Image Caption:
Diagram of the Queqiao-2 relay satellite. Image courtesy of China National Space Administration.
Queqiao-2 Relay Satellite Diagram. Courtesy of the China National Space Administration
At 8:31 AM on March 20th, the Queqiao-2 relay satellite successfully lifted off, commencing its journey to the Moon. As China's second dedicated relay satellite beyond Earth's orbit, Queqiao-2 will serve as a new communication bridge between the Earth and the Moon for the ongoing Chang'e-4 mission and the upcoming Chang'e-6, Chang'e-7, and Chang'e-8 lunar exploration missions of the fourth phase of China's lunar program.
On March 20th at 8:31 AM, the Queqiao-2 relay satellite was successfully launched into space by the Long March 8 Y3 carrier rocket from the Wenchang Space Launch Center in China. Queqiao-2, a "key component" of the subsequent missions of the fourth phase of the lunar program, will establish a new "Magpie Bridge" between the Earth and the Moon, providing relay communication for missions such as Chang'e-4 and Chang'e-6.
After 24 minutes of flight, the Long March 8 Y3 carrier rocket and satellite separated, sending Queqiao-2 directly into its intended lunar transfer orbit with a perigee altitude of 200 kilometers and an apogee altitude of 420,000 kilometers. The satellite's solar panels and relay communication antennas were subsequently deployed normally, marking the complete success of the launch mission.
How is this new "Magpie Bridge" different, and what role will it play in the future? How will the后续 of the fourth phase of the lunar program unfold?
Enhanced Earth-Moon Communication Capabilities and Performance
"As a 'key component' of the implementation of the fourth phase of the lunar program, the Queqiao-2 relay satellite will serve as a communication hub," said Ge Ping, deputy director of the China National Space Administration's Lunar and Space Engineering Center. He added, "The successful launch of Queqiao-2 has realized on-time launch, precise orbit insertion, and precise control, laying a solid foundation for the subsequent execution of a series of flight control tasks."
Why was the Queqiao-2 relay satellite launched?
Experts explained that, as the Moon always presents one side towards the Earth, rovers that land on the lunar far side are blocked by the Moon itself and are unable to directly establish telemetry, tracking, and command communication or data transmission with Earth. Thus, a relay satellite is needed to bridge the information gap between ground stations and lunar rovers. The name "Magpie Bridge" is derived from an ancient Chinese folktale, both reflecting China's cultural heritage and vividly explaining the satellite's unique role.
In 2018, China launched the first relay satellite, also named "Magpie Bridge," to provide relay communication for the Chang'e-4 rover that landed on the lunar far side. The original Magpie Bridge relay satellite has been in orbit for several years and has exceeded its intended service life.
"The landing and sampling sites for the fourth phase of the lunar program are mainly located in the Moon's south polar region and the lunar far side," said Ge Ping. "Therefore, a relay satellite with enhanced capabilities and performance is needed to establish a new 'relay communication station' between the Moon and the Earth, solving the communication and data transmission issues between the lunar far side rover and the Earth."
In response to the requirements of the fourth phase of the lunar program, researchers have made breakthroughs in the design of the Queqiao-2 relay satellite. Compared to the original Magpie Bridge relay satellite, the Queqiao-2 relay satellite incorporates more technological innovations, has a greater range of technical capabilities, provides more functions, features more complex interfaces, presents greater manufacturing challenges, and extends the mission timeline. Moreover, beyond its relay communication role, Queqiao-2 also carries multiple scientific payloads for scientific exploration.
Apart from supporting the fourth phase of China's lunar program, the Queqiao-2 relay satellite will also provide relay communication services for domestic and international lunar exploration endeavors.
Long March 8 Carrier Rocket's Maiden "Lunar Journey"
The Long March 8 carrier rocket used to launch this mission is a new generation of medium-sized, two-stage, liquid-propellant,捆绑式运载火箭, filling the gap in China's 3-5 ton Sun-synchronous orbit launch capability. Notably, this launch marked the Long March 8 carrier rocket's maiden voyage to the lunar transfer orbit.
