HELSINKI — China has sent several small spacecraft into specialized lunar and cislunar orbits to test communications, navigation and orbital dynamics for planned Earth-moon infrastructure.
China’s DRO-A and B spacecraft, launched in March 2024 and rescued via a series of maneuvers following an upper stage failure, entered their intended lunar distant retrograde orbits (DRO) in August that year. Meanwhile, Tiandu-1—launched with the Queqiao-2 lunar relay satellite in 2024 ahead of the Chang’e-6 sample return mission—also reached lunar orbit.
DRO-B and Tiandu-1 have since been sent into specific Earth-moon resonance orbits, according to official updates and amateur tracking. DRO-B is in a 3:2 resonance orbit, meaning it completes three orbits around Earth in the time it takes the moon to complete two orbits around Earth, while Tiandu-1 is in a 3:1 resonance orbit.
The spacecraft and their orbits are being used to verify the key technologies and operations for China’s planned Queqiao constellation. The system aims to establish comprehensive communication, navigation and remote sensing to support cislunar activities, which includes establishing assets in various orbits and at Earth-moon Lagrange points. China has already utilized one of these points to facilitate lunar far side landing missions.
Tiandu-1 entered its own 3:1 resonance orbit May 22, according to a May 27 social media post by China’s Deep Space Exploration Laboratory (DSEL).
“Its flight data will provide important support for technical research such as orbit maintenance and control, autonomous navigation, and navigation of spacecraft in complex gravitational environments,” DSEL stated.
This was backed up by tracking by amateur satellite tracker Scott Tilley, who has been tracking the spacecraft, and found it in 3:1 resonance orbit with a 9-day period. The spacecraft was also spotted by asteroid observers and designated as preliminary object A11npTg before being confirmed as Tiandu-1.
DSEL also claimed it was the first spacecraft to enter such an orbit, but NASA’s Interstellar Boundary Explorer (IBEX) spacecraft has already operated in a similar, but not identical orbit to the 3:1 resonance orbit.
Tilley also discovered DRO-B—initially launched to test out communications and navigation in a distant retrograde orbit around the moon—is in a 3:2 resonance orbit and is making a tour of the E-M Lagrange points L3, L4 and L5; gravitationally stable areas in space due to the influences of the Earth and moon that may host future infrastructure.
DSEL, also known as Tiandu Laboratory, operates the Tiandu spacecraft. DSEL said of the Tiandu-1 mission that the testing of the orbit was of “great significance to the future development of the Earth-moon space infrastructure construction.”
The DRO satellites, meanwhile, were developed and operated by a branch of the Chinese Academy of Sciences (CAS). While CAS has detailed the dramatic salvage of the satellites from being stranded in an elliptical Earth orbit to reaching their intended lunar orbits, it has not appeared to have provided an update on its further activities after completing its main activities in DRO.
Despite the success of the mission and its rescue, there are issues. DRO-B is not active all the time, Tilley told SpaceNews, based on his observations. Accounts of the rescue of DRO-A and DRO-B note that both DRO-A and B suffered damage to their solar panels due to the issue with the upper stage for their launch. This could be the reason for the on-off nature of DRO-B’s operations, Tilley notes.
Tilley also tracked Tiandu-2, which launched along with Tiandu-1. That spacecraft may be off its original orbit and suffering other issues. “It was rotating,” Tilley noted in one observation. “So not all these missions are going off perfectly.” DSEL has not updated on the operations of Tiandu-2.
China also has the Queqiao-1 and Queqiao-2 satellites in lunar orbits. The latter will support China’s next landing missions, Chang’e-7, launching next year, and Chang’e-8, in 2028-29. Both Chang’e missions will target the lunar south pole.
