SpaceX says it has identified and fixed the problem that caused its Falcon 9 rocket to fail during a launch earlier this month. The failure occurred on July 11 when a Falcon 9 carried 20 Starlink broadband satellites towards low Earth orbit, but a leak of liquid oxygen in the upper stage prevented it from conducting an orbit-raising burn as planned. This resulted in the satellites being deployed too low and burning up in the atmosphere.
The cause of the leak was a cracked sense line for a pressure sensor attached to the vehicle’s oxygen system. The crack occurred due to fatigue caused by high loading from engine vibration and looseness in the clamp that normally constrains the line.
The upper stage’s Merlin engine performed its first burn as planned, but the leak prevented it from conducting a second burn designed to circularize its orbit ahead of Starlink satellite deployment. This led to excessive cooling of engine components, resulting in a hard start rather than a controlled burn, which damaged the engine hardware and caused the upper stage to lose attitude control.
Although all 20 satellites were deployed, they did not stay in orbit long. SpaceX has taken action to prevent the recurrence of the anomaly by removing the failed sense line and sensor on the second-stage engine for near-term Falcon launches.
The company has also submitted its mishap report to the FAA and is poised to rapidly return to flight as soon as Saturday, July 27.
Source: https://www.space.com/spacex-finds-cause-falcon-9-rocket-failure