According to the Space Application Engineering and Technology Center of the Chinese Academy of Sciences, China's earth moon laser communication experiment task has made an important breakthrough, successfully establishing a two-way laser link at a distance of more than 400000 kilometers between the earth and the moon, and realizing two-way high-speed laser communication between the earth and the moon for the first time. This marks the official transition of China's space laser communication from near Earth orbit to the Earth Moon space.
Space laser communication is a communication method that uses lasers to transmit information, with advantages such as large bandwidth, fast speed, accurate direction, and good confidentiality. But the farther the distance, the greater the technological challenge. Yang Lei, a researcher at the Center for Space Application Engineering and Technology of the Chinese Academy of Sciences, said: "Deep space laser communication has been carrying three mountains: hundreds of thousands of kilometers away, it is extremely difficult to accurately align the beam; when the signal is transmitted to the ground, it is almost too weak to receive; and the transmission speed has not been improved."
The first difficulty lies in 'aiming'. The communication between the Earth and the Moon is like passing an extremely fine beam of light through a high-speed moving "pinhole" at a distance of 400000 kilometers. Even if there is an extremely small angular deviation at the transmitting end, there will be a positional error of several kilometers when reaching the vicinity of the target. To this end, the research team has come up with a new approach: taking into account various factors such as satellite orbit, telescope installation errors, atmospheric refraction, laser flight time, etc., to ensure that the satellites in the sky and the telescopes on the ground are always aligned during motion, ensuring that the laser can accurately illuminate the predetermined position.
The problem of "difficult aiming" has been solved, and a new one has emerged: by the time the laser reaches the ground after running 400000 kilometers, it has become so weak that only a few photons remain. The signals that ground-based telescopes can receive are pitifully limited, and moonlight, starlight, and city lights can also mix in and cause trouble. For this purpose, the team used an "ultra sensitive detector" capable of detecting individual photons and developed a complex signal recognition algorithm to extract effective signals from massive noise. It's like accurately hearing the sound of a needle hitting the ground in a bustling city thousands of miles away.
The signal can be received, but the transmission speed also needs to keep up. The team has significantly improved data processing efficiency through technological breakthroughs. This experiment has initially achieved a communication rate of 1.25Mbps (megabits per second) upstream and 100Mbps downstream. Yang Lei gave an example: "Taking an 8K high-definition image of the lunar surface as an example, it takes about 4 to 5 minutes to download it using a traditional 5Mbps microwave link; After switching to hundreds of Mbps laser communication, it only takes about 12 seconds. ”
At present, the 'information highway' between the Earth and the Moon has been established, and in the future we will obtain more and more original scientific data. Yang Lei said that related technologies will also provide new means of high-speed information transmission for China's manned lunar landing, lunar research station construction, and deep space exploration. (Outlook New Era)