Since the disaster in Fukushima, Japan’s review its policy on nuclear power was yet one of its strategic priorities. The development of new energy sources that respect the environment has become even more pressing, and some Japanese scientists believe the solution to this problem could come from space. JAXA (Japan Aerospace Exploration Agency) studies because the concept of space solar power that could, according to his supporters, becoming a major energy resources in two decades.
The concept of space solar power is to collect the sun’s rays with large reflectors placed in geostationary orbit and then send that energy in the form of microwaves or laser facilities to the ground where it is used to produce electricity or hydrogen. Since the collection of sunlight is outside the atmosphere, it is very efficient and not influenced by the weather (rain, clouds, etc.).. In addition, the facilities are located in geostationary orbit, they can generate power almost continuously, while the solar panels on the ground are dependent on time of day and seasons.
The idea of generating electricity in space was presented for the first time in 1968 by Peter Glaser, an American scientist. NASA has done research on this subject in the 1970s but the project was abandoned a decade later because of its excessive cost. Since the late 1990s, the United States interested in this new concept, but achieving significant progress. For its part, Japan has started in 1998 studies on SSPS (Space Solar Power Systems) that continue to this day. JAXA since 2008 carries the same experiments to develop technologies for power generation in space. Through his involvement in sustainable, Japan has become the leading country in research on space solar power.
JAXA has not yet decided if the energy in orbit will be transmitted to Earth by microwave or laser and examines the two options. Regarding systems SSPS microwave, two concepts are studied: the basic model and advanced model. The basic model consists of a large sign hanging from a satellite cables. One side of the panel generates energy and transmits the other side on the ground. The advanced model is a combination of two mirror reflectors 2km in diameter flying in formation with a system consisting of two solar power generators attached to a panel of the microwave transmitter. The advanced model is a technological challenge, but he can point to the Sun and thus offers better performance than the basic model. The microwave beam sent from space to the ground is received and converted into electricity by a rectifying antenna 2km in diameter. SSPS laser system studied by JAXA consists of mirrors focusing sunlight on a semiconductor device that converts sunlight directly into laser beams. The technologies required for the laser SSPS are however very complex and their development would pose more difficulties than that of SSPS microwave.
Currently, four major research activities associated with the SSPS are conducted by JAXA. The first floor is the demonstration of wireless power transmission by microwave and laser. JAXA will test technologies including training and pointing of a beam of microwaves (on the order of kW) over a distance of 50m. Research will also be conducted to develop a technology to directly convert sunlight into laser beam. The second research topic is the development of technologies for building structures of a few hundred meters for both a panel with a thickness of 0.1 m and a lightweight mirror with a density of 300g/m2. These technologies will be built at first experienced on the ground. The third line of research is the preparation of experiments demonstrating wireless power transmission in orbit. Experiments transmission power of the order of kilowatts from space to ground and will be carried out. A small scientific satellite currently under development at the JAXA module or JEM (Japanese Experiment Module) of the International Space Station will serve as a platform for these tests. The fourth area of study is to establish a realistic roadmap for a market an SSPS in the 2030s.
JAXA has started the development of demonstration systems on the ground of the wireless transmission of energy of 1 kW, both microwave and laser. These experiences should be completed late 2013. Based on the design of the demonstration system on the ground, experience power transmission by microwaves from space will be made around 2015. If the technologies needed to release a laser are ready for that time, they will also be tested from space. When the experiences of power transmission to the ground and in orbit are completed, the choice between microwave and laser will be made. Following this selection, JAXA will embark on a demonstration of about 100 kW in space. At this stage, all the core technologies have been verified and the system configuration is selected commercial SSPS. The estimated cost of energy production and acceptance of this new technology by the public will be important factors in this decision. Testing for commercial SSPS will be done with facilities capable of producing first 2MW (2020) and 200MW (2025). The construction of an SSPS for commercial production of 1GW of electricity would have to start in the 2030s.
The roadmap of JAXA seems very optimistic, considering the obstacles facing this project. First, there is the cost of access to space. A reusable launch vehicle is thus needed to demonstrate the small central 2MW 2020, and an orbital transfer vehicle will be required for large central 200MW by 2025. Meet these requirements will be very difficult, but researchers believe that the JAXA these goals are achievable if the community of space transportation is seriously addressing the problem. Finally, the budget for this work does not seem up to the activities in the roadmap. JAXA is currently maintaining a minimum level of research and development in the field of SSPS, but there is no guarantee the availability of a budget for the following years.