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Comment by neogodless | Hacker News Reader

Presumably not off exhaust?

In automobiles, if they are powered by something other than exhaust (e.g. electricity) are called "superchargers."

Ah quick web search, I believe they do run off exhaust using "pre-burners" that burn before the burn.

They make their own exhaust in a little combustion chamber and use it to blast fuel into the primary at ridiculous volumes. SpaceX is unique in that none of the pre burn is wasted. It all ends up back in the bell instead of leaving out the side. The soviets invented it but it never made it to production. I think it flew once and exploded.

I’m not sure I would say the exhaust is wasted just because it doesn’t go into the main combustion chamber. The exhaust of the turbo fuel pump on one Saturn V F-1 engine provides more thrust than an F-16 in afterburner.

The Raptor is the first operational Full Flow Staged Combustion rocket engine. https://en.m.wikipedia.org/wiki/Staged_combustion_cycle#Full...

Combustion cycles that run the turbopump exhaust into the main combustion chamber are called "staged combustion." The Soviets had staged combustion engines putting payloads in orbit in 1960, and the US flew its first in 1981.

SpaceX's advance was going from oxygen rich (where all of the oxidizer and a fraction of the fuel run through the preburner and turbine, as used in the Soviet/Russian engines) or fuel rich (vice versa, used in the Space Shuttle) to full flow (which has both oxygen- and fuel-rich preburners and all of the propellants flow through one turbine or the other).

The rocket folks call them "turbopumps" rather than "turbochargers," and most of them are powered by a separate combustion apparatus (with non-obvious terminology: if, after going through the turbine, the gas will then end up in the main combustion chamber then it's called a preburner, but if the gas will be discharged outside the main combustion chamber then it's called a gas generator).

There is one type that comes closer to a turbocharger's operation: the "tap-off cycle" runs the turbine on gas drawn from the main combustion chamber rather than using a separate combustor. Tap-off cycle engines aren't common but Blue Origin and Firefly are using them.

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