Russian Cosmonauts Found the Causes of Coolant Leak from Nauka

On October 25, at 17:55 UTC, cosmonauts Oleg Kononenko and Nikolai Chub exited the airlock of the Poisk module, in the Russian segment of the ISS, to carry out EVA no. 61. The spacewalk aimed at verifying the nature of the coolant leak, which occurred on October 9, 2023, from the auxiliary radiator installed this year in the Nauka module.

A helmet cam view from cosmonaut Oleg Kononenko shows spacewalker Nikolai Chub inspecting and photographing the external radiator on the Nauka module. Watch live… https://t.co/cx8fKGlctT pic.twitter.com/xGpUvABOXu
— International Space Station (@Space_Station) October 25, 2023

The coolant curse

It seems like a curse: since December 14, 2022, three accidents of this type have occurred in the Russian section of the International Space Station.

The first, precisely on Dec. 14, 2022, affected the circuit, called SOTR, of the service module (PAO) of the Soyuz MS-22 spacecraft. To avoid problems, it was deemed appropriate to send back to Earth the Soyuz empty, leaving its crew waiting for the Soyuz MS-23 which would bring them safely to Earth 371 days after the start of their mission.

The Soyuz MS-22 crew ship is pictured in the foreground docked to the Rassvet module as the International Space Station orbited 264 miles above Europe. In the background, is the Prichal docking module attached to the Nauka multipurpose laboratory module. Credits: NASA Johnson via Flickr — *The Soyuz MS-22 docked to the International Space Station. Credits: NASA*

Singular coincidence, almost at the same point, another loss occurred, on February 11, 2023, on the Progress MS-22 which was already sealed and ready for re-entry. In both cases, the external inspection established that the cause of the liquid leaks was due to micrometeorite impacts.

The auxiliary radiator that waited outside for many years

The radiator involved in the leak, RTOd (from the Russian Russian Radiatsionny Teploobmennik Dopolnitelny i.e. additional heat exchanger radiator), has a long history behind it. It was launched in 2010, together with the Rassvet module, on board a Shuttle and remained there, folded, to be mounted on the NEP scientific module. Following the latter’s cancellation, it was left anchored to Rassvet for 13 years, awaiting the arrival of the MLM Nauka module.

Detail of RTOd junction tubes during assembly on Earth. Credit: Roscosmos — *Detail of RTOd junction tubes during assembly on Earth. Credits: Roscosmos*

Finally, between April and May 2023, the radiator was transported from the Rassvet module to the Nauka module, installed, and made operational. But, perhaps, it was destined not to work for long.

Tablecloths are not enough

From an initial external investigation, the two cosmonauts did not detect any obvious damage on the surface of the radiator which was not leaking as, at the time of the leak, it was excluded from the cooling system.

Work plan outside Nauka module. Credit: Roscosmos — *Work plan outside Nauka module. Credits: Roscosmos*

However, as soon as the inlet valves began to be progressively opened, large bubbles of liquid, some approximately 20 cm in size, were seen forming from the joints between two panels of the radiator.

“Tablecloths are not enough!” exclaimed one of the two cosmonauts to signify that the material available, tablecloths, brought to absorb the leak, had quickly become soaked in the leaked liquid.

Furthermore, the suit, specifically a glove and the helmet visor, had been contaminated by the liquid itself which had been deposited along the safety rope.

Coolant leaks from the ROTd radiator as seen by cosmonauts. Credit: Nasa/Roscosmos — *Coolant leaks from the ROTd radiator as seen by cosmonauts. Credits: NASA/Roscosmos*

At this point, the MCC-M of Moscow asked the two cosmonauts to close the circuit and return to avoid further contaminating the equipment, making it impossible to subsequently shelter it inside due to the dangerous fumes of the liquid, isooctane, a hydrocarbon (C₈H₁₈) at room temperature colorless but highly flammable once evaporated.

The causes of the coolant leak

Certainly the long stay of the RTOd outside the Rassvet module, for more than 13 years, exposed to solar radiation and numerous thermal shocks in the folded position, may have caused microfractures in a component such as the lateral connections of the various segments.

RTOd radiator in the folded position outside the Rassvet module. Credit: Roscosmos/Russianspaceweb — *RTOd radiator in the folded position outside the Rassvet module. Credits: Roscosmos/Russianspaceweb*

In itself, the failure does not affect the functioning of the ISS, nor that of the Nauka module itself. It is an auxiliary component, intended to perform a fundamental function in the planned but never realized NEP module, but redundant for the Nauka.

Some additional problems will arise from the materials, the safety cable, and part of the suit, contaminated by Isoctane.

If the tablecloths were abandoned in the space, the cable was anchored outside so as not to bring it back inside where it would cause contamination of the atmosphere. Fortunately, the helmet and gloves of the Orlan suit have been adequately reclaimed with other tablecloths present inside the airlock of the Poisk module, allowing the cosmonauts to return on board safely.

The conclusion of the EVA

The work of Kononenko and Chub continued for more than seven hours. A minisatellite, called Paurus-MGTU, was launched and, subsequently, attempted to deploy a radar which, however, was not completely successful as one of its three segments remained partially folded. After 7h 41′ the cosmonauts were ordered to return. A further attempt will be made to deploy the radar antenna in the next EVA.