Space Force has been increasingly turning to commercial space companies to provide a variety of data and services to boost its situational awareness, and to that end, Joint Task Force-Space Defense awarded Exoanalytic Solutions a contract in 2021 to provide space domain data. “Comms, data relay, remote sensing, and even ISR and some other things — [these] capabilities are increasingly available in the commercial market,” Space Force deputy Lt. Gen. David Thompson said last year.

SJ-21’s recent maneuver raises questions and concerns about these types of satellites and their potential for military use. Todd Harrison, director of CSIS’s Aerospace Project, told Breaking Defense that SJ-21’s actions present “more questions than answers,” adding that while we can observe the satellite’s actions, “the intent behind it and what China plans to do with this technology is a more subjective assessment.”

This isn’t the first time SJ-21 has made headlines with its questionable behavior. In November 2021, just a month after its launch, an unknown object was seen orbiting alongside SJ-21. At the time, Space Force designated the unidentified object as a spent apogee kick motor, but it was also reported that it might have been an experimental payload designed to test SJ-21’s ability to perform remote operations and manipulate other satellites.

Analyzing the potential applications of these dual-use satellites is difficult. As CASI notes, while SJ-21’s previous behaviors demonstrate “technology to potentially enable weapons or reconnaissance capabilities,” they are also perfectly in line with China’s peaceful economic and scientific goals in space, particularly related to debris removal.

Still, if SJ-21 can grab a dead satellite and move it out of orbit, there is likely little stopping it from doing the same thing to an operational one the American military depends upon. It’s important to note that the United States is also exploring on-orbit servicing capabilities that will likely prompt similar concerns from America’s competitors. Northrop Grumman is developing a satellite featuring a DARPA-made robotic arm for a planned launch in 2024 that is capable of “detailed inspections, relocations of client vehicles or simple repairs such as releasing a solar array that is stuck or an antenna that doesn’t deploy properly.”

The fact that China has these capabilities in orbit now underscores concerns the Pentagon has been voicing in recent years about China’s rapidly advancing space capabilities. James Dickinson, commander of United States Space Command, told Congress last year that Chinese satellites like SJ-21 and others “could be used in a future system for grappling other satellites.” As early as 2013, there have been reports of Chinese satellites using robotic arms to grab other satellites. A robotic arm launched aboard the Tianhe module of China’s Tiangong space station has displayed similar capabilities.

Those concerns aren’t unfounded. In another direct example of this potential threat, an American spy satellite was shadowed closely in 2020 by a Russian “space apparatus inspector” believed to have capabilities similar to SJ-21. Maneuvering one satellite close to another in orbit is a technologically complex proposition, and there is always the possibility of an unintentional collision occurring during one of these operations. There are also concerns about adversary satellites with more destructive capabilities such as high-powered microwaves or the ability to launch projectiles. Any satellite that has the ability to maneuver in close proximity to another could potentially carry out a variety of attacks on it such as jamming its transmissions, blinding its sensors, spraying aerosols on its solar panels and optics, physically manipulating it, or moving it out of orbit as in the case of Shijian-21’s recent operation.