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.

 

[phamENG]

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

 

[bones206]

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.

 

[zeusfaber]

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.

 

[drwebb]

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

 

[fel3]

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."

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

 

[davefitz]

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

 

[TugboatEng]

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?

 

[EngrPaper]

You can see in another picture in this article that the GSE tanks were hit with debris as well. Gonna take a while to repair/replace.

https://news.yahoo.com/giant-spacex...Gd3avVQzhnRu0GpgNl7WW5LBEKerLnDyuwnpjkPPovMbm

 

[davefitz]

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

 

[FacEngrPE]

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-electric-arc-furnace/

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).

 

[Alistair_Heaton]

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

 

[Cool_Controls]

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

 

[TugboatEng]

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?

 

[Murph 9000]

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.

 

[dik]

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

 

[Alistair_Heaton]

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

 

[hokie66]

Or just accept that it is a one way trip.

 

[Alistair_Heaton]

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

 

[hokie66]

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

 

[EdStainless]

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.

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P.E. Metallurgy, consulting work welcomed