Q. Could you explain the Space Solar Power Systems project.
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.
Q. Where does the idea for SSPS come from?
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.
Q. What is the progress status of SSPS in Japan?
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.
Q. How would SSPS contribute to our daily life?
Laser beam-type SSPS
SSPS will provide a great boost to the world's energy supply because power can be generated as long as the sun is there. So, in that sense, our daily life will directly benefit from the technology because SSPS will satisfy the demand for electrical energy.
Also, I believe that this technology will be useful in disaster situations. At the SSPS microwave receiving site, we use a flat-plane antenna called a "rectenna" (rectifying antenna) to convert microwaves into electrical energy. So, for example, if a blackout occurs due to a natural disaster, a thin, portable rectenna can be unfolded and deployed to receive microwaves from space, which can be converted into electrical energy.
Finally, in order to construct a structure as large as the SSPS in space, it will be essential to have a new space transport system and sophisticated robots. I think the SSPS project will push forward R&D in the rocketry and robotics fields, which will inevitably contribute to the growth of both industries.
Q. Are there any safety concerns about electrical power transmission via microwave or laser beams?
We intend to make the intensity of the energy of the microwaves similar to that of sunlight. However, it is necessary to take strong measures to ensure the safety of living organisms on Earth in case they are exposed to microwave beams that are misaligned with the receiving site on the ground. For example, even with weak microwaves, the impact of prolonged exposure on the human body has not yet been fully understood. So I think it is essential to take operational measures to ensure the safety of the surroundings of the receiving site.
Similarly, there must be strict safety measures for the use of laser beams. For example, the SSPS station would transmit a laser beam aiming at a navigation signal light on the ground. If the power transmission facility shifts in space and the navigation signal is interrupted, transmission should be stopped immediately.
Q. Is there any international research collaboration on SSPS?
We have not really discussed it yet because SSPS is still under basic study, and Japan is the only country that is proactively dedicating itself to the research, by carrying out demonstration tests, for instance. Having said that, though, in reality, the enormous costs will make it very difficult for Japan to make the project happen independently, so I think that we will eventually need to run the project at an international level.
Q. Could you tell us what your goal is now.
I believe that Japan's long-term, steady efforts in SSPS research have made us the leading country in the field. I would like to carry on technology demonstration, step by step, in order to put the technology into practice in the future.
Although, Japan depends on imported energy resources today, if we can establish SSPS technology, it may even become possible for us to become an energy exporter. We would like to continue to lead the world in SSPS technology development, so that Japan will be able to play a major role as a contributor to the world's energy supply.
Advanced Missions Research Group, Innovative Technology Research Center, JAXA
Mr. Fukumuro joined the National Space Development Agency of Japan (NASDA, now part of JAXA) in 1981, and has since worked in project planning and management, public information, and financial accounting systems. He has been in charge of research planning for the Space Solar Power Systems (SSPS) since 2007.