SpaceX CEO Elon Musk had explained what actually happened during the latest extensive Starship mission when a prototype failed. He also revealed the fact that the rocket engines are now set to fuel a future prototype’s debut flight.
SpaceX has carried out the third full-scale Starship prototype’s first cryogenic pressure test by fueling the vehicle’s upper propellant chamber with more than 400 metric tons of liquid nitrogen. For a few hours, the simulant was loaded and discharged several times.
Then, around 07:07 a.m UTC, the liquid oxygen chamber below the methane tank suddenly grooved, and because of gravity, it was pulled to the ground, breaking the rest of the vehicle’s steel shell.
The Failure Was Caused by an Operator Error
Musk has taken it to Twitter to confirm Teslarati’s speculation that as per videos of the issue, an unfortunate test design and operator error, rather than a technical problem of the rocket itself, was most probably the cause of Starship SN3‘s failure.
Simply put, except for the operator error-related issues, Starship’s SN3’s second cryogenic test was a success and should mean no postpones to Starship SN4’s ongoing setting.
The fact that SN3 remained vertical for numerous seconds after its tank bent and probably lost pressure in spite of having a load identical to a fully-equipped Boeing 747 passenger jet shows that the rocket‘s structure is incredibly robust.
Pretty much. Good news is that this was a test configuration error, rather than a design or build mistake. Not enough pressure in the LOX tank ullage to maintain stability with a heavy load in the CH4 tank. This was done with N2.
— Elon Musk (@elonmusk) April 5, 2020
As per Musk’s explanation, it was revealed that the vehicle failed because the liquid oxygen chamber had not been sufficiently pressurized to resist the stress of a methane tank completely loaded with liquid nitrogen. This means that a few people failed to take into account the fact that liquid nitrogen is almost 25 percent heavier than the cryogenic methane it was simulating.
However, although a prototype worth several million dollars and a few months of work was lost, SpaceX is able to continue working on SN4 with confidence. In the same Twitter thread, Musk has revealed three operational Raptors in the same frame, a certain first for the groundbreaking rocket engine.
Raptor Engines to Power SN4
If Starship SN3 had survived its test last week, the agency’s plan was to set up and static fire either one or all three Raptor engines. A successful static fire test would have been followed by a complete Starship debut flight test.
Now, although Musk says SpaceX may still reuse the rocket’s thrust section, the agency’s Starship test plan will focus on SN4, the next complete prototype. It is more probable that SN4 will reuse little to no elements of structure from SN3, but that might end up causing just a few weeks of delays.
Considering a certain assembly step completed on April 4th, Starship SN4 is set to launch in four weeks under the presumption of no enhancements to the speed of production, setting, and testing. However, knowing SpaceX, the rocket could be completely stacked and tested even sooner.
It seems like we’ll have to wait a few weeks to see Starship carrying out another cryogenic proof test, and then, witness the power of one or more Raptor engines installed on it.