China's Shijian satellite pair appears to dock in orbit for historic refuelling mission



Shijian-21 and Shijian-25 'appeared visually merged in optical sensor data', space tracking firm says, a feat US seeks to match by 2026

Phoebe Zhangin Shenzhen
Published: 9:08pm, 13 Jul 2025|Updated: 9:10pm, 13 Jul 2025

Two Chinese satellites may have docked in geostationary orbit for a historic refuelling mission, an autonomous satellite servicing feat the United States has yet to achieve.

China's Shijian-21 and Shijian-25 "appeared visually merged in optical sensor data" between July 2 and July 6, US-based space situational awareness software provider COMSPOC said on Saturday in a social media post.

"Given the prolonged RPO time, SJ-21 and SJ-25 may have docked," it said, using the acronym for "rendezvous and proximity operations".

The two probes were observed carrying out such operations in geosynchronous orbit in June and July "with multiple close approaches", it added.

The first close approach was observed on June 11, when Shijian-25 continued its "steady drift towards" Shijian-21, and the two came within 1km (0.6 mile) of each other on June 13 before separating 90 minutes later, according to COMSPOC.

US surveillance satellites USA 270 and USA 271 flanked the Chinese satellites from east and west at the time and were positioned for optimal viewing angles, the company said.

According to optical tracking images from Swiss space surveillance firm s2a systems, the Chinese satellites, both orbiting at an altitude of 35,786km (22,236 miles) above the equator, carried out another round of close-proximity operations on June 30.

It said the two came within extremely close range after days of closing in on each other.

"After a day with small but relatively constant distance yesterday, the two objects came closer again today and can no longer be separated by our instrument since about 11:00 UTC (7pm Beijing time)," s2a systems said on July 2.

An updated post on July 5 said that no significant changes were observed.

Launched in January, Shijian-25 is designed to test "on-orbit refuelling and satellite life-extension technologies". The mission aims to verify capabilities for maintaining and prolonging the operational lifespan of satellites already in orbit as a way to reduce costs, improve sustainability and help address growing concerns over space debris.

Shijian-21 was sent into orbit in October 2021, with an aim to "mainly test and verify space debris mitigation technologies". It used up much of its propellant the following January while towing a defunct BeiDou navigation satellite into a higher "graveyard" orbit.

Satellite-to-satellite refuelling in high orbit presents extraordinary technical challenges, such as the need for precise docking and fluid transfer between uncrewed spacecraft in microgravity.

Beijing has prioritised space debris mitigation and refuelling efforts, primarily using the Shijian satellites to scoop up debris with robotic arms and nets or eliminate it with lasers.

According to American media reports, the US Space Force requested about US$20 million in the fiscal 2025 budget to fund early research and development of on-orbit satellite servicing technologies, including refuelling. Demonstration tests are expected to begin as early as next summer.

The US has been closely watching the Chinese experiments, as the technologies could also be used for anti-satellite warfare to disable probes critical for positioning, navigation and timing; command, control and communications; as well as missile early warning and other vital military functions.

Nasa's similar OSAM-1 (On-orbit Servicing, Assembly and Manufacturing 1) mission was cancelled in 2023 after years of delays and technical challenges. Sixteen years earlier, the US Defence Advanced Research Projects Agency had carried out an autonomous satellite servicing demonstration in low-Earth orbit. The 2007 operation, known as Orbital Express, was successful but less complex.

https://www.scmp.com/news/china/scie...elling-mission


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