Once considered science fiction, technology capable of collecting solar power in space and beaming it to Earth to provide a global supply of clean and affordable energy is moving closer to reality. Through the Space-based Solar Power Project (SSPP), a team of Caltech researchers is working to deploy a constellation of modular spacecraft that collect sunlight, transform it into electricity, then wirelessly transmit that electricity wherever it is needed—including to places that currently have no access to reliable power.
“This is an extraordinary and unprecedented project,” says Harry Atwater, an SSPP researcher and Otis Booth Leadership Chair of Caltech’s Division of Engineering and Applied Science. “It exemplifies the boldness and ambition needed to address one of the most significant challenges of our time, providing clean and affordable energy to the world.”
The project is led jointly by Atwater, who is also the Howard Hughes Professor of Applied Physics and Materials Science, and two other researchers: Ali Hajimiri, Bren Professor of Electrical Engineering and co-director of SSPP; and Sergio Pellegrino, Joyce and Kent Kresa Professor of Aerospace and Civil Engineering, co-director of SSPP, and a senior research scientist at the Jet Propulsion Laboratory (JPL).
Harnessing solar power in space relies on breakthrough advances in three main areas:
- Atwater’s research group is designing ultralight high-efficiency photovoltaics (materials that convert light into electricity) that are optimized for space conditions and compatible with an integrated modular power conversion and transmission system.
- Hajimiri’s research team is developing the low-cost and lightweight technology needed to convert direct current power to radio frequency power (which is used to transmit cell phone signals, for example) and send it to Earth as microwaves. The process is safe, Hajimiri explains. Non-ionizing radiation at the surface is significantly less harmful than standing in the sun. In addition, the system could be quickly shut down in the event of damage or malfunction.
- Pellegrino’s group is inventing foldable, ultrathin, and ultralight space structures to support the photovoltaics as well as the components needed to convert, transmit, and steer radio frequency power to where it is needed.
The basic unit of the system the researchers envision is a 4-inch-by-4-inch tile that weighs less than a tenth of an ounce. Hundreds of thousands of these tiles would combine into a system of flying carpet-like satellites that, once unfurled, would create a sunlight-gathering surface that measures 3.5 square miles.
Work on the SSPP has been supported by more than $100 million in funding from Donald Bren, chairman of the Irvine Company and a life member of the Caltech community, and his wife, Brigitte Bren, a Caltech trustee. The Northrup Grumman Corporation provided funding for initial feasibility studies.
Atwater, Hajimiri, and Pellegrino discussed their progress—and the transformational potential of space-based solar power—as the project nears a significant milestone: a test launch of prototypes into space in December 2022.