Shi Jian 21 (SJ 21)

SJ 21 (Shijian 21) is a Chinese experimental space debris mitigation satellite which has docked with a defunct Chinese satellite to demonstrate removal of dead satellites from geostationary orbit.

It was launched in October 2021 on a CZ-3B/G2 rocket. Its duty is the validation of on orbit space debris reduction technologies.

Orbital tracking shows that Shijian-21 has been conducting sophisticated rendezvous and proximity operations (RPO) with a co-launched subsatellite and other objects in and around the geostationary orbit.

In late December, Shijian-21 approached the defunct Beidou-2 G2 navigation satellite, matching its orbit and rendezvousing with, and eventually docking with the dead satellite. After docking it performed an engine burn on 21 January 2022 which took the defunct satellite beyond the usual graveyard orbit of 300 kilometers above GEO. Shijian-21 then undocked from Beidou-2 G2 on 26 January 2022, leaving the defunct satellite in the graveyard orbit. Shijian-21 has since returned to GEO.