Comment by c-smile | Hacker News Reader

Comment by c-smile | Hacker News Reader

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N1 (USSR Lunar mission) rocket had similar engine group design - 30 similar engines (NK-15).

I remember one professor in our university who did post-mortem analysis of the program failure.

He compared that setup with 3-body problem (https://en.wikipedia.org/wiki/Three-body_problem) where system exhibits nearly chaotic behavior on small disturbances - not stable. 30+ driving engines just multiply the severity - extremely not stable. Plus parasitic resonances in engines and all such wonders.

N1 had very fat backlink (for that time) to base where control system / computers of the engine pack was located. Sure, computers are better now than when but I suspect problem of controlling such pack is not really solvable due to instability of physical system.

I really want to be mistaken but here is my educated guess - this thing will not fly.

All successful designs so far have one or two main engines, may have additional engines but of significantly lower thirst.

Falcon Heavy flies regularly with 27 engines.

I wonder what analysis was done by the professor.

The N1 failures were attributed to the engines, NK-15, which had too aggressive parameters for the time. The next generation of engines, NK-33, showed much greater reliability.

With the system of such complexity, which was planned to get to work with test launches - because ground-based test systems didn't exist (for the first stage) - it's no big wonder first four launches weren't successful. Even with them the 4th almost completed the 1st stage burn. The chances for the next flight, with NK-33, to be successful at least for the first stage were rather good, and in few more flights they could get to operational reliability.

Time and money were against the engineers, however.

This all doesn't prove ~30 engine stages can't fly. They are more complex - sure, but still.

> All successful designs so far have one or two main engines

What a ridiculous falsehood. Every manned rocket to reach orbit since 1966 has used 5 or more engines. Of those that are currently operational, none have fewer than 8.

Too late to edit so I'll add here. Soyuz first stage is 5 engines, and 5 is less than 8.

Each engine has 4 main combustion chambers and four nozzles so it looks like 20

https://www.flickr.com/photos/nasahqphoto/19853973575/in/pho...

And 2 to 4 steering engines, 3 tons of thrust each, counting them we get to 32.

N1 designers did not have good computers. Chaotic behavior does not mean that system is impossible to control (e.g. double pendulum https://www.youtube.com/watch?v=B6vr1x6KDaY).

It literally has already flown.

> All successful designs so far have one or two main engines, may have additional engines but of significantly lower thirst.

What? The SLS has 4, and its the highest tonnage rated operational rocket in existence. The Falcon Heavy has 27 engines and flies commercial NASA missions

> All successful designs so far have one or two main engines

Falcon 9 has 9 engines and launches weekly...

elon musk is not an engineer...

yea he is, a pretty amazing one

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