Eli5.. how did they blast off from the moon to get back to earth?
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You might be asking why they didn’t need a giant rocket like the one that lifted off from Earth.
The main reason is that gravity is so much lower on the moon. You need very little power to escape the moon’s gravity.
Another reason is that they don’t have to carry very much. Most of the weight / size of the main Saturn V rocket was fuel to send everything to the moon.
Someone did the math in 2021 and followed up with orbital computer simulations that suggest it is possible that that Apollo 11 LM is still in orbit and may be detectable. You can Google for it to find the articles and, there is a good YouTube video with info and the orbital simulations that show it just might be up there…
When they took off from the moon why is there no flame present? Even in a vacuum there should be one present. You can see the spacex Draco engine test performed in a vacuum with a flame still present. Also amazing how there is no lag in communication sometimes when they are communicating back and forth. Should take 2.6 seconds minimum and sometimes it’s almost instantaneous.
The real question is how did the Apollo spacecraft even get to the moon if the planets and the moon are speeding through space at hundreds of thousands of miles an hour? The spacecraft reached a maximum speed of only 25,000 mph…
The moon is so much smaller and lighter than Earth that it takes much less powerful rockets to reach orbit around the moon than it does the Earth. If you watch an Apollo mission take off from the moon, you’ll notice a small explosion to decouple the landing module from the landing gear and engine that got it down to the surface, leaving just the pod containing the astronauts and a very tiny engine to carry them into orbit.
From there, they rendezvous with the pilot in the main module and climb back into that vessel with any science they brought. From there, that larger vessel can make the return journey to Earth.
Having a separate landing module was done so they could use at little fuel as possible to perform the actual landing because getting all that weight back up into orbit is the hard part.
They then reached escape velocity for the moon such that they could exit the moon’s influence going in the opposite direction than the moon travels around the Earth (called retrograde) to achieve what’s called a “free return trajectory” this was done with all missions to orbit, land, and flyby the moon because it saves fuel. From there, they just need to slow down enough to not burn up in the atmosphere, and then they can return to Earth.
don’t think many people are aware of how narrow the re-entry corridor back into earth’s atmosphere is. If i remember correctly it’s like between 5 and 7 degrees.
Hit too high and you skip off the atmosphere and float away into certain death, hit too low and you burn up on re-entry.
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They launched with a **much** bigger rocket than needed to escape Earth’s gravity that way they could launch a capsule with enough rocket power to escape the moon’s gravity. If that’s what you’re wondering about.
I think the absolutely simplest ELI5 answer is… they did it [like this](https://www.youtube.com/watch?v=9HQfauGJaTs).
The Saturn V rocket had multiple stages, each with its own engine and fuel load. The benefit of staging is that once you’ve depleted a fuel tank, you can get rid of any extra dead weight and use a different engine which makes it much more efficient.
The amount of energy needed to get into orbit, usually expressed in Δv (meaning the difference in speed you can generate with a given engine and fuel load) is much smaller on the Moon due to the absence of an atmosphere and the much lower gravity. This means that while the rocket that takes off from the Earth needs to be huge and powerful in order to make it into orbit, the rocket that you need to get in orbit around the Moon can be much smaller and less powerful.
The Saturn V had 5 stages. The first two were used to get the rocket to Low Earth Orbit. The third stage was used to do the “Trans-Lunar injection”, which is to set the course for encounter with the Moon. The last two stages were the Command Module (CM) and the Lunar Module (LM). When in space the nacelles protecting the LM would be jettisoned and the LM would be reorientated and docked with the CM. Once over the Moon the CM would use its engine and fuel load to establish a stable orbit around the Moon. Then, two crew members would enter the LM and one would stay on the CM in orbit. When it was time for the crew to leave, the LM would lift off from the Moon’s surface, separating from its landing gear and any extra weight it didn’t need any longer, and meet up with the CM in orbit. Once the crew had transferred inside the CM, they would separate from the LM and return to Earth. With this method they minimised the weight they had to carry around at any point to the possible minimum.
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