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The European Space Agency plans to build solar power stations in space to deal with the energy crisis, but construction costs seem to limit the development of space-based solar energy. However, the advent of recyclable rockets has made space-based solar power possible.

/ photos by Stuart Clark (Stuart Clark)

Translation | Ma Jun

Editor | Wen Jing

The original article is published in Science focus 2023.05.

In late November 2022, the Council of Ministers of Science and Technology of the European Space Agency (ESA) met in Paris and set out the priorities of ESA's work for the next three years. One of them is related to the current and even future global hot issues-energy issues. ESA decided to implement the "Space-based Solar Energy" (Solaris) program to rid Europe of fossil energy shortages and ensure the energy security of ESA member states. To put it simply, the plan aims to study the feasibility of building a space-based commercial power station in orbit.

According to the space-based solar energy program, these power stations will use huge solar panels to absorb more solar energy, convert it into electricity and transmit it to Earth in the form of microwaves. On the other hand, the ground receiving station receives the microwave through the huge antenna, and then the power transmitted by the microwave is directly input into the power grid.

It sounds like a plot from science fiction. But Sanjay Vijandran (Sanjay Vijendran), a scientist at ESA, says scientists have been trying something similar for the past 60 years. Because communication satellites can generate electricity through solar panels and rely on it to transmit signals to the earth. On the ground, these signals are converted into electrical signals for data interpretation. "the physical principles involved in the transmission of signals by communication satellites are exactly the same as those involved in space-based solar power generation, but the scale of power generation is very different." Vijendran explained.

Space-based solar power stations can be achieved at a freight rate of $300 per kilogram to reach the scale of commercial power generation, requiring solar panels thousands of meters long, more than 10 times the total length of solar panels on the International Space Station. The solar panels will be installed by robots in space 36000 kilometers above the earth's surface. This altitude is in the same orbit as the communications satellite, so that the solar power station can remain relatively stationary with the ground receiving station, which is convenient for energy transmission.

That sounds hard to achieve. At present, however, the only obstacle to building space-based in-orbit solar power stations is the cost-the cost of transporting construction materials into space is too high. Typically, the cost of transporting goods into space is about $1000 (7200 yuan) per kilogram, but given the sheer size of space-based in-orbit solar power stations, they are more expensive to build and have an unreasonable input-output ratio and cannot be commercially available.

However, space costs are falling sharply as SpaceX's recyclable rockets are increasingly used in space. "the shipping cost of $300 (about 2200 yuan) per kilogram is good news for the construction of space-based solar power stations." Said John Mankins, a former NASA physicist who is now president of Artemis innovative Management Solutions.

Mankins, a well-known expert in solar power satellites, has previously believed that the cost of transporting construction materials is a limiting factor for space-based solar power. But this constraint will not exist for much longer. "the shipping cost of $300 per kilogram will become a reality in the next five to seven years," Mankins said. "

For this reason, ESA is working with relevant European manufacturers to design two solar power satellites. In addition, ESA has launched a research and development program on solar cells and large antennas to make solar-powered satellites lighter and more efficient.

The prospect of space-based solar technology that experimental satellites have been able to transmit energy to the ground is so promising that similar research is being carried out not only by ESA but also by other agencies and companies.

In September 2021, Frazer-Nash, a British consultancy, submitted a report to the British government, suggesting: "Space-based solar energy projects are technically feasible, affordable, sustainable economic benefits for the UK and contribute to the goal of net zero emissions." The British government has announced that it will fund 4.3 million pounds (40 million yuan) to explore space-based solar energy with a view to providing cleaner and cheaper energy and improving Britain's energy security.

China is also promoting the development of this technology and plans to complete a feasibility study on air-to-ground energy transmission by 2028. At present, China's plan is to verify the technical feasibility, not to build a real commercial space-based solar power station. However, once the experiment is successful, it will have a landmark impact on the development of space-based solar technology.

On January 3, 2023, a research team at the California Institute of Technology launched an experimental satellite called Space Solar Power Demonstrator, or SSPD, to verify the technology needed for operational in-orbit solar power stations. On June 1, the California Institute of Technology announced that the satellite had directed the energy of the microwave beam to targets in space, and even sent some of the energy to Earth's probes.

"obviously, we need to work harder." "the space-based solar energy program is of great significance for us to verify the feasibility of solar power generation in space, and will also promote follow-up research," Vijendran said. "

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