Researchers have completed an Earth-Moon two-way laser communication link test, successfully transmitting high-speed data across a distance exceeding 400,000 kilometers after more than a year of in-orbit testing. Announced by the Chinese Academy of Sciences, the breakthrough establishes a high-speed information highway for upcoming lunar exploration and crewed missions.
Space communication has long relied on traditional microwave signals, but the demands of future lunar research stations and crewed landings require a massive leap in data capacity. Traditional bandwidth can no longer support the high-volume observation images and complex scientific measurements expected from deep-space missions. To solve this bottleneck, researchers at the Technology and Engineering Center for Space Utilization (CSU) of the Chinese Academy of Sciences spent more than a year conducting in-orbit trials to build a deep-space optical link.
The resulting Earth-Moon laser communication link spans a distance of over 400,000 km, marking a shift from near-Earth orbit into deep space. Compared to conventional microwave networks, laser communications deliver faster transmission speeds, broader bandwidth, enhanced security, and more compact hardware.
Overcoming Deep-Space Hurdles: Beam Alignment and Photon Detection
Establishing an optical connection across lunar distances presents physical obstacles. According to Yang Lei, a researcher at the CSU and head of the laser communication test team, Earth-Moon communication is like threading a needle from a thousand miles away.
At 400,000 kilometers, even minor satellite wobbles or ground atmospheric turbulence can throw a laser beam off course. A tiny angular deviation at the transmission point results in a kilometer-scale miss by the time the light reaches the Moon. To counter this, the team engineered a specialized acquisition and tracking scheme. This system integrates corrections for orbital, atmospheric, and optical propagation delays, keeping spaceborne and ground equipment aligned while in motion.
Signal degradation posed an equally severe test. After traveling the distance back to Earth, the incoming laser beam attenuates so drastically that ground telescopes capture only a few photons at any given moment. Urban lighting, moonlight, and starlight create interference. The CSU likened the challenge to hearing the sound of a falling pin in a bustling market.
Researchers overcame this background interference by deploying high-speed superconducting single-photon detection technology paired with high-sensitivity extraction algorithms.
Gigabit Speeds and the Atmospheric Challenge
The successful test achieved two-way communication rates of 1.25 Mbps on the uplink and 100 Mbps on the downlink. This performance builds on rapid advancements in optical downlinks developed across recent orbital tests. In geostationary orbit experiments, researchers previously demonstrated a 1Gbps laser downlink from 36,000km above Earth using a 2-watt transmitter.
That geostationary experiment, detailed in Acta Optica Sinica by teams led by Wu Jian of Peking University of Posts and Telecommunications and Liu Chao of the Chinese Academy of Sciences, tackled the atmospheric distortion that occurs during the final leg of a space-to-ground transmission. Rather than letting shifting air scatter the beam, the ground system at the Lijiang Observatory utilized a 1.8-metre telescope equipped with 357 micro-mirrors.
By combining adaptive optics with a multi-plane light converter—a technique termed AO-MDR synergy—the system split the disrupted wavefront into eight base-mode channels, selecting and combining the three strongest paths. This approach boosted the proportion of usable signal from 72 per cent to 91.1 per cent, proving that high-speed laser links can maintain operational reliability even when forced to cut through turbulent air.
Preparing for Manned Lunar Missions
As space agencies look toward crewed lunar landings and the establishment of lunar research stations, the volume of observation images and scientific data will increase.
The successful integration of deep-space optical links ensures that massive volumes of data can be transmitted. As the CSU noted, this newly validated Earth-Moon laser information highway
provides a new high-speed data transmission route for upcoming lunar missions.
