On January 8th China launched another Shijian (“experimental” or “special purpose”) satellite into GSO (geostationary orbit). GSO space is not for orbiting satellites but for those that prefer to remain stationary, which can be done if you are about 35,786 kilometers from earth. This is where any satellite orbited that high will remain above the same area on earth. Since 2016 China has launched four Shijian series satellites into GSO space for vague or sometimes classified missions. The latest one, Shijian-23, was described as on a classified mission. The U.S. Space Force is able to monitor the activities of satellites in GSO space and Shijian-23 was seen to release at least one sub-satellite which could maneuver. China had earlier described Shijian-23 as carrying two sub-satellites but later deleted that information without comment. China would not describe what Shijian-23 and its sub-satellite was up there for. So far, Shijian-23 and its sub-satellite have been moving around up there. Previous Shijian-series satellites were observed moving close to other satellites and apparently inspecting them. Sometimes Shijian series satellites moved other satellites or debris out of valuable GSO areas. This is a useful activity and for China inspecting satellites of other nations is useful and in wartime so is moving foreign satellites out of position or disabling them would also be useful.
Several specialized satellites already put into orbit can grab and move another satellite to a less dangerous location or move a defunct satellite into a less troublesome location. China put the latest of these satellite movers into space during 2021. SJ-21 was put into GSO apace and proved large enough to grab large defunct satellites and move them to less valuable geostationary orbits. In other words, the satellite and earth will rotate together. For some types of satellites these orbits are very useful and when a satellite occupying one of these orbits ceases to function, you have to move it away in order for a working satellite to take its place. SJ-21 demonstrated that it could do the moving. This is quite useful.
More mobile satellites with robotic arms are a welcome new development because they can be used to inspect satellites in trouble and help diagnose the problem and perhaps fix it. Chinese and Russian satellites similar to SJ-21 have already been spotted getting close to satellites belonging to other nations and, in some cases, apparently practicing disabling them. That was not unexpected. While these movement and inspection satellites have a wartime use to disable enemy satellites, the more immediate problem is managing and eventually eliminating a lot of the man-made debris in orbit. The only way to destroy this stuff is to use another satellite to push it close enough to earth for gravity pulls to the surface and moving through the atmosphere at high speeds causes the debris, and in most cases, be completely destroyed. This does not work with the majority of space debris, which is too small to track from earth and too numerous to collect and send into the atmosphere. As this debris crisis becomes more acute, more effort will be put into solutions and those solutions will appear, or there will be fewer operational satellites in orbit. No precise date when the orbit debris crisis becomes critical but when it does show up it shouldn’t be a surprise.
The Shijian series satellites are large enough to operate in GSO and inspect, move or disable other satellites. This was first demonstrated in 2016 with Shijian-17, followed by Shijian-21 in 2021 and now Shijian-23 in 2023.