The April 1941 edition of Astounding Science Fiction includes Isaac Asimov’s tale “Reason,” which was eventually released in the collection I, Robot. The narrative in Asimov’s Robot series takes place on a space station that sends electricity in the form of microwaves to planets.
More than 30 years later, Peter Glaser, a NASA engineer who worked on, among other projects, the Apollo lunar landings, took a significant step towards making Asimov’s narrative device a reality. Glaser developed — and was awarded a patent for — a system that used satellite-mounted solar panels to convert solar energy to microwaves and then broadcast that energy down to Earth.
At the time, it was “conceptually possible” to conceive a system like Glaser’s in orbit, according to Harry Atwater, “but the cost of getting it there was prohibitive.”
Is space-based solar energy an expensive and risky pipe dream? Is it an effective strategy to tackle climate change? Although beaming solar electricity from space to Earth may eventually need sending gigawatts, researchers from Space Solar, the European Space Agency, and the University of Glasgow believe the process can be made surprisingly safe and cost-effective.
Beaming solar energy from space is not a new concept; since the 1960s, telecommunications satellites have sent microwave signals created by solar power back to Earth. However, delivering useful amounts of electricity is a very other thing. However, in recent years, space launch prices have dropped considerably, making the concept of beaming power from space to Earth much more viable. Atwater is part of a Caltech team that recently pulled it off. Or, at the very least, they proved that it was possible. In June 2023, they sent electricity from a spacecraft in space to a receiver on the top of their Caltech laboratory. It wasn’t a lot of energy—just enough to power two LEDs—but it was a significant step. Paul Jaffe, an electrical engineer at the United States Naval Research Laboratory, works on comparable technologies and has contributed to many of the technological discoveries that have enabled this.
Space-based solar power is a beautiful and tantalising concept, and some think that it is a goal worth realising. A massive constellation of satellites in geosynchronous orbit (GEO) almost 36,000 kilometres above the equator may collect sunlight unfiltered by the atmosphere and uninterrupted by darkness (save for up to 70 minutes per day around the spring and autumn equinoxes). Each megasat could then transform gigawatts of electricity into a microwave beam that was accurately directed at a large field of reception antennas on Earth. These rectennas would then transform the signal into usable DC power. The hundreds of rocket launches required to launch and sustain these space power plants would emit large amounts of soot, carbon dioxide, and other pollutants into the stratosphere, with undetermined climatic consequences. However, this may be offset in principle if space solar replaced fossil fuels and aided the world’s transition to clean power.
“The idea has been around for just over a century,” said Nicol Caplin, a deep space research scientist at the ESA, during a Physics World podcast. “The early notions were definitely sci-fi. It’s based on science fiction, but there’s been a fluctuation in interest since then.” The dazzling image has sparked several future ideas. Japan’s space agency has developed a roadmap for deployment. China’s space officials plan to launch a tiny test satellite into low Earth orbit (LEO) later this decade. Megawatt-scale systems in GEO in the 2030s have been proposed, but have yet to be financed.
The US Naval Research Laboratory has previously transmitted over a kilowatt of electricity between two ground antennas roughly a km apart. It also launched a satellite in 2023 that utilised a laser to broadcast around 1.5 watts, despite though the beam went less than 2 meters and the device was only 11% efficient. Caltech researchers completed a mission earlier this year that employed a miniature satellite in low-Earth orbit to test thin-film solar cells, flexible microwave-power circuits, and a compact collapsable deployment mechanism. The energy delivered Earthward by the ship was insufficient to operate a lamp, but it was progress nonetheless.
In 2022, the European Space Agency (ESA) launched Solaris, a space-based solar-power initiative, with an uplifting (but wholly fictional) animated movie. Sanjay Vijendran, the program’s director, told IEEE Spectrum that the effort’s purpose is not to create a space power station. Instead, the program intends to spend three years and €60 million (US $65 million) to determine whether solar cells, DC-to-RF converters, assembly robots, beam-steering antennas, and other critical technologies will improve dramatically enough over the next ten to twenty years to make orbital solar power viable and competitive. Low-cost, low-mass, and space-hardy versions of these technologies would be required, but engineers trying to draw up detailed plans for such satellites today find no parts that meet the tough requirements.
