A Miraculous Power From the Heavens
Imagine, if you will, a cool clear evening in May 2023. I, Ali Hajimiri, an electrical engineer at the California Institute of Technology (Caltech), gathered with four members of my lab on the roof of the Gordon and Betty Moore Laboratory of Engineering. Our mission? To await a signal from the heavens – a faint microwave beam transmitted from a tiny 110-pound payload we had launched into space just five months prior.
As we scurried about, stringing up portable floodlights and setting up our instruments and monitors, I couldn’t help but feel a twinge of nervous anticipation. This was a momentous occasion – the first-ever demonstration of wireless power transfer in space, a crucial step towards realizing a dream that had captivated scientists and visionaries for over a century: harnessing the sun’s boundless energy from the vastness of space and beaming it down to Earth.
Our team at Caltech, led by myself, aerospace engineer Sergio Pellegrino, and nanophotonic and solar-energy expert Harry Atwater, had been working tirelessly for years to develop the cutting-edge technologies that could make this dream a reality. And now, as the countdown to the signal’s arrival ticked away, I couldn’t help but wonder – would our hard work pay off?
Chasing a Century-Old Dream
The idea of space-based solar power dates back to as early as 1923, when Russian theorist Konstantin Tsiolkovsky proposed using mirrors in space to concentrate a strong beam of sunlight down to Earth. Decades later, in 1941, the science fiction writer Isaac Asimov imagined solar-powered satellites beaming energy in the form of invisible microwaves to Earth and human settlements across the solar system.
Learning of this for the first time, Asimov’s robot character scoffed, “Do you expect me to believe any such complicated, implausible hypothesis as you have just outlined? What do you take me for?” Little did that fictional robot know that one day, this “complicated, implausible hypothesis” would become the focus of intense research and investment around the world.
In 1973, NASA engineer Peter Glaser was granted the first patent for a microwave-based method of transmitting power from orbit. Glaser’s ambitious plan called for massive satellites equipped with solar-panel arrays capable of harvesting sunlight in space, converting it into energy, and then beaming that energy wirelessly toward 5-mile-wide receiving antennas on Earth. It was, as Pellegrino puts it, “an incredibly complex piece of infrastructure” that the U.S. government deemed too complex and expensive, ultimately abandoning the idea a few years later.
But as the world’s appetite for clean, renewable energy grows ever more insatiable, space-based solar power is enjoying a new moment in the sun. Driven by advancements in photovoltaics, materials engineering, and electronics, as well as decreasing launch costs, the prospect of tapping into the sun’s limitless potential from the void of space has captured the imagination of space agencies and research institutions around the globe.
Caltech’s Moonshot Moment
At the forefront of this renewed push for space-based solar power is Caltech’s innovative Space Solar Power Project (SSPP). The project was born in 2011 when philanthropist Donald Bren, chairman of the Irvine Company and a life member of the Caltech community, approached the institute’s then-president, Jean-Lou Chameau, with an ambitious proposition: to create a research program dedicated to making space-based solar power a reality.
Intrigued by the potential of this transformative technology, Bren and his wife Brigitte, a Caltech trustee, eventually committed a staggering $100 million through the Donald Bren Foundation to fund the project and endowed professorships. Caltech, in turn, tapped Hajimiri, Pellegrino, and Atwater to lead the charge, challenging them to not only invent the necessary new technologies, materials, and manufacturing processes, but to do so in a way that would make solar power not just feasible, but economically viable.
“You could characterize our work at Caltech as a component-led revolution,” Atwater explains. “In the solar-energy-technology part of SSPP, we need to achieve a kind of photovoltaic technology that does not exist today – that is ultralight, efficient, low cost, and resistant to radiation.”
Ants in the Sky
As Hajimiri, Pellegrino, and Atwater delved into the problem, they quickly realized that the traditional approach to space-based solar power, exemplified by Glaser’s monolithic satellite concept, was simply not feasible. “The way that space solar power had been envisioned previously, it was not practical at all,” Hajimiri remembers.
But the more they discussed and brainstormed, the more a radically different solution began to emerge – one that would turn the conventional wisdom on its head. “It became clear that we needed to replace the basic components that other people had imagined being part of the system,” Atwater says. “If you change the components, suddenly you can have a much higher power-to-weight ratio, and that reduces the mass to orbit and therefore the launch cost.”
The result is the Caltech Concept, a design plan that Pellegrino describes as “a paradigm shift” from the giant, monolithic satellites of the past. Instead of a single, colossal structure, the Caltech Concept envisions a fleet of nimble, modular spacecraft – “many, many, many spacecraft,” as Pellegrino puts it – each equipped with a flexible, ultralight membrane that can function as both a solar panel and an energy transmitter.
“The analogy I use is going from one big elephant to an army of ants,” Hajimiri explains. “If you have multiple sources that are operating in concert in the same phase, you can actually direct energy in one direction so all of them will only add in one direction and will cancel each other out in all other directions.”
