Question: How much more fuel does a rocket need for every human aboard the rocket?

Hester Baird answered on 15 Mar 2021:

This is a great question, and I’m afraid I can’t give you a definite answer! There is actually a very handy equation that we can use to work out how much fuel a rocket will need. This equation is called the ‘Tsiolkovsky Rocket Equation’, or often just the ‘Rocket Equation’. To work out how much fuel is needed, we need to know how much mass we need to lift into space, so this includes the mass of the rocket (without any fuel) and the mass of any payloads (that could be satellites, spacecraft and humans if it is a crewed mission). We also need to know what the maximum change of velocity/speed of the rocket as it travels into space will be, and how quickly the exhaust gases are expelled from the rocket engines. So, the amount of fuel needed is very dependent on the rocket and engine designs, and where the rocket will be going (we would need a different amount of fuel to take astronauts to the International Space Station than to the Moon).
Because the mass of the rocket and all the equipment on the rocket (which is normally on the scale of tens of tonnes) will be much higher than the mass of any people on board, each extra person won’t make a huge difference to the amount of fuel needed. That being said, it does still need taking into account!