SpaceX explains why two Starships exploded

SpaceX explained the cause of the Starship rocket explosions during its ninth test flight in late May and during testing at the launch pad. Elon Musk's company introduced the necessary modifications, and the FAAgranted clearance for the tenth test flight, scheduled for August 24.

Cause of explosion during IFT-9

During the ninth flight on May 27 (May 28 in Italy), everything worked perfectly until the separation of the two stages. For the reentry phase of the lower stage (Super Heavy 14-2), an angle of approximately 17° had been chosen to evaluate hardware limitations. After the ignition of 12 of the 13 Raptor engines (approximately 382 seconds after launch), an energetic event ( explosion ) occurred at an altitude of approximately 1 km.

Due to the high reentry angle, the force applied to the booster structure increased. This caused a fuel transfer pipe to rupture , resulting in the mixing of methane and liquid oxygen, and the subsequent explosion. A lower reentry angle will be chosen for future tests to reduce aerodynamic forces and thus the likelihood of structural failure.

The upper stage (Ship 35) continued its flight along its planned trajectory. Approximately three minutes after ignition of the six Raptor engines, sensors detected a decrease in pressure in the main tank and a decrease in pressure in the nose section. The pressure drop was compensated by Ship 35's systems, allowing the rocket to reach its planned speed and subsequently shut down the engines.

The high pressure, combined with venting (gas release), caused a significant loss of attitude, which continued until venting automatically deactivated. This, however, prevented the hatch from opening to release the dummy Starlink satellites.

The attitude error was reduced by the reaction control thrusters until the venting was expected to re-engage. Approximately 40 seconds later, onboard cameras showed liquid methane entering the forward section. This triggered the vehicle's automatic passivation controls. The single engine failed to ignite as planned, and Ship 35 vented all its remaining propellant into space.

Ship 35 reentered Earth's atmosphere in a non-nominal attitude. It then exploded approximately 46 minutes after launch, at an altitude of approximately 59 kilometers. The most likely cause was a failure of the main tank pressurization system diffuser. Pre-flight analysis did not reveal the failure, but SpaceX engineers were able to recreate it using flight conditions during testing at the McGregor facility in Texas. The diffuser has been redesigned to reduce stress on the structure during future flights.

Cause of explosion on Ship 36

Ship 36 exploded during the static fire test on June 18 , specifically during propellant loading. As already specified at the end of the preliminary analysis, the rupture of a tank called a COPV (Composite Overwrapped Pressure Vessel) containing nitrogen gas caused the structural failure and subsequent mixing of the propellant. COPVs on future flights will operate at reduced pressure.

Tenth flight objectives

SpaceX has scheduled its tenth test flight (IFT-10) for 6:30 p.m. on August 24 (1:30 a.m. on August 25). It will use Super Heavy Booster 18 (first stage) and Ship 37 (second stage). The objectives for Ship 37 are the same as those for Ship 35: release eight dummy Starlink satellites, fire an engine in space, and splashdown in the Indian Ocean.

There are two new features for Super Heavy Booster 18 compared to its ninth flight. Capture by the launch tower's "arms" is not planned, but the lower stage will fall into the Atlantic Ocean. During reentry, one of the three central engines will also be shut down to test the feasibility of a two-engine landing.