An orbital satellite testing the technological feasibility of one day harvesting and transmitting solar energy down to Earth has concluded its year long mission, and researchers are eager to dive into the results. According to Caltech’s mission recap released today, engineers behind the Solar Space Power Demonstrator (SSPD-1) consider all three of 110-pound prototype’s onboard tools a success and believe the project “will help chart the future of space solar power.” That future, however, is still potentially decades away, if such projects are funded.
Launched aboard a SpaceX Falcon 9 rocket in early January 2023, the SSPD-1 contained a trio of experiments: First, its Deployable on-Orbit ultraLight Composite Experiment (DOLCE) investigated the durability and efficacy lightweight, origami-inspired solar panel structures, while ALBA (Italian for “dawn”) tested 32 different photovoltaic cell designs to determine which may best be suited for space. At the same time, the Microwave Array for Power-transfer Low-orbit Experiment (MAPLE) tested microwave transmitters meant to convey solar power harvested in orbit back to Earth.
[Related: A potentially revolutionary solar harvester just left the planet.]
Perhaps most importantly, MAPLE successfully demonstrated for the first time ever that solar power can be collected by photovoltaic cells and transmitted down to Earth via a microwave beam. Over the course of eight more months, SSPD-1 team members purposefully ramped up MAPLE’s stress tests, eventually leading to a drop in transmission capabilities. Researchers then reproduced the issue in a laboratory setting, eventually determining that complex electrical-thermal interactions and the wear-down of individual array components were to blame.
Ali Hajimiri, co-director of Caltech’s Space Solar Power Project (SSPP) and the Bren Professor of Electrical Engineering and Medical Engineering, announced today that the results “have already led to revisions in the design of various elements of MAPLE to maximize its performance over extended periods of time.”
“Testing in space with SSPD-1 has given us more visibility into our blind spots and more confidence in our abilities,” Hajimiri added.
Today’s solar cells used in satellites and other space technologies are as much as 100 times more expensive to manufacture than their terrestrial counterparts. Caltech explains this is largely due to the cost of adding protective crystal films known as epitaxial growth. ALMA determined that perovskite solar cells, although a promising design here on Earth, showed major performance variabilities in space. At the same time, gallium arsenide cells worked consistently well over a large period of time—but without the need for including epitaxial growth.
As for DOLCE, researchers readily admitted on Monday that “not everything went according to plan.” Although originally meant to deploy over three-to-four-days, DOLCE encountered multiple engineering issues, such as snagged wiring and jammed mechanical components. Thankfully, the team managed to sort out the issues by referencing onboard cameras to mimic the problems on a full-scale lab replica. Despite the headaches, DOLCE’s space test “demonstrated the robustness of the basic concept,” according to SSPP co-director and Joyce and Kent Kresa Professor of Aerospace and Civil Engineering, Sergio Pellegrino.
[Related: Are solar panels headed for space?]
But even with SSPD-1’s overall successes, it still may be years before solar power could be efficiently and affordably amassed using satellite arrays. Previous estimates put solar power gathered in space at costing $1-2/kWh, while it is currently less than $0.17/kWh for US electricity. Material costs will need to drastically decrease, while also still remaining strong enough to endure space’s solar radiation and geomagnetic activity.
There are other issues that need addressing before space-derived solar power can ever contribute to humanity’s sustainable energy infrastructure. As The New York Times noted last year, the amount of energy transferred by SSPD-1 through a microwave beam was extremely negligible compared to what’s needed for everyday use, and such orbital solar arrays will likely need to be several thousand feet wide—the International Space Station, for reference, is just 357-feet-long. There are also questions of safety regarding beaming powerful microwaves and laser beams back to Earth.
SSPP researchers are aware that all these problems require solutions before orbital solar farms are truly possible. But their most recent progress indicates that, at the very least, they appear to be on a promising path.