Space-based solar power

Space-based solar power is an idea where we collect energy from the Sun in space using special satellites and send it to Earth. Because space has no air, these satellites can collect solar power more efficiently than panels on Earth. They change sunlight into other types of energy, like microwaves, which can travel through the air to special receivers on our planet.

In the 1970s, groups like the L5 Society began talking about using this technology for everyday energy needs. Later, people realized it could also be used as a tool for defending against missiles. This idea helped shape big projects in the 1980s, such as the Strategic Defense Initiative.

Recently, important tests have been done to see if this idea works. In May 2020, the US Naval Research Laboratory tested solar power generation in a satellite. In 2023, a project called MAPLE, supported by Donald Bren and his wife Brigitte, showed that it is possible to send power from space to Earth, though the amount was very small compared to regular communication satellites.

History

In 1941, the writer Isaac Asimov wrote a story called "Reason" where a space station collects energy from the Sun and sends it to planets. In 1958, the satellite Vanguard I used solar panels to power its radio. The idea of space-based solar power was first described in 1968. In 1973, Peter Glaser got a patent for sending power over long distances using microwaves. He worked with Arthur D. Little, Inc., and NASA studied the idea more in 1974. They found it had problems, like cost and lack of experience, but thought it was worth studying more.

From 1978 to 1986, the Congress and the Department of Energy worked with NASA to study this idea more. They spent $50 million and made many reports. The project stopped after the 1980 United States elections because there wasn’t enough information to decide if it was a good idea.

As of 2020, several countries like Japan, China, Russia, India, the United Kingdom, the US, and the European Space Agency are working on space-based solar power. In 2008, Japan made it a national goal. In 2015, China showed plans to build a space solar power station. They started building a testing base in 2019 and plan to launch a big station by 2035.

In 1999, NASA started a program to explore space solar power. They wanted to study how it could work, make designs, and plan for future technology. They looked at different ways to turn sunlight into electricity and send it to Earth. They thought space solar power might be a good option for the future because of its environmental benefits, but it needs cheaper ways to get materials into space to be practical.

In 2015, the Japan Aerospace Exploration Agency (JAXA) showed they could send power wirelessly over short distances. A company called Aetherflux is also working on this idea but changed its focus to data centers in space in December 2025.

Advantages and disadvantages

Space-based solar power has many good points. In space, the sun shines all day, every day, without clouds or atmosphere blocking the light. This means we can collect much more energy than we can on Earth. We could also send this energy where it is needed most, and it would not harm plants, animals, or add pollution to our air or water.

However, there are also some challenges. It costs a lot of money to build and send satellites into space. Keeping these satellites working can be hard because they are far away and we cannot reach them easily. Space is a tough place for machines, and old satellites could become space junk that floats around and hits other satellites. The ground stations to receive the energy would also be very large and expensive. There are also some losses of energy during the process of turning sunlight into usable power.

Design

Space-based solar power has three main parts:

1. Collecting sunlight in space using mirrors or special cells.
2. Sending the collected energy to Earth as invisible waves.
3. Receiving the energy on Earth with special antennas.

In space, these systems don't have to deal with weather or gravity, but they must handle space dangers like tiny space rocks and bright solar bursts. Scientists have studied two ways to change sunlight into usable energy: using special cells that turn light into electricity, or using mirrors to heat water and create steam power. Sending energy to Earth as invisible waves has been tested and shown to work.

One way to send energy from space uses invisible waves called microwaves. Tests have shown this works well over long distances. Another way uses lasers, which are beams of light. Lasers could be useful for powering equipment on the Moon or Mars, but need many satellites to work well.

Putting solar power stations in a special orbit around Earth makes it easier to keep them pointed correctly. Sending energy from this high orbit needs very large antennas, but it can provide almost constant power. Some ideas suggest starting with satellites in lower orbits before moving to higher ones.

On Earth, the energy would be received by large antenna systems made of many small parts. These systems could also help power spaceships or bases on other planets.

Launch costs

One challenge with space-based solar power is the high cost of launching things into space and the large amount of material that would need to be sent up.

Many materials don’t need to reach their final position right away, which means we could use slower but more efficient engines to move them into place. Possible options include ion thrusters or nuclear propulsion. Building the needed equipment—like solar panels, power converters, and transmitters—will be very expensive, and keeping everything working will cost even more.

To understand how big this challenge is, let’s look at an example. If a solar panel weighs about 20 kilograms for every kilowatt of power it can produce, a power station that can give out 4 gigawatts would weigh around 80,000 metric tons. That’s all the weight that would need to be launched from Earth right now. However, this is much heavier than what we usually send into space. As of 2015, spacecraft we’ve already flown weigh about 150 watts per kilogram. With new, lighter designs, we might get this down to just 1 kilogram per kilowatt, meaning the solar panels alone would weigh about 4,000 metric tons for the same 4-gigawatt station. We also need to add extra weight for getting the panels into the right position and keeping them there.

When thinking about these costs, we should also remember the environmental effects of launching so much material into space. For comparison, building a new coal or nuclear power plant on Earth costs between $3 billion and $6 billion for each gigawatt of power it can produce—though this doesn’t include the full environmental costs, like handling carbon dioxide emissions or storing used nuclear fuel.