The research and development team tailored the rocket's design to meet the mission requirements, such as multiple windows, multiple trajectories, and low-altitude, high-speed flight profiles.
"For this Queqiao-2 relay satellite mission, we've customized three capabilities: a more refined trajectory design, a more flexible active yaw technology, and more reliable thermal protection measures," said a representative from the rocket's research and development team.
Experts explained that, as a lunar satellite, the Queqiao-2 relay satellite has a narrow launch window known as the "lunar window," which occurs for only a few days each month. The rocket's research and development team designed six trajectories spread across three consecutive days, with two trajectories per day, starting from the first window. This ensures that the satellite can successfully depart and arrive safely under various conditions.
To address the impact of high-altitude wind on the rocket's launch, the research and development team not only incorporated mature methods such as autonomous anti-interference control technology but also added an automatic yaw reduction technique to the Long March 8 carrier rocket. This enables the rocket to present a more stable surface to the high-altitude wind and counteract its effects through self-rotation.
Compared to the Sun-synchronous orbit missions that the Long March 8 carrier rocket typically performs, the lunar transfer orbit has a lower orbit insertion altitude and a higher rocket flight speed. As the rocket rapidly traverses the atmosphere, the friction between the rocket body and the atmosphere generates higher temperatures, with the tip and nose cone bearing the brunt of these extreme conditions. In response, the rocket's research and development team applied an additional layer of thermal protective coating to the rocket's exterior and increased the thickness of critical areas, enhancing its ability to withstand the harsh conditions of the lunar transfer orbit.
Chang'e-6 to Launch in the First Half of the Year
"A successful launch is only the first step," explained Ge Ping. "The Queqiao-2 relay satellite still needs to perform a series of critical maneuvers, such as orbital mid-course correction and near-Moon braking." He added, "After Queqiao-2 adjusts to a 24-hour elliptical frozen lunar orbit, it will conduct in-orbit communication tests with Chang'e-4 and Earth-to-space communication tests with Chang'e-6 to verify their coordination and compatibility during joint Earth-Moon operations and to determine whether Queqiao-2 has the capability to support Chang'e-6's lunar far side sample return mission."
Chang'e-6 is scheduled to launch in the first half of this year. Experts explained that all ten lunar sample return missions conducted to date have taken place on the lunar near side, while the lunar far side is generally more ancient than the near side and hosts one of the Moon's three largest impact basins, the Aitken Basin, which holds significant scientific value. Chang'e-6 has selected a landing site in the lunar far side's South Pole-Aitken Basin to collect and return samples from different regions and ages, deepening our understanding of the Moon's formation and evolutionary history through systematic and long-term laboratory research on the returned lunar far side samples. 探月合作
全球掀起探月热潮，各国纷纷开展探月计划。中国探月工程一直重视国际合作，欢迎各界参与。以往的探月任务已有多次国际合作成功案例。中国已对嫦娥五号月岩样品开放国际申请，未来的探月四期和行星探测计划也将公开征集合作方案。
嫦娥六号国际载荷
嫦娥六号任务搭载了法国的氡探测器、欧空局的负离子探测器、意大利的激光角反射镜和巴基斯坦的立方星等四项国际载荷。
国际月球科研站计划
中国正在推进国际月球科研站大科学工程，希望吸引更多国际合作伙伴。该计划旨在拓展人类对月球的认知，促进和平利用太空，构建人类命运共同体。
探月四期任务
探月四期工程获批于2021年12月，包含嫦娥四号、六号、七号和八号共四次任务。嫦娥四号已于2018年实现月球背面软着陆，嫦娥六号将于今年上半年发射，嫦娥七号和八号将共同构建月球科研站基础设施，进行月球环境探测等任务。
