View Single Post
Mech_Engineer is offline
Mar14-12, 10:09 PM
Sci Advisor
PF Gold
Mech_Engineer's Avatar
P: 2,234

High performance rockets

Actually there is a very important fundamental difference between "rockets" and "jets". A jet would be an air-breathing engine which utilizes atmospheric oxygen with carried fuel for combustion, and its maximum speed is limited by its exhaust velocity and of course drag. A rocket carries both the fuel and oxidizer making it a very simply a momentum transfer engine. Therefore a rocket's "theoretical" limit is the speed of light (!!!); practically though it is limited by drag (in the atmosphere) and once in space by the amount of fuel being carried.

Basically for a rocket in space things like the weight of the fuel, spacecraft, etc limit the final speed. I think there might be a trade off rule-of-thumb based on a rocket fuels energy density but I don't know it off the top of my head.