China's Shijian satellites separate after mysterious orbital docking mission

Two Chinese satellites, Shijian-21 and Shijian-25, have separated in geosynchronous orbit after months of being docked together. The event was observed from the ground on 29 November 2022. Little is known about the mission due to limited transparency from Chinese authorities. Shijian-21 was launched in October 2021. Its primary mission involved towing a defunct Beidou-2 G2 navigation satellite to a graveyard orbit. Shijian-25 followed in January 2022, designed to test on-orbit refuelling and mission extension technologies in geostationary Earth orbit (GEO).

The pair operated near the geostationary belt at 35,786 km above Earth’s equator. Their orbital inclination of 4.6 degrees matches that of some Chinese and US satellites, hinting at possible future interactions. While docked, the satellites appeared to conduct low-profile refuelling tests.

Optical observations confirmed their separation late last year. The move may signal the completion of a groundbreaking refuelling operation in GEO, a first of its kind. On-orbit servicing, such as refuelling, can prolong the life of high-value spacecraft. The separation of Shijian-21 and Shijian-25 suggests progress in this capability. The mission’s details, however, remain largely undisclosed.