SpaceX foundation slab pulverised 11

[saikee119]

The above photo was from a youtube video showing the reinforced concrete supporting structure of the SpaceX rocket before and after the yesterday's launch when it exploded 4 minutes into the flight.

It appears the RC slab was flush as one level prior to the launch but now has the ground beams exposed. The video also claimed there were concrete fragments flying all over the place as shrapnel damaging some fuel and water tanks.

There seem to be at least the following issues in play:-

(1) The "disappeared" reinforced concrete slab was totally unsuitable for its purpose. I do not know if it was reinforced or not but it would have been criminal if it wasn't.
(2) The reinforced concrete columns and ground beams show little damage. This would suggest the reinforced concrete in adequate dimension could be the suitable material for the structure including the slab if adequately shield from the high temperature heat.
(3) Had any of the RC column or ground beam failed during the last launch the supporting structure might not have remained static then the rocket could have shot off at an angle other than vertically upward. Consequently a huge disaster could occur if the rocket hit the population with the amount of fuel it carried.

 

[FacEngrPE]

https://www.newsweek.com/spacex-starship-launch-destruction-video-1795989[/URL]]"I believe the launch went as expected," Balderas (spaceX) said. . . . There was a huge 20-foot deep crater left underneath the launch mount," he said. "I'm sure there will be some new designs coming out to keep the 33 raptor engines from annihilating the concrete foundation. There was also some damage to the fuel farm which I'm sure will need to be repaired and possibly redesigned."

Some good videos showing the concrete chunks flying past the camera in the referenced web page..
jet is?
My guess is that the concrete will need to be protected by some sort of hard refractory brick. Does anyone know what the stagnation temperature in the center of merlin engine? That is the minimum exposure temperature requirement in a flame chute with a turn of this sort.

 

[Eufalconimorph]

Scott Manley's analysis is good. Rapid unscheduled digging threw concrete around, which destroyed several engines. The others that failed may have also been damaged, and just took longer to completely stop working. The rocket lost (at least some) attitude control, was too low to separate, and eventually the flight termination system blew it up.

There's a good picture of the concrete having been stripped completely away from the rebar. They definitely need a flame diverter.

 

[FacEngrPE]

Musk was quoted today as indicating the pad concrete was made of Fondag(R)

https://www.imerys.com/product-ranges/fondag[/URL]]Fondag concrete shows good workability followed by a rapid hardening and allows users to resume operations as early as 8 to 10 hours after application. It is resistant to temperatures from -180°C to +1100°C and thermal shocks, as well as corrosion caused by sulfates, oils, industrial waste, and several chemicals and acids.

This is a new product to me, it seems to have characteristics useful for this application, but as a main engine flame target it needs to resist stagnation temperature which must be much higher than 1100C, the field test proves it is not enough.

Plans are starting to emerge (video links). Looks like significant construction effort.

https://youtu.be/YJuqyZVQzTc

https://youtu.be/7NePqKvLpiY

 

[hokie66]

So high tech failed due to failure of low tech stuff?

 

[FacEngrPE]

Fondag concrete may only be made from rock, but it is not exactly low tech either. Refractory materials as a group are a fascinating engineering subject in themselves. Lots of ways to make incorrect selections.
The ceramic nozzle of the Merlin engine is one example of a high tech ceramic refractory. The nozzle material likely would not work as a flame target.
Fondag is from the general class of chemical cure castable alumna based materials.
It is the out of sight edge case of Temperature, thermal shock, mechanical shock, jet velocity, and water impingement that makes it not work.
I suspect most flame chutes protect the refractory material from encountering the hot jet by ensuring there is a layer of steam between them. Then the refectory only needs to handle radiant energy from the jet.

 

[saikee119]

I would guard against the use of the proprietary "Fondag concrete" as a structural material to withstand 1100C. It appears its property to withstand 1100C may as a refractory shield and not necessary as a structural element to resist compressive load and abrasion.

In ACI 349M-06 for Nuclear safety-related structures it was stated
6.3.15 All piping containing liquid, gas, or vapor pressure in excess of 1.4 MPa above atmospheric pressure or temperature in excess of 66 °C shall be sleeved, insulated, or otherwise separated from the concrete and/or cooled to limit concrete stresses to allowable design strength and to limit concrete temperatures to the following:

(a) For normal operation or any other long-term period, the temperatures shall not exceed 66 °C, except for local areas that are allowed to have increased temperatures not to exceed 93 °C;

(b) During an accident or for any other short-term interruption, the temperatures shall not exceed 177 °C for the interior surface. However, local areas are allowed to reach 343 °C from fluid jets in the event of a pipe failure;

(c) Higher temperatures than given in Items (a) and (b) may be allowed in the concrete if tests are provided to evaluate the reduction in strength and this reduction is applied to the design strength. Evidence shall also be provided that verifies that the increased temperatures do not cause deterioration of the concrete with or in the absence of applied loads.


Thus in a nuclear melt down if the concrete were to remain as a structural element the temperature permitted is less than 343C. Fondag concrete may be applied as a shield over and above the structural concrete but can it bond to it under severe pressure and heat without being blown off is a key design consideration too.

 

[dold]

Does anyone know what the stagnation temperature in the center of merlin engine

This vehicle was using 33 Raptor engines, not Merlins.

