SpaceX’s Ax-4 Mission to ISS Delayed After Propellant Leak Identified – by Frederic Eger – – Photo: The SpaceX Falcon 9 rocket and Crew Dragon capsule that will fly the Ax-4 private astronaut mission stand on the pad at NASA’s Kennedy Space Center in Florida. (Image credit: SpaceX) -The four-person mission was scheduled to launch on June 11 from NASA’s Kennedy Space Center in Florida. However, the launch has been postponed to allow additional time for SpaceX teams to repair the leak, which is liquid oxygen, one of the two propellants used by the Falcon 9’s Merlin engines. The other propellant is RP-1, a rocket-grade kerosene.

“On Saturday, (…) during the static fire [test] (…) we found a locks leak that we previously had seen on this booster during its entry on its last mission and discovered that we had not fully repaired the booster during refurbishment.(…)” 

William Gestmeier, 
Build & Flight Reliability,
Vice-President SpaceX

SpaceX noticed the leak after static-firing the rocket’s first stage on June 8. Static fires are common prelaunch tests where a rocket’s engines are briefly ignited while the booster is anchored to the pad. Bill Gerstenmaier, SpaceX’s vice president of build and flight reliability, discussed the leak during a press conference on Monday (June 9) after Ax-4’s launch readiness review.
SpaceX discovered that they had not fully repaired the booster during refurbishment or didn’t find the leak and didn’t get it corrected. Gerstenmaier said that SpaceX was still troubleshooting the leak, but expressed confidence that the issue wouldn’t prevent an on-time liftoff. “We’re installing a purge that will essentially mitigate the leak, if it still continues, if we see it on launch day,” he said. “So we will be fully ready to go fly.”
Ax-4 will be the fourth astronaut mission to the ISS organized by Houston company Axiom Space. It will be commanded by Peggy Whitson, a record-breaking former NASA astronaut who is now Axiom’s director of human spaceflight. The other crewmembers are pilot Shubhanshu Shukla of India; mission specialist Sławosz Uznański-Wiśniewski of Poland and the European Space Agency; and Hungarian mission specialist Tibor Kapu. No astronaut from any of these three countries has ever visited the ISS before.
The Ax-4 astronauts will spend about two weeks living and working aboard the orbiting lab, performing about 60 different science experiments. They will then return to Earth with a splashdown in the Pacific Ocean.