China Establishes Three-Satellite Network in Earth-Moon Orbit

This image provided by the Technology and Engineering Center for Space Utilization (CSU) of the Chinese Academy of Sciences (CAS) illustrates the three-satellite constellation based on the Distant Retrograde Orbit (DRO) in the Earth-moon region of space. (Technology and Engineering Center for Space Utilization of the Chinese Academy of Sciences/Handout via Xinhua)

China has successfully established the world’s first three-satellite constellation utilizing Distant Retrograde Orbit (DRO) within the Earth-moon space, marking a major step forward in space exploration, utilization, and preparation for future manned deep-space missions.

Developed by the Chinese Academy of Sciences (CAS), satellites DRO-A and DRO-B have now formed inter-satellite measurement and communication links with DRO-L, an earlier satellite launched into near-Earth orbit. This accomplishment was announced at a symposium on DRO exploration in Earth-moon space, held Tuesday in Beijing.

DRO is a distinctive orbit that lies within the Earth-moon region, which stretches up to 2 million kilometers from Earth. According to Wang Wenbin, a researcher at the CAS Technology and Engineering Center for Space Utilization (CSU), this orbit moves in a prograde path around Earth and a retrograde path around the Moon. Its stability and low fuel requirements make it an ideal location for supporting scientific exploration, space infrastructure, and crewed missions deeper into space.

The experimental satellite DRO-L was launched into a sun-synchronous orbit on February 3, 2024, and has since been conducting scheduled experiments. Meanwhile, the DRO-A and DRO-B satellites were launched on March 13, 2024, from the Xichang Satellite Launch Center in Sichuan Province. Although an anomaly in the rocket's upper stage initially prevented them from reaching their designated orbit, the mission ultimately achieved its key goals.

In response to the challenge, the satellite team carried out a critical "life-or-death" rescue mission under extreme conditions, swiftly executing several emergency orbital maneuvers to adjust the trajectory of the two satellites.

Following a journey of 8.5 million kilometers, the DRO-A/B satellite pair successfully reached their intended orbit, according to Zhang Hao, a researcher at the Technology and Engineering Center for Space Utilization (CSU) who took part in the recovery effort.

The two satellites were separated on August 28, 2024. Subsequently, both DRO-A and DRO-B established K-band microwave links with the earlier satellite DRO-L, enabling inter-satellite measurement and communication and successfully testing the networking capabilities of the three-satellite constellation, Zhang added.

At present, DRO-A remains in Distant Retrograde Orbit, while DRO-B operates within maneuvering orbits in the Earth-moon space, CSU confirmed.

This mission demonstrated China’s significant advancements in autonomous navigation and fault recovery in deep space. The success showcased the satellite team's agility in handling complex scenarios and set the stage for more cost-effective deep-space missions, said Zhang Jun, a senior engineer at the CAS Innovation Academy for Microsatellites.

Wang Qiang, CSU’s deputy director, noted that after the constellation was successfully networked, a series of advanced scientific and technological experiments were launched, further propelling Earth-moon space research.

In 2017, researchers at the Technology and Engineering Center for Space Utilization (CSU) began studying Distant Retrograde Orbits (DRO) in the Earth-moon region, overcoming major technical hurdles and introducing the idea of a DRO-based spaceport. By February 2022, the Chinese Academy of Sciences (CAS) launched a project to develop a three-satellite constellation in Earth-moon space based on DRO.

The initiative achieved a global first by enabling spacecraft to enter DRO with minimal fuel consumption. Through a highly efficient design, the team completed a lunar transfer and DRO insertion using only one-fifth of the typical fuel requirements. This innovation dramatically lowered the cost of accessing Earth-moon space and laid the groundwork for large-scale exploration, explained Zhang Jun.

The project also successfully tested K-band microwave communication and measurement links between the satellites and Earth across a distance of 1.17 million kilometers, marking a major technological milestone for constructing large-scale constellations in Earth-moon space, Zhang noted.

To address issues such as limited precision in ground-based tracking, high costs, and low efficiency in lunar and deep-space missions, the team developed a space-based, satellite-to-satellite orbit determination system.

By analyzing just three hours of inter-satellite measurement data, the team achieved orbit determination accuracy levels that would normally require two days of ground-based tracking. This breakthrough significantly cut operational costs and boosted the overall efficiency of spacecraft navigating the Earth-moon region, Zhang added.

Looking ahead, the research team plans to further explore the intricate and varied orbits within the Earth-moon space and examine the characteristics of the lunar space environment. According to Wang, scientists aim to utilize the long-term stability of Distant Retrograde Orbit (DRO) to conduct foundational scientific studies in areas such as quantum mechanics and atomic physics.