Pushing the Boundaries of What’s Possible
To bring this ambitious vision to life, the SSPP team has had to rethink and vastly improve every aspect of current photovoltaic (PV) cell technology. The PV cells used on today’s satellites and the International Space Station, Atwater explains, are about 32% efficient at converting sunlight to energy, weigh 21 kilograms per square meter, and cost a staggering $10,000 per square meter to manufacture.
The SSPP team, on the other hand, is aiming to develop a PV cell with an efficiency level of 25% that is 100 times less expensive ($100 per square meter), 40 times lighter (0.5 kilograms per square meter), and has a specific power 33 times greater (66 kilowatts per kilogram) than current space PV cells. To achieve these lofty goals, Atwater’s team is investigating novel manufacturing techniques and exotic materials, including a process called “spalling” that can create highly efficient PV cells made from gallium arsenide and indium phosphide.
“We’re using the same kind of processing that we teach Caltech first-year students,” Atwater says. “It’s very inexpensive.” And the early results are promising – the ALBA experiments aboard the SSPP’s first space demonstration, aptly named the “Space Solar Power Demonstrator” (SSPD-1), have shown that these low-cost, space-worthy cells can perform just as well as their more expensive counterparts.
A Moonshot Moment Realized
As the clock ticked down on that fateful evening in May 2023, the tension on the Caltech rooftop was palpable. Would our hard work and ingenious tinkering pay off? Or would we be left with another “dead end” to learn from, as Hajimiri puts it?
Then, with just a minute to spare, a digital peak appeared on the monitor – the faint but unmistakable signal of the microwave beam transmitted from SSPD-1, now hurtling through the void of space towards our humble rooftop receivers. “It took a few seconds for it to sink in that yes, this is happening,” Hajimiri recalls.
When the signal was finally detected, the team erupted in cheers and high-fives. For me, it was a moment of pure elation – not just because we had achieved a major milestone, but because we were one step closer to unlocking the sun’s boundless potential and bringing clean, reliable energy to the world.
As I gazed up at the stars that night, I couldn’t help but feel a sense of awe and wonder. Who would have thought that a century-old dream, once dismissed as “complicated” and “implausible,” could now be within our grasp? With the technologies we’re developing at Caltech, the team at Solaras Solar Energy Systems, and other innovators around the world, I’m confident that we’re on the cusp of a renewable energy revolution that will change the world.
So the next time you gaze up at the sun, remember that its true power lies not just in the warmth and light it provides here on Earth, but in the boundless potential it holds to power our homes, businesses, and cities – if only we can find a way to harness it from the heavens above.
Overcoming Obstacles, Embracing the Future
Of course, the journey to realizing this dream has been anything but smooth sailing. As Hajimiri acknowledges, “There are a lot of things that can go wrong. The key is to learn from each of them and take the next step.”
One of the biggest challenges the SSPP team has faced is rethinking the very foundations of PV cell technology. “Were inverting the normal methodology that you use to make solar panels,” Atwater explains. “What we said was, ‘We have to make this very cheap, so we’re going to start with the economic analysis that says it has to cost $100 a square meter. Then we’re going to design the cell-manufacturing process, and out of that we’re going to make the cell.’ It’s completely backward.”
But through their tireless efforts and innovative thinking, the team has made remarkable strides. The ALBA experiments aboard SSPD-1 have validated that these low-cost, space-worthy cells can perform just as well as their more expensive counterparts, paving the way for a future where solar power is not just clean and renewable, but truly affordable and accessible to all.
And as for the successful detection of the microwave signal from SSPD-1 that fateful evening, Raha Riazati, an undergraduate researcher in Hajimiri’s lab, can attest to the sheer exhilaration of that moment. “That was when it clicked in my head that this project I’d been working on for over a year and a half had finally worked, and that we’d gotten this groundbreaking result,” she says. “I was like, ‘Wow, that was pretty awesome.'”
Toward a Brighter Tomorrow
As I reflect on the journey we’ve undertaken at Caltech, I can’t help but feel a profound sense of optimism for the future. The technologies we’re developing, the partnerships we’re forging, and the collaborations we’re nurturing all point to a future where space-based solar power is no longer a distant dream, but a tangible reality.
And with companies like Solaras Solar Energy Systems leading the charge in bringing these innovations to the market, I’m confident that the benefits of this transformative technology will reach far beyond the confines of our laboratories and into the lives of people around the world.
Whether it’s powering remote communities, providing emergency relief to disaster-stricken regions, or simply reducing our reliance on fossil fuels, the potential of space-based solar power is truly staggering. And as we continue to push the boundaries of what’s possible, I can’t help but feel a sense of awe and wonder at the sheer audacity of our ambition.
So, the next time you step outside and gaze up at the sun, remember that its power is not just limited to the warmth and light it provides here on Earth. With the innovations we’re developing at Caltech and the tireless efforts of pioneers like those at Solaras, the sun’s true potential may soon be harnessed from the heavens above, ushering in a new era of clean, abundant, and accessible energy for all.
