Shijian-25 Is Likely Refueling Shijian-21
A big milestone for in-space refueling is probably underway.
The Shijian-25 technology demonstration refueling spacecraft and its target, the Shijian-21 space debris mitigation satellite, are currently indiscernible from each other out in geostationary space over China.
Shijian-25 and Shijian-21 became indiscernible to ground-based tracking telescopes at the beginning of the month for their second approach with one another, after similar events in early June. Further sensor data from observing operations in the first week of July suggests prolonged rendezvous and proximity operations leading up to and while the two spacecraft cannot be identified as separate objects.
Since becoming a merged observable object, Shijian-25 and Shijian-21 have remained close together, with space situational awareness firm COMSPOC noting:
“After a brief encounter in mid-June, a second campaign began later that month. On 2 July, both satellites became optically indistinguishable, suggesting docking or sustained close proximity.”
The firm has also observed what it believes to be a small joint alignment maneuver of the Shijian pair on July 3rd, followed by a small joint burn to drift eastwards slightly on July 4th (this drift was halted a few days later1). Since then, the pair has continued to be observed as one, with COMSPOC adding:
“As of 18 July, there’s still no optical confirmation of separation. Orbital behavior remains consistent with a docked or rigidly co-orbiting pair.”
The recent extended period of indiscernibility from one another follows activity in late June, where two spacecraft were only in close proximity to each other for around one and a half hours. Meaning Shijian pair possibly performed a rehearsal of expected maneuvers, or a docking was aborted. No statements were released by the involved agencies or enterprises in China regarding those events.
With over two weeks of now appearing as a single object, along with the joint maneuvers, it’s quite possible Shijian-25 has docked with Shijian-21 recently. Since that docking, the pair has probably prepared for and begun the refueling demonstration, transferring an undisclosed amount of propellant from Shijian-25 to Shijian-21. It’s unknown how long the process will take or what tests will be performed afterward.
Once again, for proper details regarding the test, we will have to wait for official word from one of China's space agencies and enterprises, which may announce the success of the test anywhere from a few days to several weeks afterward. If successful, China will extend its lead in in-space refueling operations, already routinely performed between Tianzhou spacecraft and the Tiangong Space Station (with crew and ground control oversight).
To repeat what I’ve already said about the satellites in geostationary orbit for those just finding out about the events, details on Shijian-25 and Shijian-21 are scarce, but at the 2021 Zhuhai Airshow plans for a similar spacecraft boasted approximately 1,300 kilograms of propellant available for refueling services. Docking operations for the spacecraft described at the airshow say:
"When it arrives within about 2 meters of the satellite, with the cooperation of the robotic arm, it will achieve a close connection with the satellite refueling port and deliver fuel to the satellite.”
Advancements being demonstrated by the Shijian pair have led to officials from the U.S. Space Force whining to for-profit news outlets about a possible lack of superiority in space, despite having an eyewatering budget of forty billion United States Dollars and ending support for similar demonstration missions.
At the moment, SpaceX is leading the U.S. efforts with a transfer of propellant between its Starship vehicles' landing and main tanks, but the vehicle has been stuck with regular failures, holding up orbital flights needed for the next major step in development like a Starship-to-Starship propellant transfer. Meanwhile, Northrop Grumman is in a similar stage of development to Shijian-21, with refueling in space set to come later.
The U.S. had tested an initial form of the technology, which Shijian-25 is demonstrating, back in 1984 aboard the Space Shuttle STS-41G mission with the Orbital Refueling System experiment. That experiment saw some propellant transferred via some astronaut-installed piping between two tanks to simulate a connection to another spacecraft. A Shijian-25-like U.S. mission was in development until March of 2024, when it was cancelled due to technical, cost, and schedule challenges.
Video originally from COMSPOC_OPS on Twitter, videos from Tweets cloned to YouTube for archival.
The firm did not disclose how many days later the halting of the drift was.