Thread by @mcrs987

Starship's 7th flight test resulted in an untimely demise of the Starship upper stage.

Through days of analysis and consulting several people on the matter I believe I have pieced together the majority of the timeline of exactly what happened to @SpaceX's Starship S33.

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This thread will cover the timeline in a play-by-play manner.

There's a chance this is completely wrong, however, this is the best conclusion that can be made with available information

- THE FUEL LEAK

The most likely for the fuel leak to have started would have been in the transfer tube between the Methane downcomer and the E1 engine fuel powerhead.

This transfer tube has been observed in previous flights to have been a major problem point.

Another noted choke point that has leaked fuel in the past was the Main Fuel Valve on the raptors themselves however I do not believe this is what the source of the fuel leak was because of the manner in which the sea level engines are nestled below the firewall.

It is possible that there was a defect or some other unstable area within the liner of this transfer tube (as it has flexible sections to accommodate engine gimbal) that caused the leak to form in the first place. (picture is a cross section of a similar cryogenic flex line)

The leak itself likely began to form just after the T+5 minute mark. Both eyewitness account from the ground (describing mild disturbance in the plume at this time) and the rate of fuel consumption coincide at the same time, seemingly insinuating something began there.

- E1 SHUTDOWN

About two more minutes go by where this fuel leak is allowed to develop and grow unrestricted.

At T+7:39, Engine E1 shuts down. If the previous mention of the fuel leak starting very early and developing further is correct, then the pressure inside of the

transfer tube would have dropped below the critical pressure required for nominal operation of the fuel turbopump. This would cause caviation bubbles to form within the inducer, destroying the delicate turbomachinery and causing the external housing to blow out.

- THE FIRE
This engine failure would effectively act as an ignition source for the fuel that has been pouring out of the transfer tube for the past minute or two.

The violent failure of E1 would have also caused damage to itself, allowing enough oxygen to be released to burn.

The pressure within the engine bay cavity would rise rapidly as densified liquid propellant is burned and turns into a gaseous state. The small vents on the exterior of the ship (in combination with the openings at the aft flap hinges) were not designed to handle such a drastic

overpressure within the engine bay, so they were completely inadequate in aiding in the extinguishing of the fire.
Less than 15 seconds after the potential ignition of the fire, it is already visible within aft flap hinges. This fire was extremely violent.

- SUBSEQUENT ENGINE FAILURES
This fire likely burned through several subsystems within the engine bay, potentially causing each engine to one-by-one destabilize and shut down on via their own controllers. It is likely that each subsequent engine failed on similar terms.

Loss Of Signal occurs at T+8:26. It's not entirely clear what caused this, however, there are two running theories both ending in the same way.

(This bit is highly speculative)

A- Engine bay fire reached the ship's high voltage battery and disabled it, causing a full vehicle power loss.
B- Engine E5 shuts down in an off-nominal manner and disables the ship's high voltage battery (said battery is directly above E5), also causing a full power loss

In either scenario, the most probable outcome for the cause of LOS would be both flight computers shutting down simultaneously. This is why the Flight termination system did not detonate here. Unlike on S25, where both of these computers remained active but were unable to

communicate with eachother, on Ship 33 the entire system is shut down.

The FTS has it's own batteries, antennas, computers etc and is unaffected by such a power loss

No matter what caused LOS itself the outcome is the same, the vehicle now on an unpowered coast for a little less than 3 minutes. The ship reaches an estimated apogee of about 152 kilometers

At T+11:22, Starship breaks up 76km over the northern Caribbean.

I am inclined to believe that the breakup was induced by the FTS as a range violation rule. Through figuring out the locations of about half a dozen videos of the breakup I was able to estimate the RUD position to a 44 square kilometer area.

Overlaying the hazard zones and debris response areas shows something interesting. The position of breakup runs mere kilometers away from the boundaries of these zones.

Considering the ship was well within the atmosphere falling back, it is likely that the programmed

flight corridor below 100km stopped at the end of one airspace zone, which is where the DRA (in pink) begins.

From there the ship breaks up into two major components.

These two globules of debris take very different trajectories on the way down. There's a few of these very special photos directly downrange of the entry. You can see the nosecone globule headed straight at the camera while the aft section arcs over to the left (to the south)

Sonic booms of the debris was picked up around this time, where you can also clearly see two peaks as each of the two debris globules come down to subsonic at different times

Now the topic that has a weird amount of controversy; debris exiting the established hazard zones.

The end of the entry of the aft section globule was caught on the San Juan Doppler Radar. This streak is NOT an anomaly or an artifact, each reading has a measured

altitude and it coincides exactly as the entry of the debris would be expected to fall under.

This debris was still airborne outside BOTH the NOTAMs & MISB, as WELL as the contingency Debris Response Areas.

This thread is more of a basic summary of my findings. If you have any questions, I would love to talk on specific details that you may be interested in

Also, I’ve published a video version of this with more information and better visual examples, which can be found here;