Space-Based Power: Intermediate Relays Could Help - IEEE Spectrum

Nov 08, 2024

This article is part of our exclusive IEEE Journal Watch series in partnership with IEEE Xplore.

As part of the ongoing search for more sustainable energy solutions, some researchers are thinking outside the box—or globe, really. One team in California is proposing a new transmitter array system that could help harvest energy directly from space. Through prototype tests on smaller, Earthly scales, they demonstrate how their proposed system can more than double the amount of power transferred between power harvesters and receivers, or extend their range by a similar factor.

The concept of harvesting energy from a space-borne solar array and beaming it to Earth’s surface was first proposed in the 1940s, as science fiction. But the idea has sparked interest among scientists, prompting them the explore its real-world feasibility. Whereas wind and solar energy harvested on Earth is dependent on weather conditions, harvesting energy directly from space would theoretically provide a more consistent supply of energy.

But the approach comes with some obvious challenges, including successfully directing and refocusing the power beam—microwave frequencies, in this case—in the desired direction. Across such vast distances, very large transmitters in space and receivers on Earth would be necessary to pick up the power signals, which would inevitably disperse over such long transmission distances.

To address this issue, Ali Hajimiri, a professor at the California Institute of Technology, and his colleagues are exploring the possibility of an intermediate system of programmable transmit array that orbits Earth at an altitude between the space-based transmitters and the Earth-based receivers. Such an “relay” approach would give scientists more control over where the beam is directed on Earth’s surface, and ensuring more power successfully finds its target. Alternatively, it would allow for smaller transmitters and receivers.

”Programmable transmit arrays placed in some intermediate orbit can alleviate this size requirement greatly by refocusing the beam, allowing for use of smaller transmitter and receiver systems,” says Hajimiri.

The proposed transmitarray would work as an intermediate step to more effectively beam power from space to Earth.Ali Hajimiri et al.

The researchers describe their proposed transmitter array system in a study published 2 October in the IEEE Journal of Microwaves. The system is a constellation of equally-spaced transmitarray antennas occupying the same orbit. As one transmitarray moves away from the main solar harvesting array system in space (called the active array), a second transmitarray would approach and take over relaying the power to Earth as the first one moves out of range.

In their study, the researchers designed and tested several low-cost, light-weight proof of concept transmit arrays to refocus the beam, finding the tactic could transfer nearly 2.5 times as much power as a system that would beam power straight to Earth. The experiment involved a small proof-of-concept prototype with the power transmitter and receiver 3.8 meter apart in an anechoic chamber. The power boost means the systems could work across greater distances, or require smaller transmitter and receivers for a given distance.

Hajimiri notes that, while the implementation of this intermediate array would increase the overall cost of the system, the increased energy yield would make the system more cost-efficient—per unit of energy—over its lifespan.

While a fully functional space-to-Earth power transmitter is still far in the future, Hajimiri and his colleagues plan to continue to develop and test their solutions. “One of [our] areas of focus is building larger-scale and more programable transmitarrays and test them in a space environment,” Hajimiri says.