How did NASA's Apollo spaceships propell itself in space?

May 20, 392 by Empathist | Posted in Astronomy & Space

When Apollo's astronauts needed to direct their ship in another direction (to make a course adjustment), how did they do it? What propelled them? It couldn't have been flame, since it was in space. Where as the propulsion (In the front, back, sides of the ship)?
Lastly, how did the pilots see where they were going?

They mostly used the reaction control system (RCS) and service propulsion system (SPS), a system of rocket engines using MMH and N2O4 as propellants. N2O4 or Dinitrogentetroxide replaces the oxygen in the air for the reaction. The combination of these two chemicals has a few advantages - it is liquid at room temperature, meaning they allow using simpler tanks with less insulation, and they ignite on contact with each others, removing the need for complex ignition systems (like spark igniters).

Rocket engines can't use air even when lifting off from Earth. For creating thrust, the pressure at the exit of the rocket engine has to be much higher as the ambient air pressure. The exhaust gases push the air away. That's why all rocket engines require the oxygen to be stored inside tanks and fed into the rocket engines at high pressures.

The navigation of Apollo is a bit more complex. They used an inertial navigation system, called IMU during maneuvers, but because such a IMU uses a lot of electrical energy, shut it off most of the time. For orienting themselves again, they used the stars, Earth and Moon.

Together with calculations from the ground, this was enough to initialize the IMU again and use it.

For rendezvous and landing on the moon, they used also Radar.