Further to NG's MEV-1 and MEV-2 projects already mentioned, China joined this club in 2021-22.
Although termed "space debris mitigation" by the PRC, its uses otherwise, just like for MEV-1 and -2, are obvious.
China’s Shijian-21 towed dead satellite to a high graveyard orbit
China’s Shijian-21 space debris mitigation satellite has docked with a defunct Chinese satellite to drastically alter its geostationary orbit, demonstrating capabilities only previously exhibited by the United States.
In late December (2021), Shijian-21 approached the defunct Beidou-2 G2 navigation satellite, matching its orbit and rendezvousing with, and eventually docking with the spacecraft
Shijian-21 performed a large burn Jan.22, taking the Beidou-2 G2 satellite 3,000 kilometers above the GEO belt.
The docking and subsequent engine burn — which was unusually large, taking it beyond the usual “graveyard” orbit of 300 kilometers above GEO
“You could look at China working to develop the capability to remove inactive satellites on orbit as a way in which it is being a responsible space actor and cleaning up debris that it caused. Or you could use the lens that a lot of the US-based China watchers use and say that this could indicate that China is developing an on-orbit offensive capability.”
USA 270, Chinese Shiyan-12 encounter
“What we’re showing here is counterspace technology. So, they’re kind of employing a tactic, technique [and] procedure, or TTP, as it’s known by the U.S. Department of Defense, and are showing that they’ve got the exquisite, timely and responsive SSA to understand events that are unfolding.”
The closest approach between the U.S. and one of the Chinese satellites was around 73 kilometers, according to COMSPOC. Not close enough to threaten a potential collision, but enough for one party to decide if it wanted to leave the vicinity to avoid potential intelligence gathering or other activities by the other.
In 2021 Astroscale did a tech demo in space of a magnetic capture and release using a CubeSat as a target.
We are excited to announce that ... our #ELSAd spacecraft successfully demonstrated repeated magnetic captures in orbit today!
The ELSA-d spacecraft of Japan-based startup Astroscale has successfully captured a simulated piece of space junk, completing the first phase of a demonstration mission that could pave the way for a less cluttered future in orbit.
Other methods, from the Soviet era:
Other satellite defense techniques studied by TashKBM were electronic countermeasures, measures to reduce the radar cross-section of satellites, the deployment of decoys, the use of aerosol particles to obscure satellites from attacking vehicles and what are described as “heat screens.”
Few details have been revealed about the Nauka experiments related to satellite defense. Androsov mentions tests of “space-to-space projectiles,” “transformable and inflatable structures,” as well as radar-absorbing materials.
plasma stealth technology.
Just like the plasma that naturally builds around a spacecraft during re-entry can cause communication blackouts, artificially created plasma clouds can theoretically absorb radar waves aimed at satellites in orbit. The principle was tested using so-called magneto plasma dynamic (MPD) engines, which expel plasma at very high speeds
Soviet-era publications had already described one such plasma engine having flown on Cosmos-728 in April 1975 and later publications identified another one carried by Cosmos-780 in November/December 1975.
Mounted on the forward end of the Nauka modules, the 2.5-kilowatt MPD engines were fueled by potassium and used for experiments called Kren (“roll”), at least one purpose of which was to test the stealthy effect of plasma clouds.
Testing plasma stealth technology on Soyuz
A similar test of plasma stealth technology was conducted in 1976 on an uncrewed Soyuz spacecraft
Fed by lithium, the 17-kilowattengine was successfully ignited on December 13, ejecting ions at a speed of up to 60 kilometers per second. According to Androsov, the resulting plasma cloud made the vehicle temporarily disappear from radar screens, but the 2012 article says it also had the unwanted effect that the command to shut down the engine did not immediately reach the vehicle, leaving little propellant and battery power for a second burn that turned out to be far less effective.
explosive charges were mounted on short booms extending from either side of the interceptor satellite. The Soviet Union launched about 20 interceptors under the IS program between 1968 and 1982, with several of them successfully destroying specially launched target satellites.
14K168 Burevestnik (2011)
is an umbrella name for an ASAT program that includes both space-based and non-space-based elements
a space-based system that itself seems to have two components (Burevestnik-M and Burevestnik-KA-M)