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SpaceX foundation slab pulverised
11

SpaceX foundation slab pulverised

SpaceX foundation slab pulverised

(OP)


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.

RE: SpaceX foundation slab pulverised

Quote (https://www.newsweek.com/spacex-starship-launch-de...)

"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.

RE: SpaceX foundation slab pulverised

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.

RE: SpaceX foundation slab pulverised

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

Quote (https://www.imerys.com/product-ranges/fondag)

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

RE: SpaceX foundation slab pulverised

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

RE: SpaceX foundation slab pulverised

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.

RE: SpaceX foundation slab pulverised

(OP)
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.

RE: SpaceX foundation slab pulverised

Quote (FacEngrPE)

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

This vehicle was using 33 Raptor engines, not Merlins.

RE: SpaceX foundation slab pulverised

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

RE: SpaceX foundation slab pulverised

2
"...(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

RE: SpaceX foundation slab pulverised

Quote (Jedidad)

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.

RE: SpaceX foundation slab pulverised

Sorry, Murph, but that is highly likely.

RE: SpaceX foundation slab pulverised

@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.

RE: SpaceX foundation slab pulverised

Quote (Murph)

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: https://www.youtube.com/watch?v=w8q24QLXixo

RE: SpaceX foundation slab pulverised

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

RE: SpaceX foundation slab pulverised

2
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

RE: SpaceX foundation slab pulverised

(OP)
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.

RE: SpaceX foundation slab pulverised

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.

RE: SpaceX foundation slab pulverised

Quote (saikee119)

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.

RE: SpaceX foundation slab pulverised

This photo has been floating around the internet.

RE: SpaceX foundation slab pulverised

The bare rebar cage for the grade beam...wow...

RE: SpaceX foundation slab pulverised

I read somewhere that a flame diverter system was intended to be built, but the permitting process through the army corps of engineers would have significantly delayed the launch. I'm curious how other regulatory bodies allowed this launch to proceed, knowing that this critical safety system was left out.

This is all unverified btw. I've just skimmed a few articles here and there, so take it with a grain of salt.

RE: SpaceX foundation slab pulverised

If I were the regulator (which I'm not and never will be), I'd be wanting answers about the adequacy of the Flight Termination System before authorising another flight.

RE: SpaceX foundation slab pulverised

Well, didn't Musk say from the beginning it would be a BFR . . .surprise

RE: SpaceX foundation slab pulverised

Saikee…

"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."

That's not how rockets work. Rockets generate their own thrust and do not need a launch pad to generate the reaction (or an atmosphere, as the rocket deniers claim). As Murph said, "the reaction force for a rocket in flight comes from the mass of expanding gas being pushed out of the nozzles."

Think about it: once the rocket lifts off, the only "connection" between the launch pad and the rocket is a stream of outbound, unconfined, compressible fluid (exhaust gas) and you will not be able to transmit a thrust force through that exhaust gas. And, as the rocket climbs, that "connection" becomes more and more tenuous before it vanishes completely.

Here is an easy way to understand how rockets generate thrust, although the analogy is not complete. We will use a spherical balloon to mimic the combustion chamber in a rocket. First, blow up the balloon and hold the nozzle closed. Next, make a free-body diagram of internal air pressure inside the balloon. Obviously, the vector forces completely balance around the entire sphere, so there is no net thrust in any direction and thus no acceleration. For this simple example, we are ignoring the external air pressure (because it also balances and because there is none in space) the tension forces in the surface of the balloon (because they also balance), and the mass of the balloon and the enclosed air. Finally, open the nozzle of the balloon and redraw the free-body diagram. As you can see, a small area of the balloon's surface, opposite the nozzle, now has no opposing force to balance with. It's the force on this unbalanced area that generates the thrust that will propel the balloon when you let go.

