launch license. Now, the agency and SpaceX have filed to dismiss the suit, with the FAA arguing that the groups don’t have standing to challenge its regulatory decision.
The final flight of the Ariane 5. Arianespace’s flagship rocket went to orbit for the last time yesterday, which will leave Europe reliant on the US for most rocket launches for at least a year. Also: What is the future of Europe’s South American spaceport?
Virgin Galactic flies three more astronauts. The space tourism company’s first revenue-generating flight went off without an apparent hitch on June 29, but its business is back to square one: building a new rocket plane that can fly often enough to earn a profit.
The US military still wants rocket transportation. A new program from the Defense Innovation Unit is asking companies to send in proposals to autonomously move cargo to space, through space, and back to Earth. Given the failure of any companies to win DIU’s responsive launch contest, this project may still be a little too innovative.
North Korea’s satellite wasn’t any good. The spacecraft, which failed to reach orbit, was recovered by South Korea and assessed to have little military value. That’s what they would say, but it does jibe with the reality that launch vehicles are easier to construct than spy satellites.
Last week: What will it take to get Starship and other debut rockets off the ground?
Last year: It’s Elon Musk versus Charlie Ergen in a battle for the airwaves.
This was issue 187 of our newsletter. Hope your week is out of this world! Please send your most fanciful vision of space solar power, tips, and informed opinions to tim@qz.com.