Recently, the Technology and Engineering Center for Space Utilization of the Chinese Academy of Sciences (CAS) announced a significant breakthrough in China's lunar laser communication test mission. Following over a year of on-orbit testing, the research team successfully established a two-way laser link over a distance exceeding 400,000 kilometers, achieving the nation's first two-way high-speed lunar laser communication. This milestone officially marks China's transition from near-Earth orbit to cislunar space in laser communication.
Implemented via the Distant Retrograde Orbit-A (DRO-A) satellite, the test preliminarily achieved an uplink speed of 1.25 Mbps and a downlink speed of 100 Mbps. Compared to traditional microwave communication, space laser communication boasts significant advantages, including large bandwidth, high speed, precise directionality, strong security, and compact, lightweight equipment. However, over the vast cislunar distance of hundreds of thousands of kilometers, deep-space laser communication has long faced "three major mountains": extreme difficulty in precise beam alignment, severe signal attenuation during transmission, and the challenge of boosting transmission rates.
To solve the "aiming" challenge, the research team innovatively proposed a two-way acquisition and tracking scheme tailored for ultra-long distances and extremely weak signal conditions. By comprehensively factoring in satellite orbits, telescope installation errors, atmospheric refraction, and laser flight time, they successfully ensured that the satellite and ground telescope maintained precise alignment during high-speed movement. This is akin to threading a high-speed moving "needle hole" with an extremely thin beam of light from 400,000 kilometers away.
To address the issue of weak signals, laser beams arriving at the ground after traveling 400,000 kilometers are attenuated to just a few photons. To overcome this, researchers utilized "ultra-sensitive detectors" (superconducting nanowire single-photon detector arrays) capable of detecting individual photons, alongside complex signal recognition algorithms and picosecond-level time identification technology. This is equivalent to assigning a super-precise "timestamp" to each photon, extracting valid signals from massive background noise-a feat comparable to accurately hearing a needle drop in a bustling city thousands of kilometers away.
Regarding transmission rates, the team broke through high-bandwidth communication processing technologies, significantly enhancing data processing efficiency. For instance, transmitting an 8K high-definition lunar surface image via a traditional 5 Mbps microwave link takes about 4 to 5 minutes, whereas the 100 Mbps laser communication reduces this time to merely 12 seconds, representing a speed increase of dozens of times.
Led by the CAS Technology and Engineering Center for Space Utilization, this mission was jointly implemented with the Zhejiang Lab, the Yunnan Observatories of CAS, and the Shanghai Institute of Microsystem and Information Technology of CAS. This technological breakthrough officially propels China's space laser communication into cislunar space, establishing a lightweight, compact, low-power, and high-speed information transmission capability. This milestone will not only eliminate the bottleneck of data transmission in deep space exploration but also provide crucial high-speed information transmission methods and vital technical support for China's future crewed lunar landings, the construction of an international lunar research station, and deep space exploration missions to Mars and beyond.
