The Space Energy Industry: will it give us an emissions-free future?
Over the past 5 years, we have witnessed how space energy has turned from science fiction into an object of deep R&D. What's next?
The concept of power plants in space has been around since 1941, when Isaac Asimov published his science fiction novel “Reason”. In the story, a space station transmits energy collected from the Sun to various planets using microwave beams. The technical details behind this idea were further developed in the 1970s, but it was abandoned due to high costs. A space-based solar power station would require heavy structures in Earth orbit, which was not economically viable due to the payload delivery prices of that time. Today the situation is different. So let’s see what is going on with the energy industry in space.
Why do we need energy in space?
The primary reason for the emergence of the energy industry outside our planet is the swift development of the space industry, which we wrote about in our previous post. The second reason is to deliver clean, cheap energy to Earth from space and offset carbon emissions. Finally, efficient extraterrestrial energy sources are paramount for the development of Moon bases and colonies on Mars. Read more about Moon bases in one of our previous articles.
Today’s options: nuclear and solar
Transporting batteries or fossil fuels from Earth to other planets or for long distance space travel is currently not cost-effective. If we limit our thinking to realistic industry developments over the next 30 years, we find that there are currently only two ways to supply energy in space. Solar energy is relatively cheap and is suitable for missions near the Earth or Mars orbit. Only one aerospace manufacturer, Rocketlab, routinely provides solar panels with a power generation rate of 1 MW/year, which is enough to support hundreds of satellites.
As we move beyond Mars, the sunlight intensity decreases by >2x compared to Earth and we need to switch to nuclear power. This approach was used on Voyager which is still successfully transmitting signals back to Earth after 45 years of space travel. The main limitation of nuclear power devices most commonly used today in space is low output - enough only to boil a single kettle or to support a small space probe.
There are multiple options to explore beyond the 30 years horizon, such as mining hydrogen from asteroids’ ice to use in hydrogen engines, using liquid hydrogen from the gas giants or nuclear fusion. These are still at the early stages of development and we will cover advances in these areas in one of our future posts.
NASA is going nuclear
New ambitious projects like Artemis require more power and control over nuclear reactions. That's why NASA is betting on power plants that carry out controlled nuclear fission in a chain reaction. Initially, NASA and the US Department of Energy worked together on the Kilopower project to demonstrate a simple reactor's capability to generate 10 kW in the lunar environment. NASA has now awarded 12-month contracts to Lockheed Martin, Westinghouse, and a joint venture between Intuitive Machines and X-Energy to further develop the design to 40kW.
In principle, it is possible to build a larger nuclear reactor in low Earth orbit for the needs of terrestrial or orbital users in order to remove dangerous power plants from the Earth surface. Relaxing safety requirements to simplify the design could offset the cost of getting the station into orbit. Who will be the first to try?
China is leading the way for space-based solar power
Unlike NASA, other national agencies such as China's CNSA, Japan's JAXA, Europe's ESA and Britain's BEIS see solar power as the main solution for commercial-scale orbital power plants. China is closest to the practical implementation of a space-based solar power plant with announced satellite testing in 2028, delivering megawatt-level power (enough to power 100s homes) to military and civilian customers in 2035, and generating about two gigawatts in 2050 (which will place it as 5th largest on Earth today). Space-based solar power is attractive due to the all-day availability of solar light in orbit and the absence of clouds and the atmosphere which absorb at least 30% of incoming light even on a sunny day at the equator. All of these factors make solar power in space almost 10x more powerful than the one on the ground.
How do we send energy back to Earth from orbit or transmit to other orbital users?
Whatever source of energy becomes preferred for orbital power plants, it will be necessary to deliver the energy to consumers. Today, microwaves are considered the most suitable means for this. Microwaves are not attenuated by clouds, are easy to generate at high powers, and are relatively easy and safe to receive with a rectenna array (a special type of antenna that converts microwaves to direct current). As recently shown in the SCOPE-M project, the efficiency of transmitting 1 kW of power at 10 GHz over a distance of 1 km is 60%. The technology is ready to scale to higher powers and distances up to 400 km, which is enough for a low Earth orbit power plant.
At longer distances the microwave beam will broaden and require a receiver antenna larger than a kilometer, regardless of the transmitted power. An alternative is to use a concentrated laser beam. PowerLight Technologies has already demonstrated the transmission of 400 W laser power over a distance of one kilometer. We expect lower laser energy transfer efficiency, which would make it a poor solution for industrial scale energy needs. However, there may still be niches for lasers at lower energy scales or longer distances or in situations where smaller receivers are required, such as orbital power consumption.
Over the past 5 years, we have witnessed how space energy has turned from science fiction into an object of deep R&D. Some technologies, such as satellite solar panels and small nuclear reactors, are already being commercialized. Further space exploration will increase energy demands to the gigawatt scale. For long-term sustainability we should consider using asteroids or lunar regolith as potential sources for plant construction in space.
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Wow, I thought that such projects are pure science fiction. The future is closer than I thought:)
Solar power with microwave transfer to Earth was first proposed I think in the 60-ies and was studied by US DOE in late 70-ies - early 80-ies. Other countries looked at it through the years. There's a number of problems that need to be solved: LEO solar power satellite would only spend a few minutes per pass over a ground based rectenna. A phased array antenna can increase it some. Placing satellite in higher orbit increases spread of microwave beam, there's a fundamental wavlength over aperture diffraction limit. Cost of antennas and rectennas was quite high but maybe not prohibitive these days. There were questions regarding power density that can cause non linear effects in ionosphere. Maybe these problems were solved since I looked at this many year ago :) BTW there were interesting studies about building solar power stations on the Moon