 

[MJCronin]

Early in the rocket design phase, Elon Musk wisely vetoed the "33 MERLIN Engine " concept ...

Too much interference with the many propellers....

https://en.wikipedia.org/wiki/Rolls-Royce_Merlin

MJCronin
Sr. Process Engineer

 

[Jedidad]

"...(3) Had any of the RC column or ground beam failed during the last launch the supporting structure might not have remained static then the rocket could have shot off at an angle other than vertically upward. Consequently a huge disaster could occur if the rocket hit the population with the amount of fuel it carried..."

They would have activated the Flight Termination System to blow it up.

Close up in 4k, Orbital Launch Pad, SpaceX Starbase, Boca Chica, TX, April 22, 2023
Link

 

[Murph 9000]

They would have activated the Flight Termination System to blow it up.

Yeah, that combined with the normal practice of having the launch site safely separated from populated areas makes that risk extremely low (other than to people and structures within the launch complex and immediate industrial areas). Additionally, the initial thrust:weight is not all that huge; it doesn't accelerate like a firework or a small to medium sized military rocket/missile.

I also think it's reasonably unlikely that the support structure would have significantly failed in the very brief period where the engines were at full thrust and the weight was still on the structure.

 

[hokie66]

Sorry, Murph, but that is highly likely.

 

[Murph 9000]

@hokie66, I could be wrong. Here's my rationale. The missing concrete did not just instantly vaporise when the thrust was first applied, therefore the ability of the structure to support the rocket did not instantly diminish to a critical level. Yes, damage would start to occur as soon as thrust was applied, but it's an ablative process which took time to produce the end result we saw in pictures of the damaged structure. So, the critical moments are where the structure is still supporting the rocket and significant thrust is being generated. Once the engines approach full thrust, the structure is no longer supporting the rocket and failure of the structure can no longer cause the rocket to cant away from vertical. There should be a relatively small window where there's a high rate of ablation and the weight is still on the structure. The ablation would continue for some time after the rocket had lifted off the structure, so a lot of the observed damage should have been after the point where failure would take the rocket off vertical.

There is a second argument that debris getting thrown back up into the base of the rocket could have damaged it to the extent where the remaining engines caused it to accelerate in an unintended direction. That's a real risk, and it appears that there may have been some engine damage from debris generated on the pad. In my rationale above, I'm only looking at the ability of the structure to support the rocket.

 

[dold]

There is a second argument that debris getting thrown back up into the base of the rocket could have damaged it to the extent where the remaining engines caused it to accelerate in an unintended direction

This is what a lot of the videos I've browsed seem to agree with: debris appears to have struck the Hydraulic Power Unit (HPU) and one or two or more of the engines. The damage to the HPU is (one of?) the main reason that stage separation did not occur later in the flight. Loss of the HPU would also cause the loss of thrust vectoring capabilities.

Here's a solid video on the damage to the rocket: [URL unfurl="true"]https://www.youtube.com/watch?v=w8q24QLXixo[/url]

 

[MJCronin]

doid, et al....

The YOUTUBE video that you reference is very informative ...

I find it particularly telling that two adjacent Raptor engines were not functioning within a few seconds after takeoff.

This is significant evidence (IMHO) for a "common-cause" mechanical failure .... like, ..... ummmmmm.....ohhhh .... say a big rock kicked up ...

Another video of the damage ...

https://www.youtube.com/watch?v=bm3ILLwhGSQ

MJCronin
Sr. Process Engineer

 

[EdStainless]

I have walked in the flame diversion trenches at pad 34A. (after a launch)
The amount of water that they can pour through them is incredible.
The exhaust should never directly impinge on the concrete.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[saikee119]

According to the simple Newton's law I would have expected the vertical thrust action to send off SpaceX could only materialise when there was an equal and opposition reaction provided by the apron concrete slab. This apron concrete slab has been pulverised and the soil underneath was also partially blown away and scoured. Did the site provide a reaction condition far from perfect for sending off the SpaceX?

There is a rumour that FAA has stopped the SpaceX until the problem of the supporting structure has been fixed to their satisfaction.

 

[Murph 9000]

There might be some sort of additional ground effect while on the pad, but the reaction force for a rocket in flight comes from the mass of expanding gas being pushed out of the nozzles. At least that's my limited understanding and putting it simply. I'm happy to be corrected by physics PhDs and rocket scientists. In a hypothetical scenario where the rocket was above a functionally infinite void while at rest on its mount (i.e. no possibility of a reaction force from something solid beneath it), it would be possible for it to ignite, lift off from the mount, and reach orbit; provided that thrust:weight was > 1.0 (TWR, for the Kerbonauts out there), and that it had sufficient delta-V in its ascent stages.

 

[dold]

There is a rumour that FAA has stopped the SpaceX until the problem of the supporting structure has been fixed to their satisfaction.

Possibly that, but I heard the reason also includes unexpected environmental impacts - wildlife habitats and also the amount of debris/dust that ended up covering peoples cars/houses/bodies/etc, as well as the noise aspect. These are all factors that would have been discussed and evaluated during environmental assessments and the like during the FAA approval process.

 

[bones206]

This photo has been floating around the internet.