A concerning development with an air leak on the International Space Station (ISS) has prompted NASA to indefinitely delay the launch of Axiom Mission 4 for ongoing investigations.

On Thursday, NASA announced that it was working with Russia’s space agency, Roscosmos, to understand a “new pressure signature” in a segment of the Zvezda service module. As a result, NASA and Axiom Space postponed the launch of the company’s fourth private mission to the ISS, which was scheduled for Wednesday, without setting a new date.

The Roscosmos space agency first reported the leak in August 2020. It was found in the Russian Zvezda life support module, which Russia launched to low Earth orbit in July 2000. Since then, the rate at which air is leaking from the Zvezda service module has doubled from one pound a day to a little over two pounds a day, according to a report released in 2024.

This week, NASA revealed that Russian cosmonauts on board the ISS “recently performed inspections of the pressurized module’s interior surfaces, sealed some additional areas of interest, and measured the current leak rate.” Following the inspections, it was revealed that the “segment is now holding pressure,” NASA wrote.

“The postponement of Axiom Mission 4 provides additional time for NASA and Roscosmos to evaluate the situation and determine whether any additional troubleshooting is necessary,” NASA said in its statement. “NASA defers to Roscosmos to answer specific questions about the Zvezda module.”

Last year, NASA elevated the leak to the highest level of risk. At the time, it was reported that NASA and Roscosmos could not agree on the root cause of the leak or a way to fix it. That still appears to be the case today. Although NASA has stressed that the leak poses no immediate threat to the astronauts currently on board, the recent postponement of the Ax-4 mission is worrying; the delay is raising questions about the mission and its international crew.

Peggy Whitson, a former NASA astronaut who holds the national record for the most cumulative days spent in space, is serving as mission commander, joined by pilot Shubhanshu Shukla of India, mission specialist Sławosz Uznański-Wiśniewski of Poland, and mission specialist Tibor Kapu of Hungary. The three countries are sending astronauts to the ISS for the first time in the station’s more than 25-year history—though the timing is less than ideal, with the station grappling with aging hardware.