Stationary solar panels aren’t the only way we can harvest the raw power of the Sun. In a groundbreaking experiment conducted last year, researchers across the public and private sectors successfully collected solar power using an orbiting satellite and then beamed that energy down to Earth. The team has since detailed the results of their experiment in a new paper shared to the arXiv.
The team behind the achievement is the California Institute of Technology’s (Caltech) Space Solar Power Project, or SSPP. In collaboration with Indie Semiconductor, Inc., NASA's Jet Propulsion Laboratory (JPL), Amazon Web services, and a Caltech spinoff startup called GuRu Wireless, the SSPP developed a prototype last year called the Space Solar Power Demonstrator (SSPD-1). This prototype will eventually be responsible for three experimental technologies, one of them being space solar power.
We already use sunlight and solar panels to generate electricity here on Earth, but even our most advanced methods have their shortcomings. A cloudy, rainy day can cause a solar panel’s output to drop up to 25%, and for obvious reasons, stationary panels can’t generate electricity at night. But orbiting solar panels can work at night, as long as they orbit in a way that keeps them in contact with the Sun’s rays. Scientists just have to figure out a way to reliably beam the energy they gather down to Earth, where it can be used to power homes, businesses, public resources, and more.
That’s the idea behind MAPLE, the Microwave Array for Power-transfer Low-orbit Experiment that makes up one of SSPD-1’s three key technologies. Built around a 6U CubeSat chassis, MAPLE takes the solar power collected by SSPD-1’s solar cells and converts it into radio frequency (RF) power using its rectifying antenna arrays. Then a pair of custom 16-channel silicon radio frequency integrated circuits (RFICs) synthesize a beam of RF power that can be transmitted down to Earth. On the roof of Caltech’s Moore Laboratory, a tracking apparatus keeps an “eye” on MAPLE’s location, while an RF receiver accepts incoming energy and converts it to direct current (DC) energy.
On Jan. 3, 2023, the SSPP launched SPPD-1 into low Earth orbit (LEO) using a SpaceX Falcon 9 rocket. Exactly two months later, the SSPP started experimenting with using MAPLE to beam energy down to Caltech. Though the SSPP’s preprint paper—which is currently awaiting peer review—says there was a touch of power degradation toward the end of each attempt, the experiment was successful throughout its 10-month duration.
Eventually, the SSPP hopes to create a constellation of SPPD-1-type satellites that can transmit enough power to supply 10,000 homes. There’s no denying they have a long way to go: Though MAPLE was able to capture anywhere from 175mW to 251mW at a time in space, only 1mW made it down to Caltech’s ground station. Still, the SSPP’s experiment isn’t meant to supplement our power grid anytime soon, but rather to prove the feasibility of capturing solar power in space.
