Chinese researchers complete Earth-Moon two-way laser link test

Researchers in China have completed an in-orbit Earth-Moon laser communications test, achieving two-way high-speed link capabilities across a distance exceeding 400,000 kilometers after more than a year of testing. The milestone overcomes major technical challenges in beam alignment and signal weakness, paving the way for high-speed data transmission on upcoming lunar missions.

Chinese Academy of Sciences Technology and Engineering Center for Space Utilization

Chinese researchers have successfully established a two-way laser communication link between Earth and the Moon across a distance of more than 400,000 km. The Technology and Engineering Center for Space Utilization (CSU) of the Chinese Academy of Sciences announced the milestone on Friday, August 29, following more than a year of in-orbit testing, marking an expansion of the country’s space laser communications from near-Earth orbit into deep space.

Overcoming Distance, Atmospheric Turbulence, and Extreme Signal Weakness

Compared with traditional microwave communications, laser communications offer faster speeds, greater bandwidth, stronger security, and more compact hardware. However, building an optical link across lunar distances required researchers to solve three formidable technical hurdles: beam alignment, signal weakness, and transmission speed.

Earth-Moon communication is like threading a needle from a thousand miles away, said Yang Lei, a researcher at the CSU and head of the laser communication test team.

At lunar distances, tiny satellite wobbles or ground atmospheric turbulence can cause laser beams to drift, resulting in a kilometer-scale miss from a tiny angular deviation. To maintain contact, the team developed an innovative acquisition and tracking scheme that integrates corrections for orbital, atmospheric, and optical propagation delays, enabling ground and spaceborne equipment to maintain precise alignment while in motion.

Once the laser signal traveled 400,000 km back to Earth, it arrived so faint that ground telescopes received only a few photons at a time. Natural interference from moonlight, starlight, and urban lighting compounded the difficulty—akin to hearing the sound of a falling pin in a bustling market, the CSU said. Researchers developed high-speed superconducting single-photon detection technology and high-sensitivity algorithms to extract valid communication signals from background noise. To tackle the speed bottleneck, the team developed high-bandwidth signal processing technology and adopted special coding schemes to counter noise.

Gigabit-Class Performance and Ground-Station Engineering

Lijiang Observatory

The work, published in Acta Optica Sinica, was led by Wu Jian of Peking University of Posts and Telecommunications and Liu Chao of the Chinese Academy of Sciences. By combining adaptive optics with a multi-plane light converter that split signals into eight base-mode channels—from which the receiver selected the three strongest channels and combined them for decoding—the ground station successfully recovered clean data from a 2-watt laser downlink originating from a geostationary satellite parked about 36,000 km above Earth. That methodology, described as AO-MDR synergy, boosted the proportion of usable signal from 72 per cent to 91.1 per cent.

Building on these hardware and algorithmic advances, the deep-space Earth-Moon test achieved two-way communication rates of 1.25 Mbps uplink and 100 Mbps downlink.

Preparing an Information Highway for Future Lunar Missions

Acta Optica Sinica

With manned lunar landings and lunar research station construction on the horizon, future lunar exploration will generate massive volumes of observation images and scientific data that traditional communications bandwidth can no longer support.