Chinese Scientists Achieve Two-Way Lunar Laser Communication at 400,000 km

A team of Chinese scientists has completed a lunar laser communication test, verifying high-speed, two-way optical links in space, according to the China Academy of Sciences’ Space Utilization Technology and Engineering Center.

Extending China’s Deep-Space Optical Communications

The center stated in a statement carried by Xinhua News Agency on Saturday that, after more than one year of orbital testing, the team established a two-way laser communication link across a distance exceeding 400,000 kilometers. This marks an expansion of China’s space-based laser communications capability—from low Earth orbit into deep space.

Advantages and Technical Hurdles of Laser Links

Compared with conventional microwave communications, laser-based systems offer higher data rates, broader bandwidth, stronger security, and more compact, lightweight equipment. However, establishing laser communication across the Earth–Moon distance requires overcoming three primary challenges: laser beam alignment, signal attenuation, and data transmission speed.

“Threading a Needle from a Thousand Miles Away”

Yang Li, a researcher at the center and head of the laser communication test team, described Earth–Moon communication as “threading a needle from a thousand miles away.” Due to the vast separation, even minor satellite vibrations or atmospheric disturbances on Earth can deflect the laser beam. An angular deviation of just a fraction of a degree may result in a targeting error of several kilometers upon reaching the Moon, the center explained.

Innovative Acquisition and Tracking Scheme

The team developed an innovative acquisition and tracking scheme integrating corrections for orbital delay, atmospheric interference, and optical signal dispersion. This enables both ground-based and spaceborne equipment to maintain precise alignment while in motion.

Detecting Single Photons Amidst Noise

After traveling 400,000 kilometers back to Earth, the laser signal becomes extremely weak—ground-based telescopes detect only a few photons per reception cycle. Additional noise sources include moonlight, starlight, and urban lighting. The center likened this challenge to “hearing a pin drop in a crowded market.” To address it, researchers developed high-speed single-photon detection technology using superconducting devices, alongside highly sensitive algorithms to extract valid communication signals from background noise.

High-Bandwidth Signal Processing and Coding

To overcome data-rate limitations, the team implemented high-bandwidth signal processing techniques and adopted specialized coding schemes designed to counter noise. The test achieved two-way communication rates of 1.25 megabits per second for the uplink and 100 megabits per second for the downlink.

Supporting Future Lunar Missions

The center noted that as crewed lunar landings and the establishment of a lunar research station approach, future lunar exploration missions will generate massive volumes of observational imagery and scientific data—volumes beyond the capacity of traditional radio-frequency communication bandwidth. The Earth–Moon “information superhighway” enabled by laser communications will provide a new, high-speed data transmission pathway for upcoming lunar missions.