Caltech scientists powered up on results of mission to harness energy from space
At Caltech, a milestone has been reached in the search for a new, clean energy source for Earth’s growing electricity demands, fueling researchers’ optimism that harnessing power from space is achievable.
But it took a daring rescue and some quick-thinking solutions.
On Nov. 11, 2023, Caltech’s Space Solar Power Project concluded a series of experiments that had been launched into Earth’s orbit 10 months earlier. This week, officials offered an assessment on the concluded mission.
The project’s team is designing satellites, which may someday orbit our planet, collecting energy from the Sun and beaming it back to Earth, where it can be converted into electricity. It’s an approach called “space solar power.”
The experiments – which sat atop a small, platform-like spacecraft – were testing the team’s designs for the key technologies that will make these satellites possible.
Caltech President Thomas F. Rosenbaum was optimistic about the future for space solar power.
“Solar power beamed from space at commercial rates, lighting the globe, is still a future prospect. But this critical mission demonstrated that it should be an achievable future.”
The team is now celebrating the mission’s successes and poring over their findings in order to inform the project’s future directions.
A pioneering prototype
The mission consisted of three sets of experiments testing the three technologies that are core to the team’s design: lightweight space structures; solar energy collection; and wireless power transfer.
The Deployable on-Orbit ultraLight Composite Experiment – known as DOLCE – tested the team’s design for a lightweight structure that could someday form the skeleton of the space solar power satellites. Dr. Sergio Pellegrino, one of the project’s three primary investigators, leads the team that built, deployed and monitored the 1.8-meter-by-1.8-meter, picture-frame-shaped prototype.
The mission was meant to demonstrate not only how well the three technologies performed, but also what might go wrong.
According to Caltech, at the beginning of the DOLCE experiment, when it was meant to begin its three- or four-day unfolding sequence, the structure hit a snag, becoming tangled in a wire which caused some damage. In a scene right out of Ron Howard’s “Apollo 13”, Pellegrino’s team had to troubleshoot the issue using a model of DOLCE in their lab at Caltech.
Discovering that the structure would unfold better under the Sun’s warming rays, the team devised a solution, rescuing DOLCE.
Prior to the zero-gravity mission, the structure had only been observed under Earth’s gravity. The experiment was an opportunity for Pellegrino’s team to discover challenges unique to space.
“The troubleshooting process has given us many new insights…We have developed new ways to counter the effects of self-weight in ultralight deployable structures,” Pellegrino said.
The cells
Alba, which translates to “dawn” in Italian, is another experiment upon the spacecraft, which tested 32 types of photovoltaic cells, which transform solar energy into electrical energy.
Dr. Harry Atwater, chair of the Division of Engineering and Applied Science and one of the SSPP primary investigators, leads the team that developed these cells. His team continues to analyze how well they performed and withstood the harsh environment in space, where they faced solar radiation and geomagnetic forces among other woes.
The mission was entirely funded through private sources and operated entirely by private organizations. Some of the cells were manufactured directly at Caltech.
“SSPP gave us a unique opportunity to take solar cells directly from the lab at Caltech into orbit, accelerating the in-space testing that would normally have taken years to be done,” Atwater explained. “This kind of approach has dramatically shortened the innovation-cycle time for space solar technology.”
Energy beams
The third experiment deployed into orbit was the Microwave Array for Power-transfer Low-orbit Experiment – MAPLE.
MAPLE carried an array of microwave transmitters capable of switching on and off within nanoseconds, allowing the researchers to control the direction of concentrated energy beams. Dr. Ali Hajimiri, Bren Professor of Electrical Engineering and Medical Engineering and a primary investigator on the project, led the team responsible for MAPLE.
In June, 2023, Hajimiri’s team demonstrated their ability to successfully beam energy directly at targets in space and on the Earth. After this successful demonstration, Hajimiri’s team observed MAPLE’s beam losing power as time went on. Using this data, the team tracked down the causes behind the weakening beam.
“These observations have already led to revisions in the design of various elements of MAPLE to maximize its performance over extended periods of time,” Hajimiri explained.
The Future
With the mission concluded, the SSPP team will refine their designs for economically feasible space solar power.
“It’s not that we don’t have solar panels in space already. Solar panels are used to power the International Space Station, for example,” Atwater explained. “But to launch and deploy large enough arrays to provide meaningful power to Earth, SSPP has to design and create solar power energy transfer systems that are ultra-lightweight, cheap, flexible, and deployable.”
The SSPP team will be refining their approach to fueling the planet with solar power from space.
Project Origins
The SSPP project began in the 2011 when Donald Bren, chairman of the Irvine Company, and his wife, Brigette Bren, a trustee at Caltech, committed $100 million to fund the research.
Bren had been interested in space solar power ever since reading a Popular Science article describing the technology’s potential in his younger years. Northrup Grunman Corporation later chipped in $12.5 million as part of a research agreement with Caltech.
Eventually both the spacecraft and experiment will submit to Earth’s gravity, burning up into a mixture of smoke and gases as it re-enters the atmosphere. And even then, scientists will continue their goal of power from space.
