Chinese Satellites Complete First High-Altitude Rendezvous For Possible Groundbreaking Refueling

Two Chinese satellites, SJ-25 and SJ-21, have reportedly completed the first autonomous high-altitude orbital docking. "Although unconfirmed, this is thought to be the first orbital refueling at such a height -- the two satellites are currently over 20,000 miles from Earth," reports ExtremeTech. From the report: Orbital refueling is an important component in keeping satellites and space stations in low Earth orbit flying, but any efforts beyond that have been merely speculative until the past few years, when serious efforts from a range of private and national entities have explored its possibilities. China may have gotten ahead of the curve with this latest docking, though, in an impressive world first that raises serious concerns for satellites from nations and entities that align themselves differently from China's goals and ambitions.

In January, a satellite designated SJ-25 was launched "for the verification of satellite fuel replenishment and life extension service technologies," according to the Chinese state-owned designer, Shanghai Academy of Spaceflight Technology (via Ars Technica). Sometime last week, it matched orbits with the SJ-21 satellite, which previously conducted space debris maneuvering tests in 2021 and has remained in a geosynchronous orbit ever since.

Last week, the two satellites matched orbits and seemingly docked together. Analysts believe the newer SJ-25 has likely proven refueling is possible even for geosynchronous satellites without the need for a manned crew to facilitate it. In an effort to prove this, two US Space Force's inspector satellites have positioned themselves in closer orbits to SJ-25 and SJ-21 for improved optics. [...] China continues to suggest these missions are part of a debris clean-up program, though it hasn't publicly made any statements about the recent alleged docking and refueling to celebrate its successes. If it doesn't, the only way we'll know if a refueling maneuver was successful is if the SJ-21 satellite unshackles from its younger sibling and performs fuel-demanding maneuvers that its previously estimated fuel levels shouldn't allow for.

Hydrazine

[quenda]

The sJ25 has transferred hydrazine propellant to a satellite in geostationary orbit.

This is not to be confused with the sort of in-orbit refueling that SpaceX will need to do for Starship to reach the moon and beyond.
    Cryogenics (liquid oxygen and methane) are a whole other game.

That's not a height,

[Mr. Dollar Ton]

that's a distance, there is a large decrease ( (20k miles/ 6400km) squared or about 25 times) of the acceleration acting on mass near Earth's surface and in this orbit.

Hack/dismantle

[stabiesoft]

I imagine the ability to glom onto another satellite could be used for things other than refueling. I expect the US/EU is watching this very carefully, and a bit envious if they don't have the ability themselves already, just classified so no one knows.