A multidisciplinary team from the California Institute of Technology is a winner of the 2024 Gizmodo Science Fair for testing a satellite that proves it’s possible to collect solar energy in space and then send it down to Earth as usable power.
Long a staple of science fiction authors and futurists, the idea of harnessing solar power directly from space has been thwarted by technological and cost barriers. The promise is tantalizing: a vast, uninterrupted supply of clean solar energy, unaffected by day-night cycles, seasons, or weather, and potentially offering more power than Earth-based solar panels. Encouragingly, recent experimental results point to the feasibility of the concept—an innovation with the potential to dramatically transform how we capture and distribute energy to Earth.
The question
Is it possible to efficiently and affordably harvest solar power in orbit, transmit it through space, and then down to Earth? Can space-based solar power provide a continuous and more reliable energy source than ground-based solar panels, and could space-based solar power help overcome the limitations of terrestrial solar energy, such as weather, nighttime, and land use?
The results
Caltech’s Space Solar Power Demonstrator-1 (SSPD-1) was a milestone advancement in the development of space-based solar power. Though modest in scope, this proof-of-concept experiment could lead to bigger things. Like, enormously bigger things.
SSPD-1 launched to space in January 2023 aboard a Falcon 9 rocket, integrated within Momentus’ Vigoride-5 spacecraft. Its mission was to collect solar power in orbit and transmit it both in space and back to Earth. It also tested deployment mechanisms and innovative new solar technologies. Ultimately, SSPD-1 served as a feasibility experiment: Can it gather solar power in space and beam it, in the form of microwaves, down to Earth as useful energy?
The project had three main ingredients: DOLCE (for deploying the structure), ALBA (for harvesting solar energy), and MAPLE (for wireless power transmission). These three elements were considered the basic requirements for moving forward with a larger-scale project.
The DOLCE (Deployable on-Orbit ultraLight Composite Experiment) featured a 6-by-6-foot structure that unfurled shortly after launch, demonstrating a fundamental requirement for constructing large-scale solar arrays for power collection in space. DOLCE showed that “you can have something that wraps, unwraps, and deploys in space in simple fashion,” said Ali Hajimiri, an electrical engineer at the California Institute of Technology and one of three PIs on the SSPD-1 development team.
The ALBA component tested the efficiency of different photovoltaic cells in space. This experiment involved 32 types of cells, some of which had never been used in space. ALBA’s crucial finding was identifying the most effective solar cells for space applications. This data will likely prove vital for optimizing solar power generation in future projects.
- MAPLE (Microwave Array for Power-transfer Low-orbit Experiment) demonstrated the feasibility of wireless energy transmission in space, whether in orbit or to receiving stations on the ground. This experiment involved a flexible array of microwave power transmitters, showing the potential of using cost-effective silicon technologies in space. MAPLE showed it’s possible to transfer energy in the vacuum of space—an essential step toward realizing space-based solar power.
Why they did it
Space-based solar power has been around as a concept for a long time, with legendary sci-fi author Isaac Asimov introducing the idea in his 1941 short story “Reason.” Experts ruminated over the possibility for decades, but it remained stuck within the confines of science fiction. But the appeal of space-based solar never faded.
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The interior of MAPLE, showing the transmission array at right and the receivers on the left. Image: SSPP
Early concepts required massive, heavy structures and extensive in-space manufacturing, which was impractical with launch capacities both then and now. The cost of fabricating these large structures would be prohibitively high compared to the energy return they would generate, explained Harry Atwater, a project PI and Caltech materials engineer.
Solar panels already power the International Space Station, but for the Space Solar Power Project (SSPP) to deliver energy to Earth, the researchers needed to develop solar energy transfer systems that were small, ultra-lightweight, cost-effective, and flexible for launch and deployment. Experts considered the demonstration of wireless power transfer in space using lightweight structures a crucial step toward advancing space-based solar power for global use.
The Caltech team aims to “realize the vision of space solar power in a scalable and economic fashion,” said Atwater, and to “disrupt the component level of the technology by creating ultra-light, low cost, and flexible components.”
Why they’re a winner
The breakthroughs offered by DOLCE, ALBA, and MAPLE represent a leap forward in this field. The team overcame several challenges during the mission, including glitches during the deployment phase, which weren’t easy to resolve given the challenges of working in space.
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The team detecting power from MAPLE on the roof of Moore Laboratory. Photo: Caltech/SSPP
“It was not a pleasure cruise in terms of being able to communicate with the spacecraft and getting the data downloaded,” Hajimiri said. “It took a few months for some of these things to be worked out. We had, even until the end, issues with several different aspects of it. But the major part of the mission was successful because we could find workarounds.” He added: “If you don’t have any challenges, problems, or minor failures, you don’t learn as much.”
The work done to advance solar cell technology, and the successful demonstration of wireless power transmission in space, lays the foundation for future improvements in the concept. The energy beamed down to Earth was a token amount, “but it was enough to just say, ‘hey, this is working,’” said Atwater.
And there’s the humanitarian and environmental aspect to consider. Space-based solar power promises an unlimited, clean energy source that could significantly reduce our reliance on fossil fuels.
The proposed system is also safe. It’s designed with inherent limitations set by natural physics, ensuring that the energy transmitted never exceeds a certain threshold. Accordingly, the system shouldn’t overheat equipment, interfere with electronics, or cause harm to living organisms. It also employs low-powered microwaves for energy transfer, which are primarily heat-generating and considerably safer than solar radiation, according to the researchers. The concern has to do with humans, animals, and electronic devices that could be affected by high-intensity radiation; but the low-powered microwaves aren’t likely to pose any harm. Moreover, the system is equipped with intelligent controls that can adapt to unforeseen circumstances, such as obstacles in the energy path.
What’s next
The team is currently reviewing the mission’s outcomes, gathering data and insights that could inform a second mission to further refine the concept.
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A prototype antenna sheet for the power transmitter, displaying its flexibility. Photo: Caltech/SSPP
In the future, the Caltech group envisions launching a fleet of modular spacecraft designed to harness sunlight, convert it into electricity, and subsequently transform it into microwaves. This system, should it work as planned, would be capable of directing energy to specific locations on Earth using an array of power transmitters working in concert. The generated microwaves would be transmitted through the air over vast distances, providing power even to regions without stable access to electricity. Remarkably, the power from this system could be receivable without the need for specialized infrastructure on the ground (the system uses microwave receivers, which can be simple and lightweight, allowing them to be deployed quickly and easily), and could be used to deliver energy to remote areas or locations grappling with the aftermath of war or natural disasters.
In the future, large space solar power stations, potentially in geosynchronous orbit, could generate significant amounts of power, according to Atwater. For comparison, a typical Earth-based power station, like those using coal or nuclear energy, can produce between 500 megawatts and a gigawatt continuously. Space-based stations could serve various needs, offering 10 to 50 megawatts for remote or specialized applications, such as military bases or isolated communities. However, for integration into the power grid or supplying industrial customers, these stations would aim to provide at least a few hundred megawatts.
The team
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Left to right: Sergio Pellegrino, Harry Atwater, and Ali Hajimiri, the principal investigators of the Space Solar Power Project. Photo: Caltech/SSPP
The three principal investigators on the project are Caltech professors Harry Atwater and Ali Hajimiri, along with Sergio Pellegrino, an expert in aerospace engineering. The Space Solar Power Project brought together three multidisciplinary teams of aerospace engineers, physicists, and electrical engineers. The PIs “had to learn new things, but most of the work was done by the postdocs, researchers, graduate students, and even some undergraduate students,” Hajimiri said.
Click here to see all of the winners of the 2024 Gizmodo Science Fair.
