US space tracking has detected an object orbiting alongside a satellite recently launched by China, but its exact purpose remains a mystery.
The Shijian-21 space debris mitigation technology satellite was successfully launched from the Xichang Satellite Launch Center in southwest China’s Sichuan Province on October 23.
After being launched into space by a Long March-3B carrier rocket and entering orbit as planned, Shijian-21 is set to spend most of its time testing and verifying debris mitigation technologies.
The craft was developed by the Shanghai Academy of Spaceflight Technology (SAST), but otherwise not much is known about the satellite, with details being kept underwraps by China.
US Space Force’s 18th Space Control Squadron (SPCS) tracked the satellite in space and catalogued the new object orbiting alongside it on November 1 as an ‘apogee kick motor (AKM)’.
An AKM is used in some launches for a satellite ‘to circularize and lower the inclination of its transfer orbit and enter geostationary orbit (GEO)’, according to Space News, though the object could also be ‘related to space debris mitigation tests, or part of potential counterspace operations tests.’
GEO is the orbit in which satellites appear to remain suspended at a fixed point in space.
It is noted that AKMs usually perform a final manoeuvre after satellite separation to avoid the risk of collision, however, Shijian-21 and the object are side by side in geostationary orbit.
Speaking to Gizmodo, astrophysicist Jonathan McDowell, from the Harvard-Smithsonian Center for Astrophysics, said that satellites ejecting the AKMs after use is ‘pretty rare’, and ‘almost always done by launching to the GEO graveyard, ejecting the motor, and then lowering the payload into GEO proper.’
Graveyard orbits are where satellites are placed once they’ve retired to minimise the risk of collisions with other craft, though McDowell said that to eject an object within GEO itself is a ‘bad idea and very rare.’
Another new cataloged object, this time from the Shi Jian 21 satellite which is drifting at 1 deg W per day in near-synchronous orbit over the Pacific. Could be an optics cover, or a subsat like that from TJS-3.
— Jonathan McDowell (@planet4589) November 3, 2021
The astrophysicist suggested he was doubtful the object was an AKM as it is located 37 miles (60 km) from the satellite, apparently in ‘deliberate synchronisation’, according to McDowell.
He added: ‘If you just ejected and said bye-bye, you’d expect a steadily increasing separation.’
The mystery object’s purpose may be to ‘test rendezvous and proximity operations, refueling experiments or manipulation using a robotic arm or other means’, though a manoeuvre from the object would provide further insight on this. As questions around the object remain, however, it’s likely US space tracking will keep a close eye on it.