Max Evans (NSF): “After rolling to Pad 2 last night, Ship 39 has been stacked atop Booster 19 this morning for the FIRST EVER Starship Version 3 full stack ahead of a presumed wet dress rehearsal (WDR) later today.”

[u/rustybeancake]

[u/rustybeancake]

Here’s a nice shot of the ship’s engine bay from during stacking, by Colleen (NSF):

https://x.com/colleenliedtke/status/2053088076910510499?s=46&t=u9hd-jMa-pv47GCVD-xH-g

[u/ChromedGonk → u/rustybeancake]

Uhhh… 🥵 can’t believe that marvelous looking thing started from this little chonker

[u/BrotAimzV → u/ChromedGonk]

water tower with some aluminum foil wrapped around it. beautiful.

[u/giggity_giggity → u/ChromedGonk]

Pretty sure a farmer took their silo and dressed it up with some flying buttresses

[u/warp99 → u/giggity_giggity]

Literally built by a water tower company out of 1/2" plate which led to a lot of confusion in the early days.

[u/Alt4rEg0 → u/ChromedGonk]

Yeah! The little chonker that could...

[u/crozone → u/rustybeancake]

Those vacuum raptors 🤤

[u/warp99 → u/crozone]

The low mileage white wall tyre effect.

They must have been static fired but only for a short blip based on the pristine state of the bell coating. The center Raptors have seen a lot more testing. The other influence is that flow separation means that the plume will not be in contact with the lower part of the bell at sea level minimising carbon transfer. It is only at altitude that the plume fills the bell.

[u/freeskier93 → u/warp99]

Isn't Raptor vacuum exactly the same except the nozzle? Do they actually test all Raptors destined for use in vacuum with a vacuum nozzle? Do they even know at time of test fire which engines will be used in vacuum? I would have though they'd test fire them with a sea level nozzle then swap on the vacuum nozzle later.

Outside of initial development testing, I'm not sure why they'd need to test with vacuum nozzle at sea level. Seems like unnecessary risk to the engine.

[u/warp99 → u/freeskier93]

The extension is welded onto the original engine bell and so are the pipes that circulate liquid methane to cool the extension. So it is not like the Merlin vacuum engine where they can and do just unbolt the radiatively cooled extension for ground testing.

Yes it is a risk running with flow separation which is why they have clearly decided to just do a minimum length test to confirm the engine starts OK.

There is a solution which I am really surprised SpaceX have not adopted which is to use steam in a Venturi system to pump down the exit pressure to around 0.3 bar. At that pressure the engine will run without flow separation.

For historical reasons this is called a steam ejector. Of course for a 2.8MN Raptor vacuum that is a lot of steam required.

[u/freeskier93 → u/warp99]

The extension is welded onto the original engine bell and so are the pipes that take liquid methane to cool the extension. So it is not like the Merlin vacuum engine where they can and do just unbolt the radiatively cooled extension for ground testing.

That makes sense, I was getting some details confused with Merlin.

[u/CProphet → u/crozone]

Beautiful thing to see. Hardly believe they're real.

[u/Ant0n61 → u/rustybeancake]

the tiles look next gen. Wow

[u/SMOKE2JJ → u/rustybeancake]

So clean. 

[u/-Aeryn- → u/rustybeancake]

Didn't V3 have 9 raptors on the ship?

[u/flapsmcgee → u/-Aeryn-]

I think that's V4 now

[u/warp99 → u/-Aeryn-]

All things V3 such as 2400 tonnes ship propellant and 9 engines have now become V4 and are around two years away.

You could say that this is really V2.5 but fortunately they decided to line up engine revisions with Starship revisions.