To update: Yesterday (March 9th) Elon Musk shared the reason for the explosion via Twitter. According to Musk, the problem was due to the one Raptor engine that was used to slow the SN10 down before landing.
“The SN10 engine had little thrust (likely) due to the partial uptake of helium from the fuel rail,” he tweeted. “Impact of 10 m / s bruised legs and part of the skirt. Several corrections are in progress for SN11. “
On March 3, 2021, SpaceX conducted a third high-altitude flight test with one of its Starship prototypes (SN10). This time the prototype managed to peak 10 km, a controlled descent that relied only on its aerodynamic surfaces (the “belly flop”), and even managed to land successfully. A few minutes after the landing got stuck, the SN10 exploded on the landing pad.
While the SN8 and SN9 explosions were due to problems encountered during the re-ignition of the engine, the cause of the SN10 explosion was not so clear. Fortunately, astrophysicist and Youtube personality Scott Manley (Twitter handle @DJSnM) has offered his opinion on what could have caused it. Using the SpaceX footage of the SN10 flight test, he suggests that a slightly harder than intended landing and a fuel tank rupture were responsible.
In the video shown above, Manley begins an observation regarding the engine flame, where one appeared to burn hotter than the other. This became apparent later in flight when the SN10 was running on two engines, one of which emitted a flame that was more orange than the other. According to Manley, this could be interpreted as a sign that more fuel was being burned (also known as “fuel-rich”).
He attributed this possibility to the ground crews first attempt to take off at 9:00 a.m. CST (7:00 a.m. PST; 10:00 a.m. EST). This led to an engine crash, in which the automated systems of the SN10 switched off the engines because the (conservatively set) thrust limit was exceeded. In response, the ground teams reset the thrust limit and made a second attempt at 5:14:45 p.m. CST (3:14:45 p.m. PST, 6:14:45 p.m. EST).
Thereafter, the flight continued without incident and the SN10 reached its maximum altitude approximately 4 minutes and 20 seconds after the start of the flight. The prototype successfully floated, turned off all three engines, flipped the hull and performed a controlled descent using only its fins and aerodynamic surfaces. At that point, when the engines re-ignited and the prototype landed, Manley pointed out another problem.
For this test, the ground teams had really hoped to show that the prototype could land, as the previous two prototypes exploded on touchdown. Because of this, they decided to mess things up a little by firing all three engines at once, then two shut down very quickly, leaving only one to bring in the prototype for a landing.
Footage showing the orange flame emitted from one of the Raptor’s engines in flight. Image Credit: SpaceX
A few minutes later, after SpaceX had finished its live coverage, the prototype exploded and many who were still watching asked, “What just happened ?!” As Manley demonstrated by comparing SpaceX and footage collected by LadPadre, the landing was a bit rough. This could be seen in the speed at which it touched down and in the small jump that was once noticeable.
When the other two Raptor engines shut down, the one that remained lit also appeared to be venting a lot of methane (as the flames around the skirt indicate). Manley offers a theory:
“I think a valve could get stuck at this point because – of course – enough material burned on the ground after the heavy landing for us to use the flood system to keep the situation under control. So the fire was coming from one of the ground pipes … you can see that it initially shoots, creating this cryogenic white cloud of very cold gas. And over time this flame burns into it. “
In short, Manley believes the main problem at this point was the installation responsible for loading the rocket with methane fuel (aka the vehicle fuel system). In short, he emphasizes that once the SN10 was on the ground, it wasn’t an engine problem that caused the flame to go up. Upon closer inspection of the footage, Manley also identified a problem with the landing legs.
The three Raptor engines are re-ignited before landing. Image Credit: SpaceX
As the SN10 lowers onto the pad, three of its legs extend and lock into place, while the others pivot in and out of position with seemingly no locking. Because of this, Manley said, the spacecraft appeared to lean upon landing and could have caused structural damage that contributed to what followed:
“These legs are a temporary solution. They are designed to be crushed by the force of impact and absorb the energy. And of course, having only three instead of six means there’s a lot less crushing, and that probably contributed to a lot more force being put on the body. When the smoke cleared, this was the “Leaning Tower of the Spaceship”. It had collapsed at the back with no legs visible. There was no space between the rock and the floor. “
Using footage from LabPadre and NASASpaceflight, Manley was also able to deconstruct the explosion to show what happened. It started with a small cloud of smoke from the engine vents, followed by splitting the vehicle’s main oxygen tank into two parts and releasing an enormous amount of pressure. Shortly thereafter, the expansion tank also bursts, releasing additional pressure.
From this, Manley concludes that it was these publications that caused the spaceship to “jump” from the landing site. This is similar to what happened in several cryogenic stress tests on previous prototypes, where the force of their broken tanks made the hull “jump”. The resulting release of cryogenic oxygen and methane, as well as the methane derived from the fuel system, was ignited by the existing fire.
The explosion, minutes after touching down. Image Credit: LabPadre
“There is enough pressure in these tanks that, if the tank fails, is entirely responsible for pushing the vehicle up and causing its destruction,” said Manley. “The fire in this case is a kind of side effect. It might make the start a little more aggressive, but such a tank failure would send the vehicle up and the vehicle up on its own. “
Other clues include the way the explosion was asymmetrical – meaning more on one side – which caused the hull to tip over in midair. The way the hull was completely flattened at the time of impact suggests that the partition between the main methane and main oxygen tank had failed. Otherwise, he claims, “There would have been some kind of gas pressure there and the thing would have gone sideways.”
In summary, Manley claims the explosion was the result of structural damage caused by a harder-than-normal landing caused by a problem with one of the Raptor’s engines and the failure of three landing legs. This resulted in a small fire breaking out on landing, followed by the fuel tanks bursting, causing the fuselage to fly and creating a ball of fire underneath. In short, it was “pressure driven,” not an internal explosion.
This type of analysis is no different from what SpaceX engineers are currently doing. In doing so, all mission data is sorted to determine the causes (or causes) of the explosion. Of course the SpaceX team has a lot more to offer than just video, but the principle is the same. As always, it’s a test of failure, learning, and repeating. Only when we are done with all of this can we “start, restore, repeat”.
Like this:
Loading…
Comments are closed.