China set to launch Shenzhou 23 astronauts to Tiangong space station this weekend

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China is preparing to launch its next crew to the Tiangong space station as soon as Sunday (May 24), in a mission that will relieve astronauts who have been in orbit a month longer than planned, and potentially send one astronaut on China's first year-long spaceflight.

The 203-foot-long (62 meters) Long March 2F rocket that will launch the Shenzhou 23 mission was transferred 0.93 miles (1.5 kilometers) by rail from the vertical integration building to the pad at Jiuquan Satellite Launch Center in the Gobi Desert on May 16.

Teams performed a pre-launch rehearsal on Wednesday (May 20), with the China Manned Space Agency (CMSA) declaring that all facilities and equipment at the launch site are in good condition.

The Shenzhou 23 mission will send the next trio of astronauts to Tiangong to begin a six-month-long stay aboard the space station. CMSA has yet to reveal the crew for the mission. The three astronauts will be announced when they meet the press at Jiuquan around a day before launch. The unnamed trio also underwent medical tests and other rehearsals on Wednesday.

China has not officially announced a time and date for the launch of Shenzhou 23, stating only that the mission will be launched "at an appropriate time in the near future." However, airspace closure notices currently indicate that launch will take place around 11:10 a.m. EDT (1510 GMT, or 11:10 p.m. Beijing time) on Sunday.

The launch could also mark the start of a historic human spaceflight for China: One of the three astronauts could be starting a one-year stay in orbit, which would be a first for the country. This is because Shenzhou 24, due to launch late this year, may be used to send a Pakistani astronaut to Tiangong for a short-duration visit. This first international visitor to Tiangong will arrive on Shenzhou 24 but then take the seat of one of the Shenzhou 23 astronauts days later when the spacecraft returns to Earth, leaving one Shenzhou 23 astronaut to complete a year in orbit.

The launch of Shenzhou 23 will also signal the end of what has become China's longest human spaceflight mission to date — the emergency-impacted Shenzhou 21.

The new crew will take control of Tiangong from the Shenzhou 21 astronauts, who saw their Shenzhou 20 colleagues use their Shenzhou 21 spacecraft to get home after a suspected debris impact damaged the Shenzhou 20 vehicle. The uncrewed Shenzhou 22 was later sent to Tiangong to provide a lifeboat for the Shenzhou 21 astronauts — Zhang Lu, Wu Fei and Zhang Hongzhang — and is now scheduled to carry them back to Earth on May 29.

Shenzhou 23 will be the 11th crewed mission to fly to Tiangong. The first such flight took place in June 2021, when Shenzhou 12 visited the station's Tianhe core module; two further crewed missions aided assembly of the three-module facility, which was complete by late 2022. Shenzhou 22 was launched uncrewed in an emergency response to provide a lifeboat.

The Shenzhou 23 mission follows shortly after the launch of the Tianzhou 10 cargo spacecraft, which arrived at Tiangong on May 11, delivering nearly seven tons of supplies.