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A fuel burning turbine is much more mass efficient than a lithium battery powered one. And hence also makes the whole vehicle more fuel efficient. But a turbin
by Gravityloss 8y ago
A fuel burning turbine is much more mass efficient than a lithium battery powered one. And hence also makes the whole vehicle more fuel efficient.
But a turbine is much harder to develop and manufacture. Especially at small scale, the turbine is also inefficient so it has less advantage to a battery there.
It wouldn't make sense to run the Falcon 9 pumps with batteries.
- Kye 8y agoI wonder how a hybrid approach like they do with freight trains would work. Generate electricity with energy-dense fuel, then use that to drive electric motors.
- Gravityloss 8y agoHard to find any energy denser fuels than the ones they already use for main propulsion. But yes, with a hybrid one, you could decouple the rotation rate of the turbine and the pumps. They have different optimal points. Or you could have more pump stages with different speeds. Some engines use gears for this purpose (NK-33). Some engines use two turbines, one for each pump (SSME). Also startup would be nice and easy.
- Kye 8y ago>> "Hard to find any energy denser fuels than the ones they already use for main propulsion." I phrased that poorly. I meant fuel as a class of things compared to relatively sparse batteries.
- Gravityloss 8y agoAh yes. Still, Soyuz uses different fuel to drive the pumps from the main propellants. Hydrogen peroxide monopropellant for pumps, liquid oxygen and kerosene for main propellants. This is V-2 heritage. Back then the turbine materials were not developed yet that could take the high heat.