SpaceX's next private astronaut launch to ISS, Ax-4, pushed back to June 10 Standing down from tomorrow’s Falcon 9 launch of Ax-4 to the @Space_Station to allow additional time for SpaceX teams to repair the LOx leak identified during post static fire booster inspections. Once complete – and pending Range availability – we will share a new launch date pic.twitter.com/FwRc8k2Bc0June 11, 2025 LOx is liquid oxygen, one of the two propellants used by the Falcon 9's Merlin engines. The other is RP-1, a rocket-grade kerosene. As SpaceX's post mentioned, the company noticed the LOx leak after static-firing the rocket's first stage, an activity that took place on Sunday (June 8). Static fires are common prelaunch tests in which 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) that was held after Ax-4's launch readiness review. This Falcon 9 first stage has one flight under its belt, and the leak was also seen on that mission, during its reentry to Earth's atmosphere, Gerstenmaier said. Get the Space.com Newsletter