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Laser beam-type SSPS
The Space Solar Power Systems project is a space-based solar power plant that generates energy by collecting sunlight in geostationary orbit. The energy is then transmitted to the ground, and converted into electricity and hydrogen for practical use. SSPS consists of a space-based power generation/transmission facility that gathers sunlight, converts it into microwaves or laser beams, and transmits those to the ground; and a power receiving facility on the ground.
There are differences in characteristics and capability between microwaves, which are used in microwave ovens and cellular phones, and laser beams, which you commonly see in computer printers and presentation pointers. We have not yet decided which of the two to use with SSPS, or whether we will somehow combine them. We are currently conducting ground-based experiments to find the most efficient way to transmit energy.
Regardless of which transmission technology we use, when we collect sunlight from outside the Earth's atmosphere, we can get a continuous supply of it, with almost no influence from the weather, the seasons, or time of day, allowing very efficient collection of solar energy. And since the energy source is the sun, it's an endlessly renewable resource - it won't run out as long as the sun is there. Also, because the power is generated in space and carbon dioxide is emitted only at the receiving site, emissions within the Earth's atmosphere can be greatly reduced, which makes this technology very friendly to the environment.
The idea for space-based solar power generation was introduced by an American, Dr. Peter Glaser, in 1968. His idea was to deploy large solar panels in space for power generation, and convert the energy into microwaves to transmit to the ground. NASA and the United States Department of Energy looked into the implications of implementation. But the project was so costly, it was shut down during the Reagan administration in the 1980s. Meanwhile in Japan, probably reflecting our nation's shortage of energy resources, SSPS research was started early, and has since been pursued by many universities and JAXA.
There are many technological challenges to solve before SSPS can be implemented. However, in principle, we are getting close to the stage where it is feasible, and we have just moved from the study phase to the technology demonstration phase. Researchers have started preparation for the world's first demonstration of 1kW-class wireless power transmission technology, and are aiming for practical use in the 2030s. At this point, you could say that Japan is leading the world in SSPS research. I think that this is all thanks to JAXA's long-term commitment to this research. Q. Could you describe the advantages of Japan's SSPS technology. When transmitting power by microwaves, a significant technological challenge is how to control the direction, and transmit it with pinpoint accuracy from a geostationary orbit to a receiving site on the ground. Transmitting microwaves from an altitude of 36,000 kilometers to a flat surface 3 km in diameter is like threading a needle. In my opinion, Japan currently has the most advanced technology to do this.
With laser beams, as with microwaves, large reflectors will be used to collect sunlight. But uniquely, the energy of the sunlight itself will be used at the collection point as excitation energy for the laser beams. This would allow us to keep the structure simple, and therefore reduce the size and weight of the orbiting power plant.