The Solaris initiative is exploring two possible technologies, according to Sanjay Vijendran – one that involves beaming microwaves from a station in geostationary orbit down to a receiver on Earth and another that involves using immense mirrors in a lower orbit to reflect sunlight down onto solar farms. He stated that he believes both of these methods have potential value. Microwave technology has sparked widespread attention and is the primary focus. It has huge promise, but high-frequency radio waves can also be exploited.
However, there are significant physical challenges to effectively creating a solar power plant in space. According to senior reporter Elizabeth Gibney’s Nature article, the solar array for an orbiting power station generating a gigawatt of power would have to be larger than 1 square kilometre if microwave technology was used. “That’s more than 100 times the size of the International Space Station, which took a decade to build.” It would also have to be built robotically because the orbital facility would be unmanned. The solar cells would need to withstand space radiation and debris. Gibney said that they would also need to be efficient and lightweight, with a power-to-weight ratio 50 times greater than that of a normal silicon solar cell. Engineers must also examine how to keep the cost of these cells low. Reducing losses during electricity transmission is another difficulty, according to Gibney. The ESA recommends increasing the energy conversion rate to 10 to 15%. This would necessitate technological improvements.
Space Solar is developing a spacecraft named CASSIOPeiA, which Physics World describes as “like a spiral staircase, with the photovoltaic panels being the ‘treads’ and the microwave transmitters—rod-shaped dipoles—being the ‘risers.'” It has a helical form and no moving components. These schemes include enormous amounts of microwave or radio radiation. However, space-based solar power is generally safe. For microwave radiation from a space-based solar power system, “the only known effect of those frequencies on humans or living things is tissue heating,” Vijendran stated. “If you were to stand in such a beam at that power level, it would be like standing in the evening sun.” However, Caplin stated that additional research is required to determine the impacts of these microwaves on humans, animals, plants, satellites, infrastructure, and the ionosphere.
These launches will be costly, in addition to their environmental impact. According to Caplin, the biggest impediment to developing a space solar power plant has always been cost. “As the landscape changes and goods become more affordable to transport to space, we may revisit the idea. Money speaks. We have the advice of two independent cost-benefit assessments, both of which concluded that this may be viable.” Space-based solar power would incur manufacture, maintenance, and launch expenses. Vijendran believes the cost of space-based solar power will ultimately decrease to a level that is competitive with solar and wind power on Earth, which is less than $50 per megawatt-hour. According to the Energy Information Administration’s 2023 report on the issue, solar electricity and onshore wind will cost between $20 and $45 per megawatt-hour in 2024.
There is more that may go wrong. Let us start with temperature. With gigawatts of electricity flowing through the system, heat removal will be critical because solar cells lose efficiency and microcircuits fry when temperatures rise too high. A few of dozen times a year, the satellite will abruptly enter the complete darkness of Earth’s shadow, causing temperatures to vary by roughly 300 °C, much above the ordinary functioning range of electronics. Thermal expansion and contraction can cause big structures at the station to bend or shake.
Then there’s the physical cost of functioning in space. Vibrations and torques from altitude-control thrusters, along with solar radiation pressure on the large sail-like arrays, will cause the station to bend and twist in various directions. Man-made debris and micrometeorites, as well as a faulty construction robot, will inevitably strike the huge arrays. As the number of space power stations grows, so will the potential of Kessler syndrome, an uncontrolled sequence of accidents that every space operator fears.
Probably the most difficult technological barrier to space solar power is a simple one: shaping and focussing the beam. The transmitter is not a dish, but rather a radio telescope in reverse. It’s a phased array, which consists of millions of small antennas that must operate in near-perfect synchronisation, each contributing to a collective waveform directed at the ground station. Coordination of a phased array, like individuals in a stadium crowd lifting their arms on cue to make “the wave,” is critical. It will only function effectively if each element on the emitter syncs the phase of its emission to perfectly correspond with the transmissions of its neighbours and an incoming beacon signal transmitted by the ground station. Picosecond-level phase faults might cause the microwave beam to blur or wander away from its intended target. How can the system synchronise pieces separated by up to a km with such remarkable precision? If you know the solution, please patent and publicise it, since engineers are currently puzzled by this topic.
There’s no disputing the allure of looking to outer space for limitless power. However, nature has a vote. As Lao Tzu famously stated in the Tao Te Ching, “The truth is not always beautiful, nor beautiful words the truth.”
Author- Amar Chowdhury
