February 23, 2023

— An uncrewed Russian Soyuz spacecraft is now on its way to the International Space Station, having been launched as a "rescue craft" for a damaged ship that is no longer capable of safely returning its crew to Earth.

Soyuz MS-23 lifted off from Site 31/6 at the Baikonur Cosmodrome in Kazakhstan on Thursday (Feb. 23) at 7:24 p.m. EST (0024 GMT or 3:34 a.m. local time on Feb. 24). The spacecraft separated from its Soyuz-2.1a rocket 8 minutes and 48 seconds into flight and deployed its solar panels and communications antenna.

Following a two-day rendezvous, Soyuz MS-23 is expected to autonomously dock to the zenith port of the Poisk mini-research module on the Russian segment of the space station on Saturday (Feb. 25) at 8:01 p.m. EST (0101 GMT Feb. 26).

Update: Soyuz MS-23 autonomously docked at 7:58 p.m. EST (0058 GMT).

Soyuz MS-23 launch to space station. Click to enlarge in new pop-up window. (Roscosmos)

Waiting for the Soyuz's arrival are cosmonauts Sergey Prokopyev and Dmitry Petelin of Roscosmos and NASA astronaut Frank Rubio, who will use it to come home at the end of their now-extended mission in about six months time. The three had been scheduled to land in March until the Soyuz MS-22 spacecraft on which they launched in September 2022 suffered a failure three months later.

On Dec. 14, 2022, as Prokopyev and Petelin were preparing to conduct a spacewalk, Russian flight controllers detected telemetry showing that the exterior coolant system for Soyuz MS-22 was losing pressure. Cameras on the space station showed a steady stream of ammonia ice flakes floating off into space from the base of the spacecraft's heat-dispelling radiator. After three hours, the leak came to an end as the Soyuz exhausted its coolant supply.

A visual inspection of the Soyuz found what appeared to be a 0.03-inch (0.8-mm) hole, which Russian specialists concluded was caused by a micrometeoroid impact. Without coolant, the Soyuz would still be able to return to Earth as normal, but the crew cabin would reach temperatures upwards of 104 degrees Fahrenheit (40 degrees Celsius) for the six hours needed to reach to the ground. Unless a further emergency necessitated using Soyuz MS-22 as a lifeboat, it was decided it would not be used to bring Prokopyev, Petelin and Rubio back to Earth.

Instead, Roscosmos accelerated preparations to launch the next Soyuz, MS-23, which was being readied to carry Prokopyev, Petelin and Rubio's replacements to the station. A target launch date was set for Feb. 20, but then another spacecraft experienced a similar leak.

In a repeat of events, the Progress MS-21 cargo spacecraft vented its coolant on Feb. 11. Subsequent inspections again pointed to a debris impact.

"Progress MS-21, like Soyuz MS-22 before, was exposed to external influences," Roscosmos officials said in a statement.

The Soyuz MS-23 launch was delayed to give engineers time to further study both the Soyuz MS-22 and Progress MS-21 leaks. In the interim, Roscosmos also undocked and deorbited the MS-21 cargo craft after collecting as many photos of the damaged area as possible.

After Soyuz MS-23 docks to the station, Prokopyev, Petelin and Rubio will transfer their seat liners and other equipment from Soyuz MS-22 to MS-23, making the latter both their lifeboat in the case of an emergency and their intended ride back to Earth after spending what will be more than a year in space. Roscosmos plans to undock and land the uncrewed Soyuz MS-22 in late March.

Prokopyev, Petelin and Rubio, meanwhile, will continue conducting science and operating the space station with the other members of the Expedition 68 crew, including NASA astronauts Josh Cassada and Nicole Mann, Japan Aerospace Exploration Agency (JAXA) astronaut Koichi Wakata and Roscosmos cosmonaut Anna Kikina.

Four more astronauts are scheduled to launch to the station on Monday (Feb. 27) as members of SpaceX's Crew-6 mission. Steve Bowen and Woody Hoburg of NASA, Sultan Al Neyadi of the United Arab Emirates (UAE) and Andrey Fedyaev of Roscosmos will replace Cassada, Mann, Wakata and Kikina after they depart as SpaceX's Crew-5 in March.

Soyuz MS-23 is only the second Soyuz spacecraft to fly without a crew in the history of the International Space Station. In 2019, Roscosmos launched Soyuz MS-14 with only cargo and an experimental robot on board to test modifications made for integrating the Soyuz with the then-new Soyuz-2.1a rocket. Prior to that, it had been 33 years since a Soyuz launched without cosmonauts at its controls.

Soyuz MS-23 is the first "rescue craft" launched to the International Space Station, though not the first Russian vehicle sent to bring home a crew. More than 40 years ago, the Soviet Union sent the unpiloted Soyuz 34 to the Salyut 6 station after the prior spacecraft suffered an engine failure. The 1979 mission provided the crew a reliable return craft rather than use an earlier Soyuz with a suspect engine.

Soyuz MS-23 is Russia's 69th Soyuz to launch for the International Space Station since 2000 and 152nd to fly since 1967.