 This thing is too big to even fit in my frame and that's amazing. This is my LEGO Saturn V and speaking of the Saturn V a lot of you guys have asked What happened to the upper S4-B stage that launched Apollo to the moon? Well, it was smashed, but smashed for science. All right, here is the Saturn V as much of it as I can fit in this shot. Everything below my right hand here all the way down to the engine bells on this end are the first and second stages. These are the two stages that really did the heavy lifting to get it off the ground. The S4-B stage had a bit of a different purpose. On any Apollo mission to the moon this was the payload that reached Earth orbit. This is the S4-B stage, the third stage of the Saturn V. This is the adapter section that housed the lunar module while it was launched. Here's the service module, the command module, and this is the launch escape tower that was jettisoned quite early in the launch, relatively speaking. So the S4-B stage served two purposes, getting a crew to the moon. The first was that it used its single engine to help get the payload into orbit. So it did fire a little bit during that initial launch, but once it was in orbit this whole stack together minus the launch escape tower, well, should be off from this point, but you get the idea. This whole thing hung out in orbit for a few hours while the crew and Houston did all the systems checks to make sure that everything was ready to go to the moon. So once the crew did get a go for the moon, they had to relight the S4-B's single engine. Now, this would be a burn that would give it enough energy to leave Earth orbit and send it on a trajectory to the moon. Of course, as we know, this whole thing didn't go to the moon and stay in orbit. It was only the service module and the command module that stayed in orbit while the lunar module descended to the surface. So what happened to this? Well, it also went to the moon, only not with a beautifully controlled landing with humans on board. Not long after the translunar injection burn, slash the burn that took them to the moon, it was time for transposition and docking, which is the fancy pants name for turning around and picking up the lunar module. So the crew would separate out the command service module from the adapter section, pull forward, turn around, and then go into dock with the lunar module, which I sadly don't have in this adapter section, but you can imagine what it would look like. Then they would separate the lunar module from the adapter section, leaving the S4-B stage alone. Now, of course, these pedals would fold down and disappear, slash, go off on their own trajectories. So what we would end up with was just this section of the rocket stage. Now, the act of separating the docked command service and lunar modules from the S4-B stage wasn't enough to put any serious distance between the two vehicles. They would not be together, they would not be flying side by side, but they were both on the same trajectory to the moon, which could be kind of dangerous. So NASA figured out a way to make the S4-B stage not smash into the spacecraft with the crew on board. After the S4-B had finished its useful role in the mission, it still had some propellant on board. So controllers on the ground used the auxiliary propulsion system for a burn to put it on a slightly different trajectory than the spacecraft. Now, the exact trajectory depended on the mission. For Apollo's 8, 10, and 11, the S4-B stage was put into lunar orbit. Apollo 12's S4-B was put into Earth orbit. Starting with Apollo 13, however, things got a little bit more interesting. Every lunar landing crew reached the surface with a suite of science instruments in tow, including the ALCEPS, the Apollo Lunar Surface Experiment Package, or in the case of Apollo 11, the ESAP, the Early Apollo Surface Experiment Package. Among the ALCEPS were seismometers and other instruments to measure the force and the effects of meteorite impacts, of moonquakes, and to calibrate these instruments, NASA needed a known data point. Re-enter the S4-B stage. The S4-Bs from Apollo's 13, 14, 15, 16, and 17 were all crashed into the moon. They were crashed at known points at known times to give scientists back on Earth a chance to calibrate their seismometer experiments left by the astronauts. And of course, because every mission left another instrument, the data just got better as there were more and more instruments picking up the crashes of the S4-Bs. And it wasn't just the S4-Bs that were smashed for science. The lunar module-assent stages were also often crashed into the moon for the sake of data points. I've got a video about that right up here. So all the first and second stages of the Saturn V crashed into the Atlantic Ocean, the third stage of that rocket crashed into the oceans on the moon, and also the planes and probably some highlands. If you would like to know more about the experiments that use the crashing S4-Bs as data points, check out my companion blog post over on Discover. I go into more detail, so check that out if you still have questions. But also, let me know what else you want to know about in the comments section below and things for future episodes and all that fun stuff. As always, be sure to follow me on Twitter and Instagram and Facebook for daily content so you never miss updates about what I'm doing next. And of course, for weekly videos right here, be sure to subscribe so you never miss an episode.