Launched in 2018, a Chinese spacecraft has been inspecting other nations' satellites high above Earth in geostationary orbit (GEO), Space.com reported. 

Vaguely touted as a communications experiment satellite, Tongxin Jishu Shiyan Weixing-3 (TJS-3), was sent up into geostationary orbit in late 2018. It then released a small subsatellite, possibly to help test TJS-3's capabilities. 

According to the Space.com report, orbital data reveals that TJS-3 has been making close approaches to American satellites in recent months. For example, the Twitter account Orbital Focus notes that the satellite has been drifting along the geostationary belt, but pausing to take a closer look at satellites USA 233 and USA 298, both alleged to be military communications satellites operated by the U.S. Space Force.

Satellite Dashboard, a web tool that analyzes space situational awareness (SSA) data, revealed that TJS-3 approached as close as 3.8 miles (6.2 km) to USA 233 on October 31, last year. 

US, Russian and Chinese satellites have all increasingly been scouting each others' satellites in the GEO in recent years, using close approaches to attain images and other data, writes Andrew Jones for Space.com, adding that little is known about the TJS-3 satellite, but the U.S. and other nations are most likely to be monitoring its movements closely.

Satellites in the GEO operate at 35,786 kilometers above Earth, where their velocity matches the rotation of the planet and makes them appear fixed over one point on the surface below. This orbit is thus highly prized for its use for communications and other purposes.

Subsequently, a spacecraft that either raises or lowers its orbit a few tens of miles will be able to drift west or east respective to other satellites, allowing a satellite over time to sweep past others and take a look. 
 

Image courtesy: ESA – L. Boldt-Christmas