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March 3rdIn 2021, SpaceX conducted a third high-altitude flight test with one of its Starship prototypesSN10). On this occasion, the prototype managed to reach an apogee of 10 km (6.2 mi), a controlled descent that relied solely on its aerodynamic surfaces (the “belly-flop”), and even managed to land successfully. However, a few minutes after it got stuck on landing, the SN10 exploded on the landing pad.
Meanwhile he SN8 Y SN9 The explosions were attributed to problems that occurred during the restart of the engine, the cause of the SN10 The explosion was not so clear. Fortunately, astrophysicist and YouTube personality Scott Manley (Twitter user @DJSnM) has offered his opinion on what could have caused it. Using SpaceX footage from the SN10 Flight test suggests that a slightly harder landing than anticipated and a ruptured fuel tank were responsible.
In the video, shown above, Manley begins with an observation about the engine flame, where one appeared to be burning more than the others. This became apparent later in the flight when the SN10 It was powered by two motors, one of which emitted a more orange flame than the other. This, according to Manley, could be interpreted as a sign that it was burning more fuel (also known as “fuel rich”).
He attributed this possibility to the first launch attempt made by the ground crews at 09:00 AM CST (07:00 AM PST; 10:00 AM EST). This resulted in an engine abort, where the SN10Automated systems shut down engines because thrust limit (which was set conservatively) was exceeded. In response, the ground crews reset the thrust limit and made a second attempt at 05:14:45 PM CST (03:14:45 PM PST, 06:14:45 PM EST.
After that, the flight continued without incident and the SN10 it reached its maximum altitude approximately 4 minutes and 20 seconds into the flight. The prototype proceeded to successfully hover, shut down all three engines, flip its fuselage, and make a controlled descent using only its fins and aerodynamic surfaces. It was at this juncture, when the engines were restarted and the prototype landed, that Manley pointed out another problem.
For this test, the ground crews were actually hoping to demonstrate that the prototype was capable of landing as the previous two prototypes exploded upon landing. For this reason, they decided to mix things up a bit by firing all three engines at once, then two shut down very quickly, leaving only one to bring the prototype to land.
A few minutes later, after SpaceX had already finished its live coverage, the prototype exploded, leaving many who were still watching asking “what just happened?” As Manley demonstrated by comparing SpaceX and the images collected by LadPadre, the landing was a bit difficult. This was evident from the speed at which it landed and the small bounce that was noticeable once it did.
When the other two Raptor engines shut down, the one that remained on appeared to be spewing a lot of methane as well (as evidenced by the flames around the skirt). To this, Manley offers a theory:
“I think there may be a valve stuck at this point because, of course, after the heavy landing, there were enough things burning on the ground that they needed to employ the water deluge system to help control the situation. So that fire was coming from one of the ground service pipes … You can see that it is initially firing and generating that cryogenic white cloud of very cold gas. And over time, that flame burns out. “
In short, Manley believes that the main problem at this point was the pipeline responsible for charging the rocket with methane fuel (also known as the vehicle’s fuel system). In summary, it stands out that it was do not an engine problem that caused the flame to ignite once SN10 it was on the ground. Looking closely at the images, Manley also identified a problem with the landing legs.
As the SN10 it is lowered onto the platform, three of its legs deployed and locked in place, while the others appear to rotate in and out of position without locking. So, Manley says, the spacecraft appeared to tilt after landing and could have caused structural damage that contributed to the following:
“These legs are a temporary solution. They are designed to be crushed by the force of impact, absorbing energy. And of course, having just three of them instead of six means there’s a lot less infatuation, and that probably contributed to a lot more force being applied to the body. When the smoke cleared, this was largely the ‘Leaning Tower of the Starship’. He had collapsed in the rear with neither of his legs visible. There was no space between the skirt and the floor.“
Using images from LabPadre and NASASpaceflight, Manley was also able to deconstruct the explosion to show what happened. It started with a small puff of smoke billowing from the engine vents, followed by the vehicle’s main oxygen tank splitting in two and releasing an enormous amount of pressure. Soon after, the collecting tank also explodes, releasing additional pressure.
From this, Manley concludes that it was these launches that caused the starship to “jump” off the landing pad. This is similar to what happened during several of the cryogenic load tests with earlier prototypes, where the force of its broken tanks caused the fuselage to “pop”. The resulting release of cryogenic oxygen and methane, plus methane from the fuel system, was caused by the existing fire.
“There is enough pressure in those tanks that when the tank fails, that’s entirely responsible for pushing the vehicle up and causing its destruction,” Manley said. “Fire is kind of a side effect, in this case. It can make the launch a little more aggressive, but a tank failure like that would send the vehicle up and up on its own. “
Other indications are the way in which the explosion was asymmetrical, that is, it happened more on one side, so the fuselage was overturned in the air. The way the fuselage was completely flattened when it hit the ground suggests that the bulkhead between the main methane and the main oxygen tank had failed. Otherwise, he says, “there would have been some kind of gas pressure there and the thing would have gone sideways.”
To sum it up, Manley claims that the explosion was the result of structural damage caused by a harder-than-normal landing, caused by a problem with one of the Raptor engines and the failure of three landing legs. This caused a small fire to break out on landing, followed by the fuel tanks rupturing, sending the fuselage flying while creating a fireball underneath it. In short, it was “pressure-driven”, not an internal explosion.
This type of analysis is no different than what SpaceX engineers are doing right now, which consists of classifying all the mission data to determine the causes (or causes) of the explosion. Naturally, the SpaceX team has a lot more than video footage to go on, but the principle is the same. As always, it is a test to fail, learn and repeat. Only once we are done with everything we can “throw, recover, repeat”.
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