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[Text/Observer Network Yan Shanshan] According to the Hong Kong English media "South China Morning Post" on July 14, Chinese scientists recently proposed a design plan to establish a communication and navigation constellation similar to the Beidou navigation system that can serve the entire lunar surface.

The report cited a paper titled "Near-Moon Space Constellation Orbit Design Method" published in "China Space Science and Technology" in June to introduce the research progress. The authors of the paper are Chen Shiyu and Ni Yanshuo from the Beijing Space Vehicle Design Department and Peng Jing, chief designer of the Chang'e-8 probe system of the China Aerospace Science and Technology Corporation's Fifth Academy.

The Chinese research team took into account various indicators in three aspects: relay communications, lunar navigation, and constellation construction and maintenance costs, and proposed a near-moon space navigation constellation consisting of 21 satellites. The plan aims to provide long-term, high-precision navigation for mankind's long-term, high-density exploration activities on the moon in a sustainable and cost-effective manner.

The South China Morning Post mentioned that although the paper did not give a specific construction timetable, the preliminary plan for China's lunar exploration project and the plan for the international lunar research station have been announced: China plans to send astronauts to the moon before 2030, and to build an international lunar research station with basically complete functions and basic supporting elements with the South Pole of the moon as the core before 2035, and to build an expanded version before 2045.

Screenshot of the paper

According to the paper, the lunar South Pole has a very small elevation angle to the Earth and is easily blocked by lunar craters, making it difficult to ensure a direct ground-based telemetry and control communication link. The back of the moon is blocked by the moon, so it is also impossible to achieve telemetry and control communication through the ground-based telemetry and control system. Therefore, it is necessary to deploy relay satellites in the near-moon space, including the Earth-Moon L1 and L2 libration points, to assist the lunar South Pole and back-to-ground telemetry and control communication.

The Earth-Moon Lagrange point, the Queqiao-1 relay satellite is in the halo orbit of the L2 point, while the Queqiao-2 is in the lunar orbit.

"The near-moon space navigation constellation can provide real-time, high-precision navigation and positioning for tasks such as lunar surface movement, landing and takeoff. It is the necessary basic guarantee to support human long-term, high-density exploration activities on the moon," the article wrote.

When reviewing the research plan of the paper, the South China Morning Post mentioned that global navigation satellite systems are currently being widely used on the surface of the earth or in near-Earth space. For example, the United States' Global Positioning System (GPS) and China's Beidou Satellite Navigation System (BDS) are both widely used, providing users with all-weather, high-precision positioning, navigation and other services.

According to the report, the global navigation satellite system is usually composed of 20-35 satellites, with an accuracy of several meters. Users can use the combination of signals from at least four satellites to locate and obtain time information. The lunar navigation scheme of the research team of the Beijing Space Vehicle General Design Department is similar to this, requiring at least four satellites to be visible to the target at the same time during navigation.

On June 25, 2024, the Chang'e-6 returner landed accurately in the designated area of ​​Siziwang Banner, Inner Mongolia, and worked normally, achieving the world's first sampling return from the far side of the moon. Visual China

The study proposes a near-moon space constellation construction route, which will gradually achieve 100% quadruple coverage of the entire moon in three stages (quadruple coverage refers to the proportion of time when at least four stars in the constellation are visible to the target at the same time). The three stages are as follows:

In the first stage, two elliptical frozen orbit satellites will be deployed to provide full-time ground relay communications for the lunar South Pole, achieving 100% single-layer coverage of the lunar South Pole; In the second stage, six elliptical frozen orbit satellites, two near-linear halo orbit satellites, and one L2 halo orbit satellite will be deployed to provide full-time navigation and positioning for the lunar South Pole, while achieving 100% single-layer coverage of the lunar polar region and the far side of the moon, allowing probes or humans at any location on the moon to communicate with the ground full-time; In the third stage, four elliptical frozen orbit satellites, two near-linear halo orbit satellites, one L1 halo orbit satellite, and three long-distance retrograde orbit satellites will be deployed to achieve 100% quadruple coverage of the entire moon, providing full-time navigation and positioning for probes or humans at any location on the moon.

The research team stated that in subsequent studies, they will combine orbital parameter optimization technology to form a more systematic near-moon space constellation optimization method, and globally optimize discrete variables such as orbital type and continuous variables such as orbital parameters to obtain the theoretically optimal constellation configuration.

In recent years, the construction of near-moon space constellations has become a hot topic in aerospace research. China launched the Queqiao-1 and Queqiao-2 relay satellites in 2018 and 2024, respectively, to provide relay communication support for multiple lunar exploration missions.

According to the WeChat public account "China's Spaceflight", the Queqiao-2 relay satellite uses a large elliptical frozen orbit around the moon as its mission orbit. Due to the irregular shape of the moon, spacecraft flying close to the moon are affected by the moon's gravity and other factors, and the flight orbit is prone to deviation. The large elliptical frozen orbit around the moon is a stable orbit around the moon. When a spacecraft flies in this orbit, the deviation of the flight orbit can be minimized.

On March 20, 2024, in Wenchang, Hainan, the Long March 8 Y3 carrier rocket carrying the Queqiao-2 relay satellite of the fourth phase of the lunar exploration project ignited and took off at the Wenchang Space Launch Center. Visual China

At the same time, the United States, Europe and Japan have also proposed plans to build lunar communication and navigation constellations.

In 2020, the National Aeronautics and Space Administration (NASA) proposed the "Lunar Network" (LunaNet) architecture to support the "Artemis" plan. It is used to meet the communication needs of lunar South Pole exploration and lunar back side exploration in the short term. Relay communication services are provided by 2-3 relay satellites in elliptical frozen orbits and the Gateway space station in a near-linear halo orbit.

On November 16, 2022, local time, in Florida, the United States, the Artemis 1 Space Launch System rocket, together with the Orion space capsule, was launched at NASA's Kennedy Space Center in Cape Canaveral. The Artemis 1 mission will launch an unmanned spacecraft to fly around the moon to test the spacecraft's propulsion, navigation and power systems in preparation for subsequent manned missions on the lunar surface. Visual China

Europe is also fully promoting the lunar communication service plan. In 2021, the European Space Agency (ESA) released the "Moonlight" plan, proposing to build a sustainable lunar shared communication and navigation system (LCNS) around 2027, and plans to launch the first "Lunar Pathfinder" satellite in 2025 to carry out technical verification in an elliptical frozen orbit.

In 2022, the Japan Aerospace Exploration Agency (JAXA) proposed the Lunar Navigation Satellite System (LNSS), planning to deploy eight satellites in an elliptical orbit to provide relay communications and navigation and positioning services for the lunar South Pole probe.

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