SJ-21 / SJ-21 AKM

From early November to late December, 2021, Chinese satellite SJ-21 maintained a close distance with a space object labeled by the U.S. Space Force’s 18th Space Control Squadron as the satellite’s apogee kick motor, SJ-21 AKM, while performing several maneuvers during a westward drift.

Object Name Country Operator
China China Aerospace Science and Technology Corporation (CASC)
Uncataloged N/A

On November 1, 2021, one week after SJ-21 was launched to the geostationary belt in late October 2021, the U.S. Space Force’s 18th Space Control Squadron (18SpCS) published the first orbital element set for a second object mere meters away.1 The second object, which 18SpCS named SJ-21 AKM and identified as SJ-21’s apogee kick motor, maintained an exceptionally close separation distance with SJ-21 for more than six weeks as SJ-21 performed a variety of maneuvers resulting in a westward drift through the GEO belt. When SJ-21 was first launched, Chinese media outlets described its mission as one to “test and verify space debris mitigation technologies,” but made no mention of the purpose of the second satellite, possibly deployed by SJ-21 after orbital insertion as a sub-satellite.

In mid-December, SJ-21 maneuvered away from the second object for several days, before returning on December 22, 2021. On December 28, the two objects separated again when SJ-21 AKM suspended its westward drift, further exhibiting behavior that is unfitting for an apogee kick motor, a launch vehicle component that rarely remains in orbit after orbital insertion. 

  1. Andrew Jones, “An object is now orbiting alongside China’s Shijian-21 debris mitigation satellite,” SpaceNews, November 5, 2021,

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