One of the most important equations you will encounter in rocketry is Konstantin Tsiolkovsky's “Rocket Equation”; given below.

Δv = Ve * ln(Mb / Me)

Equation Explained

• Δv = Final Velocity (Delta-vee) of the rocket in meters per second or feet per second.

• Ve: Velocity of the rocket's exhaust in meters per second or feet per second.

• Mb: Total mass of the rocket fully loaded (with payload, propellant, etc).

• Me: Empty mass of the rocket at burnout with all propellant expended.

The Mass Equation

Mb and Me can be in pounds, kilograms, grams, or tons as long as both use the same unit!

Converting ISP into m/sec or feet per second

Unfortunately, most rocket engine performance levels are given in ISP, not in exhaust velocity. You can however convert ISP into exhaust velocity with the following equation:

Ev = ISP * 9.81 m/sec² (metric)

Ev = ISP * 32.2 feet/sec² (Standard)

Equation Explained

• Ev = Exhaust Velocity of the engine in meters per second or feet per second.

• ISP = Specific Impulse of the engine.