How does propulsion work? To calculate the specific impulse, we
first need to calculate the exhaust velocity. Since the real
exhaust velocity is exceeding complex to calculate, we will be
using some simplifying assumptions to make a simpler equation.
Assume that the exhaust velocity follows the following formula:
Ve2 = kRgasTc [1 - (pe/pc)(k-1)/k] / (k-1) k = ratio of specific
heats, cp/cv pe = nozzle exit pressure pc = combustion chamber
pressure Tc = combustion chamber temperature Rgas = exhaust flow
specific gas constant RR/MM RR = universal gas constant MM =
exhaust gas molecular weight Note that k is typically between
1.21-1.26 for a wide range of fuels and oxidizers. Also note
that the subscripts (e, c) stand for exit and chamber.
Therefore, pc stands for temperature of chamber and pe stands
for pressure of exit. Because we are just approximating, we can
simplify the above equation. The second half of the equation: [1
- (pe/pc)(k-1)/k] / (k-1) typically ends up as a small number
which we will approximat