A specialist from the Russian Mission Control Center told cosmonaut Sergey Ryzhikov that thin strips of paper that were released in the module's access section earlier gathered in three possible leakage sites. They then asked the cosmonaut to use tea leaves to find out if there is a leak in those locations.
Tea leaves were obtained from a sachet by the cosmonauts. They were then moved to the Zvezda service module, which includes sleeping quarters, a kitchen, and a bathroom. The crew then shut the door to the module's transfer chamber.
The tea leaves were suspended in microgravity and examined closely by the crew. The tea leaves were reportedly slowly approaching a small crack in the hull of the module, which was located on an ISS wall. The air was leaking through this very crack.
The astronauts used adhesive tape made of a temperature-resistant material to close the crack. This solution, however, in the long run, will not suffice, and with the next mission, more durable equipment will be delivered to the station, both to help patch the crack and to ensure that no more leaks occur.
A small air leak was first detected at the ISS in September 2019. Russian cosmonauts have since identified two cracks in the access section to the Zvezda module and sealed them both in March 2021, using methods such as releasing tea leaves to help with their search. According to Russia's space agency Roscosmos, the air leak poses no threat to the ISS crew.
Due to the leak, which is equivalent to a hole with a diameter of 0.2 mm, the air pressure at the station drops by 0.4 mm of mercury per day, but this is far from the emergency values of 0.5 mm per minute. To compensate for the leak, the ISS must be regularly filled with air, nitrogen and oxygen. Their reserves are available both at the station and are transported from Earth on cargo ships.
In addition to Ryzhikov and his fellow cosmonaut Sergey Kud-Sverchkov, American astronauts Kathleen Rubins, Michael Hopkins, Victor Glover and Shannon Walker, as well as Japanese Soichi Noguchi are currently on the ISS.