Temperatures in a Russian Soyuz crew ferry ship docked at the International Space Station — a lifeboat for three of the lab's seven crew members — remain within safe limits despite ain the spacecraft's cooling system, officials said Thursday.
The leak developed around 7:45 p.m. EST Wednesday amid preparations for a planned 6-hour and 40-minute spacewalk by cosmonauts Sergey Prokopyev and Dmitri Petelin to move a radiator from the Rassvet module, where the Soyuz MS-22/68S spacecraft is docked, to the new Nauka laboratory module.
With the cosmonauts suited up in the Poisk airlock compartment, Russian flight controllers noted a low-pressure warning in an external Soyuz coolant loop, and then saw a sudden stream of coolant venting into space in a shower of icy particles.
The leak looked especially dramatic under certain lighting conditions, showing up in a NASA television camera view as a jetting shower of countless shiny particles, presumably frozen coolant. The leak was not clearly visible in another view, from another angle and with different lighting.
But there was no doubt a major leak was present. It continued for several hours and Russian flight controllers called off the spacewalk while engineers monitored telemetry and video.
More than 12 hours later, the origin and cause of the leak remained unclear. Options ranged from a space debris impact to an isolated hardware failure of some sort.
The Soyuz carried Prokopyev, Petelin and NASA astronaut Frank Rubio to the space station on, and it is required to carry them back to Earth at the end of March. In the meantime, the ship serves as a lifeboat in case of an emergency that might force the trio to abandon the ISS ahead of schedule.
Coolant systems are critical to all spacecraft in order to cope with a wide range of temperatures, such as when vehicles are in direct sunlight, the cold darkness of the Earth's shadow, or during re-entry. It's not yet known how much coolant, if any, might remain in the system, or how temperatures will respond to different sun angles in the station's orbit.
But telemetry in the wake of the leak showed temperatures in the Soyuz spacecraft remained within safe limits.
The Russian space agency Roscosmos "is closely monitoring Soyuz spacecraft temperatures, which remain within acceptable limits," NASA said in a blog post Thursday. "NASA and Roscosmos continue to coordinate external imagery and inspection plans to aid in evaluating the external leak location."
While NASA did not address the issue directly, the Soyuz presumably is flightworthy as is, but no other details were immediately available.
Overnight Wednesday, cosmonaut Anna Kikina, who flew up to the ISS aboard a SpaceX Crew Dragon ferry ship with three NASA-sponsored crewmates, used a new European Space Agency-built robot arm on the Nauka module to visually inspect the Soyuz.
NASA said an additional inspection by the Canadian-built robot arm on the U.S. segment of the lab complex is being planned. In the meantime, Crew Dragon astronaut Josh Cassada and Rubio are pressing ahead with plans to carry out a spacewalk of their own Monday to continue an ongoing solar array system upgrade.
"The crew aboard station completed normal operations Thursday, including participating in science investigations and research," NASA reported. "Specialists are working through robotic plans ahead of Monday's spacewalk to best optimize for upcoming station operations and the Soyuz inspection."
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