Spacewalking cosmonauts find radiator coolant leak

Russian cosmonauts Oleg Kononenko and Nikolai Chub work outside the International Space Station on Oct. 25, 2023. Image: NASA TV

Two Russian spacewalkers floated outside the International Space Station Wednesday and isolated a leaking radiator as planned, apparently causing residual coolant still trapped inside to make its way to the leak site and spew out into space.

Cosmonaut Oleg Kononenko planned to sop up the pooling coolant with a cloth towel, but was told to leave the area immediately when he reported some of the liquid had made it onto a safety tether. He said none had reached his suit.

The tether was secured in a bag and procedures were already in place to make sure the cosmonauts’ spacesuits were clear of any such contamination before they re-entered the space station at the end of the spacewalk.

In the meantime, Kononenko and crewmate Nikolai Chub pressed ahead with work to attach a small synthetic aperture radar antenna to the hull of the Nauka module. One of its four panels failed to fully deploy and lock in place, and officials said adjustments would be made in a future spacewalk.

Finally, Kononenko and Chub released a small student-built “nanosatellite,” but the solar sail propulsion system it was designed to test failed to deploy. After making a final attempt to coax the balky radar panel into place, the cosmonauts called it a day.

A small nanosatellite was successfully launched from a spring-powered deployer, but the solar sail it was designed to test failed to deploy. Image: NASA TV.

Kononenko, making his sixth spacewalk, and Chub, making his first, began the excursion at 1:49 p.m. EDT when they opened the side hatch of the Poisk airlock compartment to the vacuum of space.

The radiator in question was launched with the Russian Rassvet module aboard the space shuttle Atlantis in May 2010. The radiator and a small experiment airlock remained stored on Rassvet until earlier this year when spacewalking cosmonauts attached both to the Nauka multi-purpose laboratory module.

The radiator’s installation went normally and valves were opened to route coolant from Nauka into its unfolded panels. But on Oct. 9, flight controllers noted flakes streaming from the area of the radiator. The flakes turned out to be frozen coolant that was spewing overboard.

Kononenko and Chub checked and reset coolant loop valves, adjusting them to isolate the radiator from supply lines and photographing the leak site to help engineers figure out what caused it.

Kononenko initially reported “the radiator is clean. I don’t see anything … I do not see any traces of coolant.”

But he reported numerous “black spots” on one radiator panel and after the valves used to isolate the radiator from its coolant lines were adjusted, droplets of coolant could be seen leaking from a line connecting two radiator panels.

The droplets combined to form a fairly large bubble around the leaking coolant line. Kononenko said the bubble was too large to sop up with the towel he had planned to use. Instead, the cosmonauts simply left it as is while engineers on the ground began considering possible courses of action.

Particles of coolant flake away from a large bubble that formed on the leaking radiator during a spacewalk by two cosmonauts. Image: NASA TV.

What might have ruptured the coolant line in the first place was not immediately known.

It was the third coolant leak in less than a year for the Russians, starting with a massive rupture that disabled a Soyuz crew ferry ship last December. A similar leak developed on an unpiloted Progress cargo carrier earlier this year.

The presumed cause of the Soyuz leak was a micrometeoroid impact. The Russians have not addressed the possible cause of the Progress leak or the one affecting the Nauka radiator. But it seems extremely unlikely micrometeoroids could have caused three such incidents in similar systems.

In any case, shortly after the latest leak occurred the Russian space agency Roscosmos said in a post on Telegram that the lab’s primary coolant loop was not affected and “the crew and the station are not in any danger.”

Kononenko and Chub were not planning any sort of repair. Their primary objective was to find and document where the leak originated and to isolate the radiator from coolant supply lines to prevent any future problems.