Japan’s OHISAMA demonstration satellite is scheduled to be launched in fiscal 2026 on a mission that could revolutionize clean energy.
Although earlier experiments have detected signals transmitted from orbit, the OHISAMA project aims to be the first in the world to deliver solar power to a receiving site on Earth and convert it into usable electricity.
The satellite will be carried aboard Space One Co.’s Kairos 5 small rocket.
BYPASSING WEATHER OBSTACLES
Space-based solar power (SBSP) refers to the concept of placing large solar collectors in orbit that can convert sunlight into electricity onboard. That energy is transmitted wirelessly, typically by microwave or in some concepts by laser, to a receiving station on Earth.
The received energy is then converted back into electricity for distribution through the grid.
SBSP remains an experimental technology and is positioned as a long-term research and development target under the Japanese government’s Basic Energy Plan.
Unlike ground-based solar and wind power, SBSP is largely insulated from weather-related variables and the day-night cycle.
In addition, the ability to modulate transmission output and redirect power to different locations could make SBSP a flexible option during disasters and periods of fluctuating demand.
A model proposed by Japan Space Systems (J-spacesystems), a nonprofit R&D foundation commissioned by the Ministry of Economy, Trade, and Industry to develop the system, envisions an architecture featuring 2.5-kilometer-square solar arrays deployed in geostationary orbit about 36,000 kilometers above Earth.
Electricity generated in orbit would be transmitted by microwave to a ground-based receiving antenna roughly 4 kilometers in diameter and then fed into the power grid.
Under this model, a single SBSP unit would generate about 1 gigawatt, an output described as sufficient to cover more than 10 percent of Tokyo’s annual electricity consumption.
MICROWAVES BEAMED FROM 450 KM ABOVE
According to J-spacesystems, the experiment will test whether power transmitted from space as microwaves can be efficiently converted back into electricity on the ground.
The OHISAMA satellite, weighing about 180 kg, carries an integrated power-generation and transmission panel measuring 70 cm by 2 meters.
Its generating capacity is a modest 720 watts, but the mission aims to use energy received by a 64-meter parabolic antenna at the Japan Aerospace Exploration Agency’s (JAXA) Usuda Deep Space Center in Nagano Prefecture to light an LED.
The Usuda facility is used to track and communicate with deep-space spacecraft.
Following a successful wireless power transmission test from an aircraft at an altitude of 7 km in 2024, the satellite mission will beam power from a 450-km orbit to assess how transmission distance, the ionosphere and the atmosphere affect efficiency.
JAPAN A LEADER IN SBSP RACE
A central challenge in SBSP wireless power delivery is limiting diffraction-driven beam spreading, which typically requires very large transmitting apertures and precise phase control.
Many SBSP concepts rely on retrodirective beam control: the ground-based rectenna sends a pilot signal that the satellite uses to steer the microwave beam back toward the receiver.
Japan has extensive R&D experience in microwave power transmission and retrodirective beam pointing.
According to J-spacesystems, SBSP development is accelerating in the United States, China and Europe, and the U.S. military is also widely believed to be pursuing its own experimental satellites.
First proposed in the United States in the 1960s, the SBSP concept holds that space-based systems could deliver as much as 10 times more energy per year than terrestrial solar because cloud cover and the day-night cycle constrain generation on Earth.
In Japan, SBSP research and development has been under way since the 1980s. Through ground-based trials and other tests, Japan has advanced the demonstration and validation of key component technologies, including high-precision beam control, integrated generation-and-transmission panels, and more efficient conversion of electrical power into microwaves.
“Technologically, Japan is leading the world in this field,” said Hiroki Yanagawa, a senior executive in J-spacesystems’ Satellite System and Earth Observation Division.
SBSP COULD POWER LUNAR EXPLORATION
In 2023, the California Institute of Technology launched an SBSP demonstrator and succeeded in short‑distance power transmission in space as well as in detecting faint microwave signals on the ground. But it did not deliver usable electricity at meaningful levels.
If electricity beamed from OHISAMA can be received, converted and used on the ground, it would represent a world first.
Such a success would likely be followed by additional in-orbit trials, with an eye toward commercialization in the 2040s. Potential longer-term applications include supplying power from orbit to support lunar exploration missions.
The launch schedule, however, remains contingent on the performance of Space One’s Kairos rocket.
After failures of the first two launches, attention has shifted to the flight of Kairos 3 on Feb. 25.
“While overseas rockets were an option, we selected Kairos in line with national policy to support Japan’s private-sector launch capabilities,” said Yanagawa of J-spacesystems.