China’s landmark orbital refuelling mission: why US spy satellites hover nearby

China appears on the verge of carrying out a historic satellite-to-satellite refuelling mission in high orbit, a potential advance that has prompted the US to deploy two military surveillance satellites nearby to watch.

The Shijian-25 satellite was launched this year to test on-orbit refuelling and mission-extension technologies, and has been drifting towards Shijian-21. The two satellites have nearly synchronised orbits and are primed for rendezvous and docking, according to public tracking data from the US military’s Space-Track.org website.

Shijian-25 is expected to use its robotic arms to latch onto Shijian-21 and replenish its fuel. The latter used up much of its propellant in 2022 while towing a defunct BeiDou navigation satellite into a higher graveyard orbit.

Meanwhile, United States surveillance satellites USA 270 and USA 271 have flanked the two Chinese satellites from the east and west after conducting multiple manoeuvres last week and are positioned for optimal viewing angles, according to a social media post by COMSPOC, a Pennsylvania-based space situational awareness company.

Jonathan McDowell, a Harvard astronomer and space historian, said the behaviour of the American satellites was highly uncommon.

“As far as we know, it is very unusual for this kind of close-range observation by coordinated US space assets – it hasn’t been documented before,” he said on Wednesday.

First conceptualised by Nasa in the 1960s, on-orbit refuelling technology is considered critical not only for extending satellite lifespans and reducing operational costs, but also for improving long-term sustainability in space by minimising orbital debris.

In 2007, the Defence Advanced Research Projects Agency (DARPA) successfully carried out the Orbital Express mission in low Earth orbit, performing the first-ever autonomous docking and fuel transfer between two specially designed test satellites.

  

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