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SpaceX Raptor engine – General Thread 4


Amateurs focus on Isp. Experts focus on T/W ratio. ;)

(Obviously you need both, but T/W is really an underrated metric that armchair rocket fans often overlook… Even many aerospace systems engineers, even.)

I understand the T/W is an important metric at the sytem level. I don’t see why it’s important at the engine level, and it fact it’s somewhat arbitrary. I can potentially increase the engine T/W by moving mass off of the engine and onto the non-engine  part of the system. What matters is the mass of the system, not the mass of the engine.
Engine thrust matters. System mass matters, System T/W matters.. Engine T/W doesn’t matter. The designers need to reduce the mass of the system to the extent possible. If it’s easier to remove 400 kg * 33 = 13.2 tonnes of mass from the engines than it is from the chines, or the shields, or the hydraulics, or the grid fins, then by all means do so, but the effect will be the same no matter where that 13.2 tonnes comes from, and this is why engine T/W is meaningless.

I know that wet mass and dry mass are different. I even know that 1 kg of methalox is cheaper than 1 kg of engine. I was attempting to provide a way to look at the relative masses involved.



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