Answer to Question #6515 in Mechanics | Relativity for bharath

Question

Is it possible to create a rocket with a variable blast diameter to achieve different levels of torque and power similar to a geared transmission?

I suppose the best analogy I have is the difference in power between a garden hose normally and when you plug it with your thumb, creating more pressure.

Would it be possible to have a rocket launch with maximum diameter, and slowly close up like a camera shutter to gain speed once in the air? Perhaps this shudder would be angled like a funnel to direct the blast easier. All the rockets I see have a fixed diameter and it just makes me curious.

Answer 1

If you kept burning fuel at the same rate, it wouldn't matter. From momentum conservation considerations, all that matters is the rate at which exhaust gases exit the nozzle. And if you kept burning fuel at the same rate, exhaust gases would have to keep exiting at the same rate to avoid an unfortunate pressure build-up in the combustion chamber. If you had a liquid-fuel rocket, you could reduce the rate at which fuel was fed into the combustion chamber so the pressure wouldn't build up. But then, you'd have throttled the rocket down by reducing the rate at which fuel was being used, and you could do that just as well without restricting the nozzle.