SpaceX recently rolled out the next generation of Starship boosters to Masseys for testing. However, during a routine ambient-pressure test, the Liquid Oxygen (LOX) tank on Booster 18 ruptured. This incident leaves SpaceX without any Block 3 Boosters available for testing, just 16 days after completing the stacking of Booster 18.
The anomaly occurred during gas system pressure testing, which was being conducted in preparation for structural proof testing. At the time of the test, no propellant was loaded on the vehicle, and the engines had not yet been installed. SpaceX has stated that their teams need time to investigate the cause before they can be confident about what led to the failure.
Booster 18 was rolled out to Masseys on November 20, 2025, with plans to complete its cryogenic proof test campaign ahead of Flight 12. However, in the early morning hours of November 21, the LOX tank ruptured during an ambient-pressure test. This test involved using only nitrogen and oxygen gas to pressurize the tanks and the Composite Overwrapped Pressure Vessels (COPVs).
Based on photos of the damage, it appears that a COPV located at the bottom of one of the larger chines may have exploded during the pressure test. This explosion seems to have triggered a chain reaction that spread up the chine, causing the rest of the COPVs in that chine to fail. The result was a significant rupture in the LOX tank. Remarkably, despite the damage, Booster 18 did not tip over immediately.
Currently, Booster 18 is being held up by the new, larger Liquid Methane (LCH4) transfer tube. It remains unclear how SpaceX will secure the vehicle so that crews can safely return to Masseys. SpaceX faces the challenge of either finding a way to collapse the booster safely and then clean up the debris or using the LR11000 crane at Masseys to stabilize and eventually scrap the vehicle.
If the failure was indeed caused by a COPV, this would not be the first time SpaceX has lost a vehicle due to such an issue. Just five months earlier, on June 18, 2025, SpaceX lost Ship 36 to a COPV explosion during a six-engine static fire attempt. That incident is also the reason why Masseys is still undergoing rebuilding. Alternatively, the rupture could have been caused by a weld failure in the tank wall, but until SpaceX provides more information, the exact cause remains speculative.
The impact of this anomaly on the Starship program is significant. SpaceX currently has no completed flight boosters available and will need to shift focus to Booster 19. However, Booster 19 has not yet begun its stacking process in Mega Bay 1. Even if stacking were to start immediately, and without accounting for investigation and modification time, Booster 19 would not be ready for cryogenic proof testing until at least the end of January.
This is certainly not the start SpaceX had hoped for in the Block 3 era. On the positive side, the failure occurred during proof testing at Masseys rather than during a 33-engine static fire attempt on Pad 2, which could have been far more dangerous.
Regarding the other half of the vehicle pair, Ship 39 is now stacked in Mega Bay 2 and will be outfitted after finishing stacking on November 15, 2025. However, it will be some time before Ship 39 can head to Masseys for testing, as the Ship Cryo Thrust Stand is currently occupied by S39.1.
S39.1 is the Block 3 ship aft test article designed to verify changes to the ship’s aft section. Despite this, Ship 39 will not be needed for a while since Booster 19 has not yet started stacking. The test tank for S39.1 will join B18.1 and B18.3 booster test tanks already at Masseys. These two test tanks have completed a combined total of 17 cryogenic proof tests.
Another consequence of the Booster 18 failure is that SpaceX no longer has a booster available to commission Pad 2. This is a significant issue because all the tank farm equipment must be tested during vehicle loading to ensure it functions correctly. SpaceX might attempt to modify B18.1 to fit inside the launch mount for testing, or they could try to salvage the aft section of Booster 18 and attach some small tanks to it.
If crews cannot find a way to test the new pad in the meantime, SpaceX will have to wait until Booster 19 is ready to be placed on the launch mount. This delay could last a couple of months.
This anomaly follows a series of events in the Starship program. It comes after two successful flight tests following four consecutive failures with Block 2 of Starship. Naturally, this incident will delay Flight 12 indefinitely until SpaceX identifies and resolves the problem and builds a replacement booster for Booster 18.
The image accompanying this report shows Booster 18 with a rupture in its LOX tank after the anomaly during proof testing.