Experimental Chinese satellites Shijian-21 and Shijian-25 undocked in geosynchronous orbit after several months of being in a docked state, during which, likely, inconspicuous refueling tests were conducted directly in orbit.
During the first half 2025 Shijian-21 and Shijian-25 performed approach and maneuver operations near each other, and at the end of June - at the beginning of July, probably, docked: from that moment they were practically impossible to distinguish from Earth, what, according to independent trackers, was the beginning of the planned refueling tests. Later, the docked pair performed energy-intensive maneuvers to change the plane of the orbit, reducing the inclination of the orbit. Optical observations from the Earth, conducted 29 November by the Swiss company S2a systems (specializes in optical space tracking systems), showed, that the two satellites separated again in geosynchronous orbit near the geostationary belt (GEO, height 35 786 km above the equator). The orbits of both devices have an inclination of 4.6° relative to GEO. Undocking may signal the successful completion of the world's first refueling tests in geostationary orbit. However, neither the Chinese space agency, neither satellite manufacturer has commented on the mission since the launch of Shijian-25 in January 2025 year.
Lack of openness means, that there is very little information about the mission. Such opacity is also worrying: although on-orbit maintenance may have a purely civil purpose, the very ability to approach, docking and manipulating objects in GEO has obvious military applications. Communication satellites are located on GEO, meteorological, remote sensing of the Earth and the system of early warning of a missile attack.
Further tracking of satellite behavior and changes in their orbits, especially the older Shijian-21, can provide an answer as to whether the refueling tests were successful. A successful test would be a major breakthrough for China's space capabilities. Maintenance in orbit (refueling, orbit correction, moving) will allow to significantly extend the service life of expensive and strategically important devices, such as communication satellites, and will also enable the reuse of old satellites.
According to the estimates of the company Integrity ISR in August, performed plane change maneuvers brought the SJ-21/SJ-25 pair into an incline, close to a number of Chinese GEO satellites, in particular technological demonstrators TJS-11 and TJS-19, military optical satellite Yaogan-41 and experimental Shijian-23 - all of them were developed by the Shanghai Academy of Space Technology (Hes), which also created the SJ-21 and SJ-25. These vehicles may become potential targets for further rendezvous and refueling operations. Other observers note, that the inclination of the orbits of Shijian-21 and Shijian-25 also coincides with some American satellites, that is, approaches to them are also possible in the future.
Orbital servicing and refueling technologies potentially reduce costs, increase the sustainability of space operations and reduce the amount of debris. At the same time it is known, that the People's Liberation Army of China is actively developing these technologies and simulators for refueling satellites as a peaceful, as well as in wartime.
Source: https://spacenews.com