Eli5.. how did they blast off from the moon to get back to earth?
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The moon has a lot less gravity than the Earth, so a “tiny” push is needed to get off the surface and then you can almost fall to Earth from there.
The moon’s gravity is very weak in comparison to Earth’s, theree is virtually no atmosphere to slow a vehicle down, and the ascent module was very small/light, since it didn’t have to contain the descent engine/fuel/supplies and only needed a very short duration of life support supplies for the two crew. (Only about 35,000 lbs total, while the whole Saturn v launch vehicle weighed over 6,000,000 lbs)
In short, a smaller rocket. The Apollo missions followed a structure that’s now named after them, Apollo-style landings. That’s where you have one stage (the cylindrical shiny chrome part with the really big engine bell, called the Command Module or CM), and a small lander carried by it (called the Lunar Module or LM).
The rocket, the Saturn V, exists to fling both of these modules, together, towards the Moon. Once there, its the CM’s engine that does the manuevre to slow down into Lunar orbit. The LM then detaches, and goes down to the surface with two astronauts while the third stays in orbit with the CM.
The LM consists of two stages, two parts attached together. The first stage, or descent stage is the lower portion, everything that’s covered in gold foil. It contains fuel, engines, and the landing legs. That’s the bit that lets them land. Once they’re ready to depart, they detach the second stage, the ascent stage, from the descent stage and fly it up on its own, as it also has fuel and engines. It functions like its own mini rocket, but it doesn’t need to be pointy or aerodynamic because there’s no air on the Moon to worry about. There are two stages because the landing legs, landing engine and the empty fuel tanks from landing are no longer needed and would simply be dead weight, meaning they can just be thrown away. In this case, they just stay on the surface.
The ascent module takes the two astronauts all the way up back into Lunar orbit, where they meet up with the third astronaut who stayed on the CM. They dock, everyone gets into the CM, they detach the lander and its the CM that takes them back to Earth. The cone shaped tip of the CM is the capsule where the astronauts stay, and it too can detach. Once ready to enter the Earth’s atmosphere, it detaches and only the capsule makes it to the ground as its the only bit that has a heatshield to protect it from the hell of atmospheric entry. It deploys parachutes once slow enough, and if everything has gone right the astronauts splash down in the Pacific ocean safe and sound.
The Apollo Lunar Module had an ascent stage which used the ascent propulsion system (APS) or lunar module ascent engine (LMAE). It was a hypergolic rocket engine, which means that it used two substances which would spontaneously ignite when mixed. The engine weighed 180 pounds and could produce 3,500 pounds of force for up to 2000 meters per second of velocity.
They used a rocket engine. The Lunar Module blasted off from the moon, rendezvoused with the CSM which was still in orbit around the moon, then they jettisoned the LM and used the rocket engine on the CSM to exit the moon’s orbit and return to earth.
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The same way they did on earth: using a rocket engine attached to the lander and some fuel to power it up.
The moon being much, much smaller than the earth, and there being no atmosphere that causes aerodynamic drag, means that you need a fraction of the energy required to take off from earth. In essence, no need for an entire Saturn V to leave the moon and come back to Earth.
The Lunar Module had an ascent engine. It was actually used off-label to help get Apollo 13 back to Earth.
much more easily than the other way around. It takes roughly 5X less energy to get off the moon than it does the Earth.
They blasted back off from the moon. With rockets.
See, they made rockets on earth to get to the moon, but realized that they would wanna come back to earth.
So they made the first rockets big enough to carry extra rockets. That way, when they went to the moon, they already had rockets to blast back off to earth.
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