China to build a lunar communications and navigation constellation
HELSINKI — China plans to set up a constellation around the moon to provide communication and navigation services for future operations on the lunar surface.
China will take the lead in demonstrating a small, lunar relay communication and navigation system, Wu Yanhua, deputy director of the China National Space Administration (CNSA), told Chinese media on April 24.
The first launch for the small constellation could take place in 2023 or 2024, according to Wu, who added that countries around the world are welcome to jointly build it.
No further details were provided, but China’s lunar exploration roadmap and mission concepts provide insight into the plans.
The most immediate use of the communications relay and navigation services would be to support the Chang’e-6 sample return mission and Chang’e-7, which includes an orbiter, lander, rover and a small hopping spacecraft for investigating shadowed craters for water-ice.
Wu stated at a national space day ceremony that Chang’e-6 could launch in 2024 or 2025. Chang’e-7 has previously been stated to be scheduled for launch around the same timeframe and possibly ahead of Chang’e-6.
Both Chang’e-6 and Chang’e-7 are expected to target landings in the vicinity of the lunar south pole. While China has a relay satellite stationed in a halo orbit around Earth-moon Lagrange point 2 to facilitate communications with the Chang’e-4 lander and Yutu-2 rover on the lunar far side, a different orbit would be needed to enhance communications and facilitate sending larger volumes of data between Earth and the lunar south pole.
Chang’e-8, designed for in-situ resource utilization and 3D-printing technology tests, will follow as a stepping stone towards the International Lunar Research Station (ILRS) with cooperation with Russia.
The ILRS project would see the construction of a permanent, robotic facility on the moon across 2030-2035. The base would, once completed, be capable of hosting long term human stays.
NASA, the European Space Agency and private firms are also planning lunar communication and navigation infrastructure to support the Artemis lunar exploration program. The Artemis and ILRS projects are seen by some as initial developments of an emerging cis-lunar economy.
China’s lunar communications and navigation constellation is likely to be built incrementally, providing increasing capabilities as its lunar plans progress.
One concept for a relay satellite to support Chang’e-7 would use an inclined highly elliptical frozen orbit, with a perilune of 300 kilometers and apolune of 8,600 kilometers and an inclination of 54.8 degrees. This would allow communication links between Earth and the lunar south pole for over 8 hours during its roughly 12-hour period orbit.
Adding additional satellites in similar orbits would provide constant communications and navigation coverage, similar to how multiple satellites in Molniya orbits are used for high latitudes on Earth.
Other possibilities are being considered, however. Kristin Burke, a researcher at the China Aerospace Studies Institute (CASI), told SpaceNews that Chang’e-5 extended mission activities could be used to test out new orbits for a constellation.
Chang’e-5, after delivering fresh lunar samples to Earth in late 2020, headed to Sun-Earth Lagrange point 1 before returning to the Earth-moon system later in 2021. The orbiter is currently in distant retrograde orbit (DRO) of the moon, according to amateur satellite trackers.
“China’s Chang’e-5 orbiter is supporting a few different follow on exploration missions, to include future solar science probes and now possibly future spacecraft at lunar Distant Retrograde Orbit,” Burke said.
“Chinese academics’ English and Mandarin language articles indicate that China is considering a couple different orbital regime combinations for a communications and navigation architecture. Some of those include satellites in DRO,” says Burke.
The first relay satellite could launch on a dedicated launcher or as part of the Chang’e-7 spacecraft stack. The relay satellite is likely to be a first step to facilitate new, more complex activities at the lunar south pole as part of China’s long term lunar exploration plans.