WASHINGTON — A propellant leak in a Falcon 9 booster has delayed the launch of a fourth Axiom Space private astronaut mission to the International Space Station.
SpaceX announced late June 10 that it was postponing the scheduled June 11 launch of a Falcon 9 carrying a Crew Dragon spacecraft on the Ax-4 private astronaut mission. The company did not disclose a new launch date.
The company said it needed more time to fix a liquid oxygen leak found in the Falcon 9 booster during inspections following a static-fire test of the booster June 8. “Once complete – and pending Range availability – we will share a new launch date,” the company stated.
Bill Gerstenmaier, vice president of build and flight reliability at SpaceX, mentioned the leak during a pre-launch briefing June 9, but gave no indication then that the leak would delay the launch.
The liquid oxygen leak, he said, was first detected on the booster’s previous flight, a Starlink launch in April. “We discovered we had not fully repaired the booster during refurbishment,” he said. “We didn’t find the leak and didn’t get it corrected.”
He said work was underway to install hardware to mitigate the leak should it continue, which he expected then to be done in time for a June 11 launch. “We’ll be fully ready to go fly.”
Gerstenmaier also said at the briefing that inspections found a problem with the thrust vector control system on one of the engines, requiring technicians to replace components in that system. That work, he said, was not a constraint to launch.
The booster issue is the latest in a series of delays for the Ax-4 mission, once scheduled to launch in the spring. NASA and SpaceX agreed in February to swap the Crew Dragon spacecraft Endurance, originally set to be used on Ax-4, with a new Crew Dragon spacecraft that had been assigned to NASA’s Crew-10 mission because of delays in completing the new Dragon. That allowed Endurance to be used on Crew-10, which launched in March, pushed Ax-4 into late spring.
Final work getting that new, and not yet named, Crew Dragon ready caused the launch to slip from late May to June 8, followed by slips to June 10 and then June 11 because of weather-related issues.
The is no immediate schedule pressure to launch Ax-4. Dana Weigel, NASA ISS program manager, said at the briefing that the station can support launch opportunities through the end of June. After a break to accommodate the departure and arrival of Russian Progress cargo spacecraft as well as lighting conditions, more Ax-4 launch opportunities begin in the second week of July. “There’s plenty of opportunities to fly the vehicle,” she said.
An extended delay, though, would likely impact not just Ax-4 but also Crew-11, the next NASA crew rotation mission scheduled for no earlier than late July. Gerstenmaier noted the same Falcon 9 booster launching Ax-4 will also launch Crew-11.
Ax-4 is Axiom Space’s fourth private astronaut mission, all flown on Crew Dragon spacecraft. Ax-4 is commanded by former NASA astronaut Peggy Whitson, who will be making her fifth flight to the ISS after three NASA long-duration missions and Axiom’s Ax-2 mission in 2023.
Also on board are Indian astronaut Shubhanshu Shukla, who will be the pilot, and mission specialists Sławosz Uznański-Wiśniewski of Poland and Tibor Kapu of Hungary. All three will be the second representing their respective nations to go to orbit.
Ax-4 is scheduled to spend about two weeks at the ISS, performing about 60 science investigations as well as outreach activities. That includes some joint projects between NASA and the Indian space agency ISRO. The scientific research is the most done to date on an Axiom mission.
NASA is currently competing two more private astronaut mission (PAM) opportunities to the ISS. Weigel said one would fly in mid to late 2026 and the other in 2027. She gave no indication that proposed budget cuts, including considerations of reducing the station’s crew size, would affect those plans.
Axiom Space won all four previous PAM opportunities with effectively no competition, but at least one other commercial space station developer, Vast, has signaled its intent to compete for the future PAMs.
“We are intending to compete for the opportunities for PAMs 5 and 6,” Allen Flynt, chief of mission services at Axiom Space, said at the briefing. “All these PAM missions we see as highly valuable and informative for Axiom and our preparation for flying our space station.”
