A small step towards space solar energy, a success


California Institute of Technology scientists celebrate after a successful test flight of the technology needed to produce energy from space.

The mission, called Space solar energy demonstrator (SSPD-1), was a small-scale test of technologies that will be needed for future gigantic power plants in space. After its launch last January, SSPD-1 spent the last year evaluating different solar cells and deployment methods, and in March became the first technology to transmit energy wirelessly to Earth from space.

Although the mission was an overall success, problems arose that must be resolved before large-scale solar power becomes a reality.

Capturing energy from space and transmitting it to the ground is a concept that will back to 1923 when Russian theorist Konstantin Tsiolkovsky proposed mirrors in space that would direct powerful beams of sunlight toward Earth. In 1941, science fiction writer Isaac Asimov wrote a short story called “Reason” about microwave radiation from space that could be captured by a ground station and converted into electricity.

An illustration of massive solar panels in space with the curve of the Earth in the background.  A space shuttle flies alongside to provide scale.
This artist’s rendering shows a 1970s NASA vision for building solar-powered satellites using the Space Shuttle. (NASA/ESA)

The big advantage of placing power plants in orbit is that sunlight is up to ten times more intense in space because it does not pass through the Earth’s atmosphere. If a spacecraft is placed in the correct orbit, it can be continuously exposed to solar energy.

If successful, the result could be abundant, reliable, carbon-free energy, capable of powering a million homes with a single satellite.

The International Space Station is visible in the center frame with Earth in the background, rising from the bottom of the screen.
The International Space Station seen in 2011. Building the ISS required dozens of space launches, ultimately costing US$150 billion. Any solar-powered space satellite would need to be more than 10 times larger. (Paolo Nespoli – ESA/NASA via Getty Images)

This idea was considered in the early days of the space program because the basic technology required already existed in our current television and communications satellites. However, to produce enough power to be economically viable, these satellites would have to be very large – at least a kilometer on each side – so the cost of many space launches was deemed too high to be worth it.

For comparison, building the International Space Station took dozens of launches and 150 billion US dollars, and it is only the size of a football field.

A time-lapse video showing a box slowly extending its arms to form a square in a clean room.  A technician wearing a mask and hairnet stands behind the satellite.
Caltech researchers test DOLCE deployment technology. (Space Solar Energy Project/Caltech)

But now that the cost of spaceflight has been dramatically reduced thanks to companies like SpaceX, scientists are rethinking the idea. Groups in China, India, the United Kingdom and even the U.S. Naval Research Laboratory are working on their own space solar power technologies.

The Caltech device has been in the works since 2011. It was launched into space in January 2023 with a solar panel measuring just 1.8 meters. It carried a collection of 32 different types of low-cost solar cells, electronics to convert sunlight into microwaves, and two lightweight microwave transmitters that sent signals to the ground.

The biggest problem occurred during testing of their deployment technology when the cables used to deploy the structure in space got snagged, delaying the process. Fortunately, ground controllers were able to use the spacecraft’s cameras to identify the problem and ultimately resolve it. Then part of the structure jammed and operators had to mechanically vibrate the entire satellite to free it.

A colorful photo of the interior of an electronics enclosure, showing power transmitters and receivers illuminated by different colored lights.
A view inside MAPLE (Microwave Array for Power-transfer Low-orbit Experiment), the technology that wirelessly transmitted power from space in March 2023. (Caltech/Momentus)

But that’s precisely the goal of test flights: to identify problems and prevent them from happening again in the future.

If it’s difficult to deploy a lightweight structure less than two meters in diameter, imagine deploying something the size of a small city in space.

As the search for clean energy sources continues and the costs of climate change continue to rise, the price of building space solar power plants could become more reasonable, especially as we begin to look beyond the planet to meet our growing energy needs. .

WATCH | Animation and images of the Caltech deployment

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