Ahead of the fourth test flight of the Starship rocket, scheduled to take place around June 5, SpaceX explained what happened during third launch attempt in mid-March.
The Starship then gained altitude after successfully separating from the Super Heavy booster stage, but failed to flood the Gulf of Mexico. Although the launch vehicle fired 13 Raptor engines, six of them began to shut down mid-flight: "The launch vehicle continued to descend until it attempted to land, but the six engines that shut down during the early acceleration phase were shut down . As a result, seven engines were commanded to start, and two successfully achieved ignition of the main stage. The launch vehicle had less than expected thrust on landing and lost contact with it at an altitude of approximately 462 meters above the Gulf of Mexico, just under seven minutes into the flight.
Flight data analysis showed that the most likely cause of the early shutdown of the afterburner mode was a clogging of the ongoing filter through which liquid oxygen is fed to the engines. This resulted in a loss of pressure at the inlet to the engines' oxygen turbopumps.
SpaceX had already faced similar problems during the second flight of Starship and made changes to the equipment. Engineers have now decided to introduce additional equipment inside the oxygen tanks to further improve fuel filtration capabilities. They will also make additional hardware and software changes to improve the reliability of launching Raptor engines under landing conditions.
After entering orbit, Starship also had a number of problems. During the coasting phase, when the Raptor engines were not operating, the missile's orientation was determined by the roll control engines. However, it appears that the roll control valves were clogged. As a result, the Starship did not attempt to restart the Raptor engine as originally planned, and entered the dense parts of the atmosphere without being able to maintain a given orientation. As a result, not only the heat shield, but also other parts of the rocket were affected by the plasma. Telemetry stopped transmitting to Earth at an altitude of approximately 65 km at 49 minutes into the flight. SpaceX will now add more thrusters to improve attitude control redundancy, and upgrade its lock-up stability enhancement hardware.
Finally, the Super Heavy will ditch the post-burnback hot stage adapter to reduce booster mass during final flight .
SpaceX says it will now shift its focus from going into orbit to demonstrating the ability to return and reuse the Starship and Super Heavy. The company needs to demonstrate a successful soft landing of Super Heavy and Starship during controlled reentry, especially at the point of maximum heating.