The idea of harvesting solar energy from space may sound like science fiction and, furthermore, it would make all the sense in the world for it to do so: Isaac Asimov already wrote about it in his story “Reason” of 1941. However, the scientific community has been ruminating on it since 1968, when American aerospace engineer Peter Glaser published the first technical article on this concept in Science magazine.
Since then, entities such as NASA, the California Institute of Technology or the Japanese Japan Space Systems have explored the possibility. However, Japan is the closest to achieving what no one has yet achieved: generating electricity in space and sending it directly to Earth.
Context. To begin with, the cost of launching rockets has become enormously cheaper since the idea began to be glimpsed. On the other hand, we are in the midst of global energy transition from mobile fuels towards renewable sources where there is one that stands out: solar energy.
But solar energy requires space to deploy parks with photovoltaic panels, which is why China is choosing to assemble them in the open sea, Germany explores with lakes and Japan… Japan is an island with little space. On the other hand, solar energy has another important limitation: it only works when there is sun. However, in space there are no clouds or night and the sun shines without stopping.
Why is it important. Because the business models that J-spacesystems is developing They are designed to generate about one gigawatt of constant power. To better understand the dimensions of that figure, it is the energy necessary to cover 10% of the consumption of a megacity like Tokyo and is also equivalent to the power of a standard nuclear reactor.
We are facing a paradigm shift in energy density: a solar plant in space capable of ‘redirecting’ its energy beam towards different receiving antennas according to demand, whether within the country itself or the world. This opens the doors to sending energy to areas in emergency situations or meeting consumption peaks, something that is not possible with the current infrastructure.
Japan Space Systems Scheme
What is Ohisama. Ohisama is sun in Japanese and it is also the name of a Japanese satellite of 180 kg that has an integrated solar panel approximately the size of a door (70 cm x 2 m) is to orbit at 450 km altitude, where it will be able to generate 720 watts of electricity that it will then convert into microwaves. It will then launch those microwaves up to a 64-meter antenna in Nagano. If the energy arrives, it will be converted into electricity. The ultimate goal: light an LED. Yes, all this to light a light bulb.
In reality, the important thing is not so much the power transmitted in the test (which is very small) but rather being able to validate that the transmission works through the ionosphere. It is the test of truth: in 2024 Japan has already tried it successfully from a plane seven kilometers high, but this is already a jump to a real orbit that will allow everything to be scaled (if it goes well).
When and where. From now on, literally: The window for the third attempt began on February 25, with a backup date until March 25. The launch site will be the Kii Spaceport in the city of Kushimoto, Wakayama Prefecture, the first private rocket launch site in Japan.
What comes next. If the experiment goes well, Japan would go on to implement those commercial models, which consist of 2.5 square kilometer solar panel arrays in geostationary orbit at 36,000 km with 4 km diameter receiving antennas on the ground. The estimated date for its commercialization is from 2040 and in addition to supply on land, Japan has in mind to use the system for energy supply in lunar exploration missions.
Why is it so difficult. The first immediate risk inherent to the project is Kairos 5 of Space Onethe private Japanese company in charge of putting Ohisama into orbit: the two previous launches failed. Third time lucky? The possibility of another company from outside doing it is not an option (at the moment). As explains Yanagawa of J-spacesystems: “Although overseas rockets were an option, we selected Kairos following the national policy of supporting Japan’s private sector launch capabilities.”
But even if the launch were successful, the big problem will be microwave diffraction: transmission over thousands of kilometers risks scattering, requiring huge transmitting antennas and very precise phase control. Japan has been working to solve this bottleneck for decades.
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Cover | Hunini CC BY-SA 4.0 and Nuno Marques
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