Space Solar Power Station StarBeam Completes First Microwave Power Transmission: 50kW Delivered from 36,000km Orbit

Space Solar Power Station StarBeam Completes First Microwave Power Transmission

On October 1, 2028, JAXA and Mitsubishi Heavy Industries jointly announced that the space solar power station StarBeam successfully completed its first large-scale microwave power transmission experiment from geostationary orbit (36,000km altitude). The experiment transmitted 50 kilowatts of solar power via microwave beam to a ground receiving station, achieving end-to-end transmission efficiency of 23%.

StarBeam's core technology deploys large-area solar collection arrays in space, converting solar energy into microwave beams for directed transmission to ground receiving stations (rectennas) that convert microwaves to DC power. Space solar power's advantage is immunity to weather and daylight cycles — at geostationary orbit, solar energy utilization is 5 to 10 times that of ground-based systems.

JAXA StarBeam project director Professor Susumu Sasaki stated that this experiment marks humanity's first meaningful-scale power transmission from space to ground. While 50 kilowatts only serves a few dozen households, it proves the technical feasibility. The next step is scaling to megawatt levels.

StarBeam's space array, designed and built by Mitsubishi Heavy Industries, covers 200 square meters with 3,600 high-efficiency gallium arsenide solar cells. Solar-generated DC power is converted to 2.45GHz microwave beams via magnetron arrays and transmitted through a 26-meter diameter antenna. The ground receiving station is located at Tanegashima in Kagoshima Prefecture, with a 4,000-square-meter rectenna.

The 23% transmission efficiency has sparked industry discussion. This means for every kilowatt-hour generated in space, only 0.23 kWh reaches the ground. In comparison, ground solar plus lithium battery storage systems achieve about 85% overall efficiency. However, JAXA notes that space solar generates 5 to 10 times more power per unit area, and considering annual energy output per unit area, space solar remains competitive.

Cost is the biggest challenge. StarBeam's current construction and launch costs are approximately $200,000 per kilowatt — 100 times that of ground solar. Mitsubishi Heavy Industries says using SpaceX's Starship heavy-lift rocket and modular space assembly technology, costs could drop to $5,000 per kilowatt by 2035, when space solar would become economically viable in specific scenarios like islands and polar regions.

Safety concerns about microwave beam radiation have been raised by the public. JAXA emphasizes StarBeam's microwave beam power density is controlled at 1 milliwatt per square centimeter, far below ICNIRP safety limits. The beam center's power density is approximately one-thousandth of a household microwave oven.

China is pursuing similar projects. CASC's Solar Chase Project plans to launch a megawatt-class space solar verification station before 2030. The EU, US, and India also have space solar programs, with commercial competition expected in the 2030s.