There's more to it than this, of course, but this is a good way to visualize how a rocket works. If you do an on-line search for things like "rocket free-body diagram", "Tsiolkovsky rocket equation", etc. you can find a wealth of information about how rockets work. Wikipedia's article about the Tsiolkovsky rocket equation is pretty good and shows derivations based on the momentum balance and based on forces. For an entertaining approach to rocketry in general, check YT for Don Pettit's TED talk, "The Tyranny of the Rocket Equation."

============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

RE: SpaceX foundation slab pulverised

Normal portland cement based concrete will fail due to overheat at realtively low temperatures. To survive higher temperatures ( to 2500 F) , either the concrete needs to be geopolymer concrete, or a thermal radiation shield be provided above the concrete. Thermal stresses can also play a role when rebar reinforced concrete is the subject.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

RE: SpaceX foundation slab pulverised

Would the duration of exposure be long enough to cause significant heating of the reinforcing rebar?

Boiler furnaces operate at similar temperatures. It's most important to heat the furnace slowly to prevent spalling from moisture. Is moisture a problem for the material used in the construction of this foundation?

RE: SpaceX foundation slab pulverised

missiles and capsules that re-enter at thousands of miles per hour keep their cool by ablation, the outer layer spalls off and keeps the inner layer cooler. The same concpet could be applied to the launch pad.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

RE: SpaceX foundation slab pulverised

Boiler burner tiles which see significantly more thermal shock and much higher temperatures than the remainder of a boiler are typically a significantly different refractory material. I would not expect any of the materials used as boiler refractory to withstand the abrasion of hot gas moving at several thousand miles per hour.

The refractory used in electric arc furnace roofs is much more durable, (high alumina (70 % Al2O3 to 90 % Al2O3) precast shapes) but probably would be pressed to survive in the arrangement used here. Electric arc furnace practice now uses water cooled panels in most areas that are not in contact with molten metal. https://www.ispatguru.com/refractory-lining-of-the...

Regardless the first firing of the refractory is a critical process, where the warm up schedule must be strictly followed (more critical for castable than fired brick). The warmup, dry, and soak schedule typically requires many hours, and if the refractory is thick, days.

If the heat penetrated to the saturated water layer, as is exposed in the pictures of standing water in the bottom of the hole, then boiling water will launch and fracture the remaining concrete, it (the concrete) will work about as well as loose sand.

I am in the camp that the refractory needs to be protected from contact with the hot jet with a layer of steam (applied as large quantities of water).

RE: SpaceX foundation slab pulverised

Musk is saying 6-8 weeks until they can try again.

RE: SpaceX foundation slab pulverised

The concrete may not be cured in 6-8 weeks.

RE: SpaceX foundation slab pulverised

Reusable rocket disposable foundation. If the slab can be reconstructed in a few weeks why make it reusable? I ask this question excluding the obvious problem of debris impacting the rocket.

Can the rocket lift off on say, half the engines, and then start the others once clear of the pad for less impact on the ground equipment?

RE: SpaceX foundation slab pulverised

Quote (TugboatEng)

Can the rocket lift off on say, half the engines, and then start the others once clear of the pad for less impact on the ground equipment?

No, that wouldn't work. The rocket is at its heaviest when sat on the pad, due to the fuel. Large rockets have a fairly modest thrust to weight ratio on the pad, needing maximum thrust just to counter gravity and accelerate slowly. Typical rockets have close to the practical minimum of total engine power in their first stage to make it off the pad in a fuel-efficient manner.

With no payload, slightly reduced power on the pad is a possibility.

RE: SpaceX foundation slab pulverised

I don't know how easy it is to get a 'blast diverter' or a water cooling system; I think that's what he requires.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

RE: SpaceX foundation slab pulverised

They are going to have to work something out for a return from the surface of Mars with unprotected launch surfaces.

RE: SpaceX foundation slab pulverised

Or just accept that it is a one way trip.

RE: SpaceX foundation slab pulverised

As its going to be a manned mission I don't think that will be on the cards.

RE: SpaceX foundation slab pulverised

Maybe, maybe not. They probably can find some folks giving up their lives for notoriety.

