A propellant leak in a Falcon 9 booster has delayed the launch of Axiom Space’s fourth private astronaut mission to the International Space Station (ISS), SpaceX announced late Monday.
The Crew Dragon for the Ax-4 mission atop Falcon 9 rocket on the launch pad at the Kennedy Space Center. Credit: SpaceX
The Ax-4 mission, which had been scheduled for June 11, has been postponed indefinitely while SpaceX works to resolve the issue. According to the company, a liquid oxygen leak was discovered during post-test inspections following a static-fire test on June 8. A new launch date will be announced once repairs are completed and range availability is confirmed.
Bill Gerstenmaier, SpaceX’s vice president of build and flight reliability, had mentioned the leak during a June 9 pre-launch briefing but at the time expressed confidence the issue would be resolved in time for launch. The leak was initially identified during the booster’s previous mission—a Starlink launch in April—but was not fully repaired during refurbishment.
“We didn’t find the leak and didn’t get it corrected,” Gerstenmaier admitted. He noted that new hardware is being installed to mitigate the leak if it persists.
Additionally, inspections uncovered an issue with the thrust vector control system on one of the engines, prompting component replacements. However, SpaceX confirmed that this problem is not a constraint to launch.
This is the latest setback for the Ax-4 mission, which has faced multiple delays. Originally planned for spring, the mission was pushed back when NASA and SpaceX decided in February to swap the Crew Dragon spacecraft “Endurance” for a new, unnamed vehicle. Endurance was reassigned to NASA’s Crew-10 mission, which launched in March, further delaying Ax-4. Additional delays followed in May and June due to final vehicle readiness and poor weather conditions.
Despite the delay, NASA officials have indicated there is no immediate pressure to launch. Dana Weigel, manager of the ISS program at NASA, stated that the station can accommodate launch opportunities through the end of June. After that, a brief window will close to allow for Russian Progress spacecraft activities, but new opportunities will open in the second week of July.
A prolonged delay, however, could affect Crew-11, NASA’s next crew rotation mission scheduled for no earlier than late July, as it is set to use the same Falcon 9 booster as Ax-4.
The Ax-4 mission will be commanded by veteran NASA astronaut Peggy Whitson, making her fifth trip to the ISS. Joining her are Indian astronaut Shubhanshu Shukla (pilot), and mission specialists Sławosz Uznański-Wiśniewski of Poland and Tibor Kapu of Hungary. Each of the three will become the second astronaut from their respective nations to reach space.
The mission is expected to last approximately two weeks and will include around 60 science and outreach activities—the most extensive scientific agenda for any Axiom mission so far. This includes collaborative experiments between NASA and the Indian Space Research Organisation (ISRO).
NASA is currently evaluating proposals for two additional private astronaut missions (PAMs) to the ISS, expected in 2026 and 2027. Axiom Space has flown all four prior PAMs but could face competition from other commercial players like Vast in future bidding rounds.
“All these PAM missions we see as highly valuable and informative for Axiom and our preparation for flying our space station,” said Allen Flynt, Axiom’s chief of mission services.
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