Introduction of Research

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About the SSPS

Many studies have been conducted on SSPS concepts and technologies in Japan and overseas. The section summarizes the history, advantage, and challenges of the SSPS.

History of the SSPS (previous conceptual studies)

First SSPS idea
SSPS concept proposed by Dr. Peter Glaser of the United States in 1968
Glaser, P. E.,
“Power from the Sun; It's Future,” Science, 162, pp.857-886, 1968

The concept of the SSPS was first envisioned by Dr. Peter Glaser of the United States in 1968. His idea was to deploy enormous solar panels in space together with a very large antenna to transmit the collected energy as microwave power. The solar energy would be converted into electricity, converted again into microwaves, and beamed to a receiving antenna, or rectenna, on the ground. The rectenna would then convert the microwaves back into electricity to be used as an energy source. Encouraged by the success of the Apollo Program and human spaceflights, the NASA in the US began to explore methods for constructing large-scale space structures using astronauts. Interest in the idea grew further throughout the world when the first energy crisis struck several years later.

Scientists in the U.S. and Europe have proposed various SSPS concepts over the decades since Dr. Glaser proposed the idea. Yet financial constraints and a lack of political momentum in those countries have forced their research to a standstill. Japan is still working on SSPS concepts and technologies.

NASA Fresh Look
A new SSPS concept was developed using technologies available in the 1990s under the NASA's SSP Fresh Look Study.
John C. Mankins, “A fresh look at space solar power: New architectures, concepts and technologies," 1998
During 2011-2012, NASA investigated a new concept of space solar power: SPS-ALPHA.
John C. Mankins, “SPS-ALPHA: The First Practical Solar Power Satellite via Arbitrarily Large Phased Array,” 2012
European research on the SSPS
The European Space Agency (ESA) and German Aerospace Center (DLR) carried out SSPS research activities in the mid-2000s.
European Space Agency

Japan commenced its SSPS research activities in the 1980s. Under leadership of the Institute of Space and Astronautical Science (current JAXA ISAS), an industry-government-academia research team introduced a conceptual design of a 10,000 kW-class “SPS2000” in the 1990s. In the 2000s, JAXA and the Ministry of Economy Trade and Industry (METI) studied a million kW-class SSPS concept.

Solar cell units are mounted on the two faces of a triangular prism, and a transmission antenna is equipped with the remaining face. It was to be launched into equatorial low earth orbit and send energy to equatorial rectennas on the ground.
Achievement report of a commissioned task by New Energy and Industrial Technology Development Organization (NEDO) “Space Solar Power System Research” in 1993.
SSPS study by METI
The METI commissioned the SSPS research to the Institute for Unmanned Space Experiment (current Japan Space Systems or J-spacesystems). They adopted a panel-shaped system that integrated a solar panel for power generation and a microwave antenna for transmission. The system is projected to produce a million kW on the ground.
Image credit: J-spacesystems
A million-kW microwave SSPS model
This concept was studied in the 2000s under the leadership of JAXA. The system consists of two reflecting mirrors, one main spacecraft with solar panels, and a microwave transmission device.

Researchers assessed SSPS concepts by closely considering the social demand and readiness of the technologies.

SSPS advantages and challenges

The table below lists the major advantages and challenges of the SSPS.

  Advantages Challenges
  • Unlike terrestrial renewable energy sources, the SSPS provides power 24 hours a day under all weather conditions.
  • The solar irradiance in space is 40% stronger than that on the ground.
  • Power can be directed to different locations on demand (eliminating the need for power lines).
  • The development of space transportation technology for launching bulky materials, technology for assembling large structures in orbit, and technology for in-orbit operations and maintenance (repair) over many years.
  • The development of technology to generate, transmit, and receive power efficiently and safely.
(environmental impacts, etc.)
  • The SSPS emits no greenhouse gases and produces no hazardous waste to generate power.
  • The SSPS is less vulnerable to terrestrial natural disasters (such as earthquakes).
  • The potentially adverse effects of microwaves/lasers on human health, the atmosphere, the ionosphere, airplanes, electronic appliances, etc.
  • Measures to prevent, withstand, and repair damage by space debris, solar flares and so on.
  • Strategies for handling a non-operational SSPS, including removal from orbit or recycling.
  • No fossil fuels are purchased to generate power.
  • Unlike fossil fuels, solar energy is not affected by fluctuations in energy prices associated with regional conflicts and supply shortages.
  • Costs associated with space transportation, orbital assembly, operation and maintenance, and removal must be reduced to compete with other energy sources.
  • Microwave frequencies, orbital slots, and terrestrial rectenna sites must all be secured.

Basic Plan on Space Policy (Provisional Translation)

The Basic Plan on Space Policy determined by the Strategic Headquarters for Space Policy on January 9, 2015 describes future initiatives for space utilization:

iii) initiatives aimed at expanding future space utilization, II. Strengthening the Industrial/Science and Technology Infrastructure, (2) Concrete Approach

Research shall focus on not only a space-based solar power system with the potential to solve global challenges in fields such as energy, climate change, and environmental crisis, but also space initiatives to improve quality of life and lead to the creation of more vibrant future and more detailed observations of solar activity, the effects of solar-induced changes in space weather patterns on our spacecraft, and the results of the countermeasures we take.

The Basic Plan on Space Policy, the Strategic Headquarters for Space Policy