RE: SpaceX foundation slab pulverised

A return trip from Mars will need 3 or 4 launches of supplies to be possible.
This rocket is far too small for a maned round trip.
Just the basic math for the launch from Mars shows that the fuel required will be significant.
And of course, they will need to make a powered landing (fair gravity, no atmosphere).
They will fix the pad and I am sure that they will go with a diverter/deluge system.

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

RE: SpaceX foundation slab pulverised

Quote:

I don't know how easy it is to get a 'blast diverter' or a water cooling system; I think that's what he requires.

Musk knew that; he simply decided to "go fast and break things." Unfortunately, not only did he break his own things, he broke a bunch of other people's things as well, such as the vehicle that famously gets clobbered in the videos as well as a wildfire in a state park, etc.

https://www.expressnews.com/business/article/coast...
https://www.tpr.org/environment/2023-04-27/photos-...

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: SpaceX foundation slab pulverised

Quote (IRstuff)

"go fast and break things."

Yeah...tech start up mentality works well for tech start ups...less so for aerospace...

RE: SpaceX foundation slab pulverised

Hello,

I've seen several videos regarding NASAs water system and flame trench. One topic that always comes up is mitigation of accoustic damage that can occur to a launch vehicle. The sound waves bounce off the surface back up to the rocket and can cause damage. The water deluge system seems to not only handle the thermal issues but the water flow and steam created also reduce the sound level. I know SpaceX wanted to have a faster schedule but how did they think a rocket with twice the thrust of a Saturn V would not have issues?

The launch pad was not only pulverized, but debris and other factors appear to have taken out a few engines right on the launch pad.

RE: SpaceX foundation slab pulverised

I am trying to understand the dimensional scale of the structure in the photo posted above. Is that a one-story building next to the pylon structure on the right side of the photo and is that a stairway with approximately 3 stories visible inside the pylon structure on the left side of the photo? That's what it looks like to me, and if so, then the scale of that concrete grade beam that got obliterated is quite massive, maybe something like 10 feet thick/deep. Am I seeing that correctly?

RE: SpaceX foundation slab pulverised

I couldn't easily find a reliable looking source for the dimensions. That certainly does look like a permanent access stair on the left. I count 4 semi-enclosed levels, and 2 open levels below the ring structure. I roughly estimate about 3m / 10ft per level, so maybe around 18m / 60ft from ground to the underside of the ring. That's a very rough guesstimate. Possibly as much as about 100ft to the top of the ring; the levels in the stair look quite tall, so maybe more than 10ft.

RE: SpaceX foundation slab pulverised

2
Looks like the base is ~75' tall (ignoring any sort of errors from this perspective). Starship including booster is 394' tall and 29.5' wide.

RE: SpaceX foundation slab pulverised

Some details are coming out. Apparently 3 engines failed to reach full thrust and were shut down on the pad. This loss of thrust ~9% contributed to the rocket's long delay to leave the pad which certainly contributed to the failure of the Fondag (about 8 seconds instead of 2.5 seconds). SpaceX has proposed the possibility that the downward thrust was sufficient to force the Fondag downward by compacting the sandy material below which contributed to the total failure of the blast pad. Supposing both are true, then the absence of either occurrence would certainly have had less consequence.

Brad Waybright

The more you know, the more you know you don't know.

RE: SpaceX foundation slab pulverised

Quote (thebard3)

SpaceX has proposed the possibility that the downward thrust was sufficient to force the Fondag downward by compacting the sandy material below which contributed to the total failure of the blast pad.

That's a pretty interesting take. It would be like an absolutely massive vibratory compactor affecting the soil/sand. Certainly these effects would fall well outside the realm of normal geotechnical engineering scope - i.e., extreme dynamic loading from the largest rocket ever (unless NASA got really into the weeds during the Apollo program, which seems reasonable).

Fortunately it looks like the actual foundation of the launch stand is supported by some gargantuan piles. I'd eyeball those at ~8-10ft diameter? (I had to make another crappy bluebeam markup...)

Here are some cool pics of the construction from this youtube video:









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