Re: SeaDragon and the Soviet N1



Henry Spencer wrote:


As others have noted, Korolev wasn't able to do proper ground testing
on the N1 first stage, never mind something much larger.


When you think about that, it's odd- because they did build a test stand for the second stage; and one would have thought they could have built one large enough for the first stage that they could then modify to also test the second stage that wouldn't have cost much more than the one they built for the second stage.
It might have been due to the growth of the first stage from its original 24 engine layout to the 30 engine final form, or the fact that there were supposed to be other N-1 derivatives that used just the second and third stages (and one that used just the third stage with a new upper stage on it) as a Proton-equivalent launch system, and maybe the original intention was to build that variant first then add the first stage at a later date.




I thought about the problem of combustion instability. As the engine
size grows this problem grows too, perhaps even faster. I do not
remember it mentioned in relation with Seadragon.



The claim was that pintle injectors are magic and eliminate all such
problems. However, one would be justified in being a bit skeptical about
this claim, given our poor understanding of combustion instability and the
rather radical scale-up involved.


What I wonder about is how you light that engine while it's submerged that deep in the water, which one would think would generate one hell of a back pressure on the engine bell and combustion chamber, due to the need to overcome the water pressure.
I note that the vehicle uses dropable ballast weights to keep it upright for launch, but even with that the PDF shows that the base of the first stage engine bell is going to end up around 300 feet underwater at launch. That's not trivial water pressure.
Also, is the first stage engine bell sealed as it pivots upward in the water? As if it isn't, you're going to end up with a combustion chamber full of seawater which is going to make ignition difficult, to say the least. Or is compressed gas used to expel the seawater once the vehicle is upright?

Pat

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