totm nov 2023 SpaceX Discussion Thread

[tater]

12 minutes ago, sevenperforce said:

I'm guessing that debris took out multiple engines as it started to lift off the pad, causing a thrust imbalance, and it took a moment to adjust gimbal enough to bring it back to vertical.

Very possible. The debris was clearly visible well above where I would have expected right at the start.

[sevenperforce]

With the damage to the pad and that end-over-end tumble, this is giving me Ares I vibes to go with the N1 vibes.

[tater]

 

And much more hidden in the dust

Down where the engines were.

[tater]

 

[Minmus Taster]

3 minutes ago, tater said:

 

I have a sneaking suspicion hoppy is not surviving this

[JoeSchmuckatelli]

Wow.

[tater]

Look at the ocean...

Huge splashes ~600m from pad? Farther?

[Kerballlistic07]

33 minutes ago, Minmus Taster said:

I have a sneaking suspicion hoppy is not surviving this

Hoppy did look a little banged up for sure! I was surprised by the amount of debris that flew all over! Concrete I'm assuming?

[Codraroll]

So if I were to dare try a summary, from following the discussion among more knowledgeable people around various discussion forums, this might be the sequence of events that led to the loss of the rocket (not necessarily in order).

Sorry for all the Twitter links, but that's where pictures get posted this soon after the event:

• The launch mount did not withstand the launch forces. It was absolutely trashed by the ignition of the rocket engines. Debris of the concrete pad was sent flying everywhere, smashing up the tank farm, the Starhopper "monument", and cars parked nearby. This shower of crushed concrete might have impacted Superheavy's own engines as well.
• Three engines never ignited. Two more failed shortly after liftoff, followed by a third. One of the six unlit engines ignited again right before the planned stage separation.
• The rocket leaned away from the launch tower and drifted a bit sideways as it lifted off. It's currently unknown if this was deliberate, in a bid to clear the launch tower faster, or a result of the failed engines.
• It is postulated that the quick loss of five engines lowered the rocket's thrust-to-weight ratio to a critically low level, making it too sluggish to reach its intended top speed and altitude. Delta-V loss due to gravity is m/s per second, after all.
• One or both of the rocket's hydraulic power units (HPUs) exploded 30 seconds after launch. The HPUs were presumably damaged by the debris shower from the launch pad.
• The first stage might have gone lower and slower than intended at the time of separation, because so many engines had failed. 
• The rocket then initiated a tumbling motion so that the centrifugal force would separate the Starship upper stage from the Superheavy first stage. Normally, this is just a quick flick, far from a full rotation.
• For some reason, separation did not happen. This could be because the hydraulic system was blown out, so the interstage clamps had no juice to release. Or perhaps the rocket registered it wasn't at the right altitude, velocity, and/or trajectory for stage separation. As demonstrated by the tumble, the two stages held together very firmly.
• EDIT: apparently, this tumble might not have been stage separation after all, just the rocket tipping over as the hydraulics failure finally caused the engines to lose control authority. As it (coincidentally) happened around the right time for separation, it was mistaken for the separation maneuver by the presenters of the stream.
• The rocket tumbled end over end a few times, losing velocity and altitude. This is probably the most Kerbal event of rocketry ever to happen in real life. This is also probably the largest man-made object ever to have been in freefall like that.
• The rocket would have continued to tumble and fall until it impacted the sea, but the Flight Termination System was activated, blowing it up mid-tumble. This way, the rocket is quickly torn apart into smaller pieces that fall almost straight down due to air resistance (instead of a ballistic flight that goes who-knows-where), and all the fuel burns up in the sky instead of on the water surface. Hence, the rocket blowing up was fully intended at that point. The fault wasn't the explosion itself, it was what happened earlier that made the explosion necessary as a form of damage mitigation.

So if we were to link it back to a root cause, the integrity of the launch pad seems a likely culprit. Either it withstood less than expected, or faced more. They will have to give it a complete redesign from the bottom up. Not that re-use would ever be an option given its current condition. Now I wonder what state the launch tower is in.

Edited April 20, 2023 by Codraroll
Tried to remove formatting from copying (I first posted it in another forum).

[RCgothic]

48 minutes ago, Minmus Taster said:

I have a sneaking suspicion hoppy is not surviving this

 

 

[Ultimate Steve]

More from speculation land:

Word on the street is that both hydraulic power units failed, the first one at liftoff and the second one 30s into flight (you can see it exploding). After this, the pressure in the hydraulic system that controlled the engine gimbals gradually fell until the gimbal authority was no longer sufficient for control. The fact that this happened close to stage separation was a coincidence, although without gimbal authority you aren't getting centrifugal separation.

