 It took five massive F1 engines to get to the moon, right? Not exactly. It actually took 83. Okay, admittedly, that's a bit misleading right off the bat. It took 83 rocket engines and rocket motors to get Apollo to the moon. The difference is in the kind of fuel. A rocket engine burns liquid fuel. These engines can be relit in space and also are throttleable. A rocket motor burns solid fuel. They can't be relit and they can't be throttled. Once that thing is burning, it's burning until it's out of fuel. So there were 83 combined rocket engines and motors, basically sources of propulsion needed to get a single Apollo mission to the moon and back to Earth. So let's start the beginning with the first stage. This was the stage that burns the iconic F1 engines. The center engine was the first to ignite and then the external ones in opposite pairs. They all ignited while the rocket was being held down by arms. This allowed the rocket to generate all the thrust and then once it was at full thrust, the arms would pop up and the rocket would be clear to leave the ground. The burn time for engines and stages varied from mission to mission, but on average, the first stage burned for about two and a half minutes. At that point, the first stage separated and fell away from the rest of the rocket. Now, the first stage didn't just separate and fall away. It actually had eight retro rocket motors on the stage to help it gain distance from the upper portion of the rocket. So it would continue rising with the rocket because there was so much energy and velocity behind it. But those eight retro rocket motors would help it slow just a little bit so that this would gain some distance before it had to fire. The first stage eventually fell away and splashed down in the Atlantic Ocean. Meanwhile, it was the second stage's turn to burn. But before that, eight ullage motors on the interstage, which is this little ring right here, had to fire. Now, this is because as the rocket is flying, it's liquid fuel. So the rocket would need to push ever so slightly forward to shove the fuel back so that it could go cleanly into the feed lines. So eight ullage motors on the interstage right here would fire to just kick the rocket a little bit to get the fuel sloshing in the right direction before the main J2 engines on the second stage ignite. There are, like the first stage, five of these engines. Once the spacecraft is high enough that it wouldn't need the launch escape system for a clean abort in the event of an emergency, the launch escape system was jettisoned. That tower jet came courtesy of a single rocket motor and it took the boost protective cover with it at the same time. Like the first stage, the second stage burned for a number of minutes to help propel the spacecraft, which is this part up here, into orbit. And once it was done, once its fuel was expended, it fell away, separating cleanly from the upper stage. Again, the separation wasn't that simple. This tapered section right here is the interstage and it has four retro rocket motors on it to assure a clean separation between the two stages. The second stage is also left to fall in the Atlantic Ocean, and it was now time for the third stage's main J2 engine, its single engine, to ignite. But again, it wasn't that simple. The S4B had two allege motors and two auxiliary propulsion system units on the outside. This was again to help get the fuel pressed up against the fuel lines before the main engine would burn and also for some attitude control. The S4B was the stage whose single J2 engine was relit once the crew was safely in Earth orbit and ready to go to the moon. This gave them the added velocity to escape the Earth's gravity and began a transfer towards the moon. Now on their way to the moon, the crew separated the command service module from the shroud housing the lunar module. They separated, gained some distance, turned around to pick up the lunar module, then separated. At this point, the S4B stage was useless. The crew was clear of it and didn't need it anymore. So NASA engineers sent it on a collision course to the moon where it was crashed for science. I've got a video about that right up here. So now we're down to the bare bone spacecraft, the combined command service and lunar modules. The command service module did most of the work on the way to the moon. It had the main SPS or service propulsion system engine as the big one to do all the bigger course correction burns. But it also had four banks of four thrust rockets. Once the crew was in lunar orbit, the two spacecraft separated. Once separated, the lunar module had to rely on its own propulsion systems. The main one, of course, being the descent engine, the big engine on the descent stage of the lunar module. This was the engine the astronauts used to actually change their orbit to lower towards a lunar landing. But it wasn't enough. They also used thrusters for fine control. And like the service module, the lunar module had four banks of four reaction control thrusters. So this was landing on the moon. But getting off the moon, it needed another engine. It couldn't use the descent stage engine. Notice the crew relied on the ascent module's main engine. All of these engines had to be throttled and in many cases lit multiple times in the case of the SPS engine and the thrusters. They were all liquid engines that used hypergalls. It was the ascent module and the thrusters that allowed the crew to leave the moon and join back up with the command module in orbit. The SPS engine started the flight back to the moon and the SPS engine and the thrusters made all the course corrections needed for a perfect re-entry to the Earth's atmosphere. Of course, no one was going to leave the final mission phase up to chance and just hope that the spacecraft maintained its attitude re-entering through the Earth's atmosphere. And so there were 12 thrust rockets in the command module as well. These helped maintain the spacecraft's attitude as it fell through the atmosphere before the parachutes deployed to effect a soft, comfortable, smooth landing on the ocean surface. I really hope this makes you guys appreciate the awesomeness of the Saturn V just a little bit more. If you have more questions, leave them in the comments below so I can do a follow-up video in the future and, of course, any other questions about old-timey space things you've got, leave those in the comments as well. 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