Washington, Oct 11 : The astronauts aboard the International Space Station (ISS) are safe after the Russian module on the orbiting lab recently experienced a leak, NASA has said. The agency said its flight controllers at Johnson Space Center in Houston observed flakes emanating from one of two radiators on the Roscosmos Nauka Multipurpose Laboratory Module (MLM) at approximately 1 p.m. EDT on Monday. This was confirmed by NASA astronaut Jasmin Moghbeli who saw the flakes from the cupola windows. The crew was then asked to close the shutters on US segment windows as a 'precaution against contamination'. 'The crew aboard station was never in any danger,' the agency said. Roscosmos confirmed that the observed leak is on Nauka's backup radiator, which is mounted to the outside of the module. "The temperature at the MLM is comfortable," Russian officials wrote on Telegram (translation provided by Google). They also said there are no changes to operations, experiments or crew exercise periods. The radiator was originally delivered to the space station on the Rassvet module during space shuttle mission STS-132 in 2010. It was later transferred to the Nauka during a Roscosmos spacewalk in April. 'The primary radiator on Nauka is working normally, providing full cooling to the module with no impacts to the crew or to space station operations,' NASA said, adding that it will continue to investigate the cause of the leak. The Nauka leak is the latest in a string of ISS Russian equipment coolant escapes in recent months. As per the Roscosmos, the last two incidents were likely due to micrometeoroid impacts. However, Harvard-Smithsonian space analyst Jonathan McDowell said he suspects there is a "systemic" problem. "You've got three coolant systems leaking -- there's a common thread there. One is whatever, two is a coincidence, three is something systemic," McDowell was quoted as saying to The Guardian. /IANS