Building from space

Gerard O'Neill suggested making solar power stations in space using materials from the Moon because it could save money. The Moon has less gravity and no atmospheric drag, making it easier and cheaper to launch things from there compared to Earth. This idea needed a big investment to set up special launch systems on the Moon.

Later, a new plan used machines on the Moon that could work by themselves, controlled from Earth. This would need fewer people in space. The Moon’s lower gravity would help make this easier and save energy.

Physicist Dr David Criswell also thinks the Moon is the best place for these solar power stations. He believes we could build them using materials found on the Moon, which would cut costs even more. This plan includes special machines that move around to build parts and send the power to Earth.

Some ideas also talk about getting materials from asteroids. One study looked at using a big machine in space to bring back a piece of an asteroid. This could lower launch costs a lot, but we still need to learn more about what these asteroids are made of before we can use this idea. Some suggestions include using asteroids like Apophis or 1999 AN10 to build many solar power stations.

Safety

One big worry with space solar power is how the strong microwave beams might affect people and animals on Earth. Even though the strength of these beams is lower than sunlight, microwaves can go deeper into our bodies. At certain levels, this could harm learning and memory.

To keep everyone safe, special designs are suggested to prevent the beam from pointing in the wrong direction. Aircraft can protect passengers inside, and controlled airspace can help keep other smaller aircraft away. Scientists are also studying how to make sure wildlife, especially birds, stay safe. One idea is to place the receiving stations far from land to avoid problems, though this brings its own challenges.

A safe method being studied uses a special system to keep the beam focused only where it should be. If anything goes wrong and the beam loses its guide signal, it automatically spreads out, preventing harm to anything outside the intended area. More research is still needed to understand how these beams affect Earth's upper atmosphere over time.

Timeline

In the 20th century

• 1941: Isaac Asimov wrote a story where a space station sends energy from the sun to planets using special beams.
• 1968: Peter Glaser introduced the idea of a satellite with solar panels in space to collect energy and send it to Earth.
• 1973: Peter Glaser received a patent for sending power over long distances using these special beams.
• 1978–1981: The United States Department of Energy and NASA studied the idea of satellites that collect solar power.
• 1987: Canada did an experiment called Stationary High Altitude Relay Platform.
• 1995–1997: NASA looked again at ideas and technology for collecting solar power in space.
• 1998: A study showed that satellites collecting solar power could work, but there were some challenges.
• 1998: Japan's space agency started working on a system to collect solar power from space.
• 1999: NASA began a program to explore space solar power.
• 2000: A NASA expert said that making these satellites work would need many new technologies and would take many years.

In the 21st century

• 2001: Japan planned to launch a small test satellite to collect solar power.
• 2003: Europe studied the idea.
• 2007: The US Pentagon said they wanted to get solar power from space to help with energy needs.
• 2007: A workshop was held at MIT to discuss the current state of space solar power.
• 2010: Professors announced a special session on sending solar power through the air at a big science meeting.
• 2010: India and the US started working together on collecting solar power from space.
• 2010: A book about space solar power as a step in the partnership between India and the US was published.
• 2012: China suggested working with India on a solar power satellite.
• 2015: Caltech and Northrop Grumman started a project to develop a space solar power system.
• 2015: Japan showed they could send small amounts of power from space to a receiver on Earth.
• 2016: A Chinese general talked about building satellites to collect solar power.
• 2016: A team from several US groups won a challenge to lead the way in space solar power.
• 2016: A group called Citizens for Space-Based Solar Power started petitions to get support for space solar power.
• 2016: Researchers showed that building many power satellites would not hurt Earth’s atmosphere too much.
• 2016: A new idea for a solar power satellite was proposed.
• 2017: NASA chose five new research ideas, including one about trends in space solar power.
• 2019: Researchers in Japan proposed a group of small satellites to send power to other satellites.
• 2019: China made a test center and planned to launch a big solar power station by 2035.
• 2020: The US Naval Research Laboratory launched a test satellite. The US Air Force planned to launch a test satellite called ARACHNE in 2024.
• 2021: Caltech planned to launch a test array by 2023.
• 2022: The UK planned to launch the first space power station by the mid-2040s to help meet the country’s energy needs.
• 2022: The European Space Agency proposed a program called SOLARIS to start using solar power satellites from 2030.
• 2023: Caltech’s test satellite sent a small amount of power to Earth.
• 2025: Researchers in London estimated that by 2050, space solar power could provide most of Europe’s renewable energy.

Non-typical configurations and architectural considerations

The usual idea for space-based solar power involves many large satellites in a special orbit around Earth, each collecting sunlight and sending energy to places that need it. These satellites are usually about 1 to 10 gigawatts in size and use solar panels to collect energy. They send this energy as radio waves to special receivers on Earth.

There are many other ways this idea could work. Satellites could be placed in different orbits, like closer to the Sun or on the Moon. Different methods to collect energy could be used, such as heating fluid to make steam or using lasers. Some ideas suggest using materials from the Moon or asteroids to build these satellites, or even making them in space using special machines. There are also many ideas for how to get the materials into space and set up the satellites, like using special rockets or even space elevators.