JoSH@RUTGERS.ARPA (06/19/84)
From: JoSH <JoSH@RUTGERS.ARPA> I think the easiest way to understand why a rocket works better in space is the following simple description of how a rocket works. Consider a box one cubic inch in size. It is in a vacuum but contains air at 100 psi. Thus there is a force of 100 lbs on the inside of each face of the box. +------------+ | ^ | | 100# | |<100# 100#>| (actual size) | 100# | | V | +------------+ Since the forces are equal and opposite, there is no net force on the box. Now remove the bottom of the box. The upward force on the top is now unbalanced (as long as you can keep the pressure at 100 psi...), and the box experiences a net upward 100 lbs force: +------------+ | ^ | | 100# | |<100# 100#>| (actual size) | 0# | | V | Now assume the box is in an atmosphere of 15 psi. The internal pressure is the same but now the unbalanced force on the top is only 85 lbs: 15# V +------------+ | ^ | 15# > | 100# | < 15# |<100# 100#>| (actual size) | 0# | | V | Notice that you can't write 15# up at the bottom *because there is no bottom*. You can burn more fuel (or whatever) to raise the chamber pressure to 115 psi, but that's equivalent to the same thing: it's less efficient in an atmosphere. --JoSH -------