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Elon Musk recently mentioned a Thrust Puck on Twitter, "We’re stripping SN2 to bare minimum to test the thrust puck to dome weld under pressure, first with water, then at cryo."

He also mentioned this: "There’s a puck at the base that takes the engine thrust load. Don’t shuck the puck!"

What exactly is a Thrust Puck?

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Starship is a 9 meter wide vehicle. The first stage (Super Heavy) will be mounting 35 or 38 or some other number in that range of sea level engines.

As you can imagine that will take at least three separate rings of engines. 6 in the center, then two more rings with the rest.

The Starship is the same diameter as Super Heavy, and the inner ring will be just three sea level engines, and an outer ring of 3 Vacuum optimized Raptors.

The bells on a Vacuum nozzle vs Sea Level is much much bigger, but basically the center of the bottom dome is where the three sea level engines mount. This is actually mounted/welded into place, after the rest of the bottom dome is built.

Thus the thrust puck is that center small disc with all the thrust running through it, on the early Starship builds.

Finally found a source, in this article Musk is interviews and says:

“Well, I just had a lot of talks with the team about that today,” he said of the SN1 failure. “It’s what you might call the thrust puck—there’s an inverted cone where we mount the three sea-level engines. In fact, it’s drawn on that whiteboard over there.”

The Puck looks different on the MK1 build (Starhopper, welds failed on the pad during a pressure test) than the SN1 (lower weld failed on the pad during a pressure test).

Nomenclature: First build flew on one Raptor, one flight, battleship build. (12mm Stainless steel) MK1 - built in Boca Chica (pressure test failure) (4mm stainless going forward) MK2 - built in Florida, sitting idle as of this writing.

SN1 - next build in Boca Chica (pressure test failure) SN2 - next build in Boca Chica

Looking up at the engines on Mk1

The above picture you can see the center where the engines are attached as the Thrust Puck on the MK1 build.

Thrust Puck from Starhopper

In this picture (from the Mk1, or Starhopper, not the SN1 under discussion) you can see the LOX and CH4 manifolds and the TVC attach points in the center. But the entire disc is NOT the full 9m diameter of the bottom dome, it is welded into the center. I propose this is the thrust puck.

During construction of the Mk1 (Starhopper) the thrust puck was captured being lowered in to be welded into the outer ring as shown below.

Dropping the puck

I am trying to find a picture of the dome with the missing center for the puck to be welded into but not having any luck. So the dome to sidewall welds were the initial problem. They think they solved that. Then this time it looks like it failed at that center puck in the middle of the bottom dome.

Here is a bad picture of the thrust structure with the dome sticking out and the space for this puck to be welded available and not yet welded in. This is the SN1 build.

Thrust Structure upside down

Here is a bad screen cap from a video of the structure being turned over and you can see the puck in the center, sort of, and this is from the SN1 build.

Turning the thrust structure

A fan has suggested that the layout of the bottom the vehicle, plumbing to engines, and thrust puck should look something like this image.

Suggested Thrust structure and plumbing layout

The inverted cone was found amongst the wreckage looking like this picture.

Inverted cone thrust puck

The structure on the right is the opening for one Raptor to feed CH4 from the bottom tank and the tube sticking up is the LOX feed connector.

Mar 6th they moved the SN2 lower tank to the launch/test pad for pressure tests. Nomadd got some great photos of the thrust puck.

SN2 Thrust Puck

The SN2 vehicle was truncated to just the lower tank for pressure testing and SN3 started construction instead.

The SN3 vehicle under construction had to be flipped, (They build the bulkhead for the engines upside down, attach the rings around it, then flip it). This gives some EXCELLENT views by Maria of Boca Chica (See watermark in image) of the inside of the thrust puck. (That is, looking down the open top, at the top side of the mount point).

Looking at the inside of the tank

And then they flipped it and we have a great shot of the bottom view now as well.

Outside of the mount point

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    $\begingroup$ @uhoh, agreed, the Y shape in the middle appears to be a propellant manifold and the roughly rectangular objects with circular openings in them appear to be the mount points for the engines, and all the thrust should be applied there. But I am no expert on these vehicles. Had I not read this answer I would have assumed that the entire circular structure shown in the bottom picture was the device in question. Maybe a hand drawn red circle or arrow is in order. $\endgroup$ – Organic Marble Mar 2 at 23:16
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    $\begingroup$ In that case, I shall start making ridiculous stuff up to see if you can catch it, @OrganicMarble I need to find a picture of how they welded the bottom dome, where there is an outer ring, and the imaged item is welded into the center. $\endgroup$ – geoffc Mar 3 at 11:12
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    $\begingroup$ Excellent work! Very clear how the engines mount to the puck and the puck is welded to the tank. Very clear how the thrust forces get distributed through the thrust puck up through the tank walls and the rest of the rocket. Good research! Good work! $\endgroup$ – D_Bester Mar 3 at 13:05
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    $\begingroup$ That picture of it being lowered down on cables is helpful. Is that whole truncated cone the puck? That makes more sense to me. $\endgroup$ – Organic Marble Mar 3 at 14:48
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    $\begingroup$ But the bottom-most picture looks nothing like the others. Again, some hand drawn red arrows and labels would really help. $\endgroup$ – Organic Marble Mar 3 at 15:09
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To those who want more specificity. Pictures are borrowed from post from geoffc.

Elon Musk: There’s a puck at the base that takes the engine thrust load.

In the photo below the three engines are mounted at the green circles. The thrust puck distributes the thrust from the engines to the larger structure. The entire structure circled in red is the "thrust puck".

Thrust Puck

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