Highly unlikely it would have made near-orbit anyway due to the engine failures, though, it was only going about 500m/s at its peak around 2:30. Need 7.8ish for orbit.

[RCgothic]

1 minute ago, Codraroll said:

So if I were to dare try a summary, from following the discussion among more knowledgeable people around various discussion forums, this might be the sequence of events that led to the loss of the rocket (not necessarily in order).

Sorry for all the Twitter links, but that's where pictures get posted this soon after the event:

•  
• The rocket then initiated a tumbling motion so that the centrifugal force would separate the Starship upper stage from the Superheavy first stage. Normally, this is just a quick flick, far from a full rotation.

 

There's some speculation that with some loss of TVC (the HPUs exploded), together with being lower in the atmosphere and the centre of mass moving forward, that the centre of mass moved forward of the aerodynamic centre, initiating tumbling. That it happened approximately when MECO should have been was coincidence - the engines need to burn longer to correct the low trajectory. Also correcting the trajectory would have required flying at an AoA, exacerbating the assignments instability.

Or if could have been the stage sep flip.

[obney kerman]

Yeesh, that was a lot of issues for one flight. On the one hand, impressive how long the ship stayed in one piece with all that going on, on the other hand... there probably shouldn't have been so many things failing together. Fingers crossed this doesn't delay Artemis 3 by too much...

[Ultimate Steve]

If the critical issue was the hydraulics, that's actually good news as this is a system that they are already phasing out. IIRC the next booster has electric TVC instead of hydraulic TVC, but I might be remembering wrong.

[Minmus Taster]

8 minutes ago, RCgothic said:

 

 

Yeah it's been caved in pretty bad in some places. May have to be scrapped 

[steve9728]

 

- I missed the launch, where's the Starship right now?

-Starship is everywhere

[RCgothic]

Surreal image. After Booster FTS, moments before Starship FTS. Downward facing flap cam.

 

 

[tg626]

I've seen video of flying debris and a shot of the stand where it appears as though the engines eroded a hole in DIRT.

Is there seriously NO pavement, let alone a flame trench, under that launch pad?

[mikegarrison]

3 minutes ago, tg626 said:

I've seen video of flying debris and a shot of the stand where it appears as though the engines eroded a hole in DIRT.

Is there seriously NO pavement, let alone a flame trench, under that launch pad?

Not anymore. (There was pavement, but it didn't survive the launch.)

13 minutes ago, steve9728 said:

 

- I missed the launch, where's the Starship right now?

-Starship is everywhere

That's gonna make SpaceX real popular with the locals if it happens every time.

[Pthigrivi]

Yeah they just need a serious deluge system and trench/diverters that spread the flames out in a star pattern away from stage zero's support columns. They had a lot of concrete rip up on previous engine tests but this was ridiculous. I hope that can be installed without fully replacing the launch base, but either way its gonna take a long time.

Edited April 20, 2023 by Pthigrivi

[s_gamer101]

Was the explosion actually one of the largest man-made non-nuclear explosions or was too much fuel burned before the explosion for that?

[CBase]

Actually I have a feeling stress on launch pad was anormal already. They did spin up quite early and long and then after ignition there was rather some detonation than reflected thrust.

I noticed in the NASA Specaflight video that flames where way faster upwards than transmission from other cam

[sevenperforce]

7 minutes ago, s_gamer101 said:

Was the explosion actually one of the largest man-made non-nuclear explosions or was too much fuel burned before the explosion for that?

Very little of the propellant actually burned up in the explosion. The FTS is designed to "unzip" the tanks and dump them to ambient rather than allowing them to mix and burn.

21 minutes ago, RCgothic said:

Surreal image. After Booster FTS, moments before Starship FTS. Downward facing flap cam.

 

 

Absolutely amazing.

[obney kerman]

3 minutes ago, s_gamer101 said:

Was the explosion actually one of the largest man-made non-nuclear explosions or was too much fuel burned before the explosion for that?

The N1 was biggest because it was on the pad and fully fueled when it exploded. I think between four minutes of thrust and how it looked like the LOX supply was going down a bit too quickly on the interface it was more of a Challenger-esque aerodynamic breakup. If you look closely at the videos of it you can even see what looks like unburned fuel spilling out as it breaks apart.

 

[CBase]

After some slow motions thrust below pad seamed to build up normal, the delay between cameras was just very high. However there are flames coming from above, which might have been HPU