Japan reaches for stars to develop orbital solar

Researchers at the Japan Aerospace Exploration Agency (JAXA) are aiming to develop a 1 GW space-based commercial solar power system by the 2030s.

In a recent report in IEEE Spectrum, the magazine published by the Institute of Electrical and Electronics Engineers (IEEE), Susumu Sasaki, a professor emeritus at JAXA who spent much of his 41-year career researching space-based solar power systems, examines the agency’s technology road map for a series of ground and orbital demonstrations that could lead to the development of the 1 GW system (which would have about the same output as a typical nuclear power plant.

The JAXA plan foresees the creation of a series of geosynchronous-orbiting satellites that collect solar power and beam it back to Earth. The agency is currently working on different models. In one model, a one-sided PV panel measuring 2 kilometers per side with transmission antennas on its bottom would be suspended by 10-kilometer-long tether wires from a small bus, which would house the satellite’s controls and communication systems.

However, the problem with this solar power satellite (SPS) configuration would be an inconstant rate of power generation, Sasaki writes. "Because the photovoltaic panel’s orientation is fixed, the amount of sunlight that hits it varies greatly as the geosynchronous satellite and Earth spin."

JAXA’s more advanced SPS concept solves the solar collection problem by employing two huge reflective mirrors positioned so that between the two of them, they would direct light onto two PV panels 24 hours a day.

"The two mirrors would be free flying, not tethered to the solar panels or the separate transmission unit, which means that we would have to master a sophisticated kind of formation flying to implement this system," Sasaki adds.

"Space agencies have some experience with formation flying, most notably in the docking maneuvers performed at the International Space Station, but coordinating a formation flight involving kilometer-scale structures is a big step from today’s docking procedures."

JAXA researchers are focusing on wireless power transmission, which can only be accomplished through laser or microwave beam, according to Sasaki.

While lasers, which have short wavelengths, are ideal for satellites due to the fact that they can be transmitted and received by relatively small components, their short-wavelengths can be blocked by the atmosphere and water molecules.

"No one wants a space-based solar power system that works only when the sky is clear," Sasaki points out.

Microwaves, on the other hand, have 80% efficiency and can penetrate the atmosphere.

"It would be difficult and expensive, but the payoff would be immense, and not just in economic terms," Sasaki writes. "If humanity truly embraces space-based solar power, a ring of satellites in orbit could provide nearly unlimited energy, ending the biggest conflicts over Earth’s energy resources.