I’m really not happy to write these words, but the unfortunate truth should always be said … No human ever landed on the moon and returned to earth … How did i know? Simple physics!
To start the reason why i am actually pondering this question is because my kiddo asked santa for a space rocket to visit planets, in addition to another gift a book about planets.
So basically that got me interested in space, while on a social network i over-read something interesting, the reason why you see so much smoke when a rocket is launched into space is not due to the smoke generated by the rocket fuel but mostly is a water evaporation, what water? water in the big water pool under the rockets …. why is there a water pool ? because otherwise the amount of heat will cause the rocket to explode! I imagined that exiting the moon will require also a lot of thrust and thus we might need another water pool under the rocket on the moon, so should we take with us water for the water pool (no water on the moon)!
Some rocket science first (don’t worry it’s really simple, just try to stay focused on the main idea):
A space rocket weight on surface 250,000 pounds (113 400 kg), that’s a lot, to get the weight or the force that should be neutralized so that an object could float : W = m * ge
ge is Earth’s gravitational acceleration ,because ge depends on the distance from the center of the earth, ge is different when on surface and when in the different levels of the atmosphere, the actual value of ge is 9.8 m/sec^2 = 32.2 ft/sec^2
Once on orbit ( 200 miles from earth surface, 321 km), go is a bit lower than the ge (go / ge = .907 ), thus the shuttle should weigh 226,757 pounds NOT 0 as many might think. So in other words when in orbit shuttles and satellites are not weightless, in fact they has almost the same exact weight they had on surface, and they are not floating in space … they are falling! But because they are so high in space the earth is spinning and thus their fall is not downward because the orbital speed is tangent to the surface of the Earth, instead the fall towards the surface is exactly matched by the curvature of the Earth away from the shuttle, that means you have the impression that it does not move because earth is moving and because earth is curved, so it is constantly falling and this it’s absolute position is always changing in a way to keep it’s place relative position wise (not very important if you fail to understand the concept, but just to understand that even when in orbit the objects are falling towards earth).
So i think it’s safe to say the objective in-order to get out of a planet, is to reach the orbit and still have enough thrust in the rocket to exit the orbit, once you reach the orbit you no longer need any thrust to counter gravity you can consider the shuttle as floating , even if it is actually still falling towards earth but the fall is almost neutralized by the spinning & earth curve, but you’ll still need thrust to go up the orbit and eventually exit earth entirely and reach the moon.
Once the Shuttle reaches the moon, it can rely on the moon’s gravity to pull it down, but when leaving moon the rocket should have enough thrust to escape it and thus be able to travel towards earth, the moon has 1/6 the Earth mass thus :
gm = G * m Moon / (d Moon)^2 = 1.61 m/sec^2 = 5.3 ft/sec^2
Also moon’s orbit (known as Selenocentric orbit) is much lower than earth’s orbit, it is 62 miles (100 km) from the moon’s surface.
That means a shuttle or module needs 1.61/9.8 x 1/3 less thrust to reach the moon orbit than reaching the earth’s, that means it needs 0.055 the thrust, that’s 5.5% of the force needed for same shuttle on earth … but keep in mind that on earth the shuttle was much bigger and heavier and had to use a multistage rocket in order to lose the unnecessary weight while leaving earth …
Apollo 11 : The only human landing on the moon – July 20, 1969
To launch the Apollo 11 spacecraft, a delivery system using Saturn V rocket was used, Saturn V has 3 stages and weigh 6,200,000 pounds (2,800,000 kg), Saturn V can carry a payload of 260 000 pounds (120 000 kg) to the lower earth orbit or a payload of 100,000 pounds (45 000 kg) for trans-lunar injection (sending it to the moon).
Now let’s assume the second way round, the return to earth, we will ignore the trans-Earth injection, we will assume this stage is taken care by a lunar shuttle already in place or that split and is orbiting the moon(Columbia), to send Eagle (lunar module) and Columbia to the moon we needed a 6,200,000 pound delivery system thus we assume we need only 5% of this power to send them back to earth, that’s 310 000 pounds (140 000kg), that’s 140 000kg of pure rocket fuel, but the entire system sent by Saturn V towards the moon weigh 100,000 pounds or 45 000 kg, let’s assume that Eagle doesn’t need such a big thrust, afterall we are leaving columbia in lunar orbit, so no need to count it, assuming Eagle is 1/4th of the lunar payload, it will need 35 000 kg , again something is wrong here, Eagle needs to be the biggest part of the payload because it has the most difficult task which is leaving the moon orbit thus needs to hold fuel, but holding fuel means it will be bigger ….. for a moment let’s assume Eagle had some sort of a miracle fuel or solid fuel that needed no much space, the trans earth injection (done by columbia) needs fuel as well.
Columbia + Eagle (the payload of Saturn V)
So basically the moon shuttle needed Saturn V a 6,200,000 pound delivery system to reach the moon but had only 100,000 pound (45 000 kg) delivery system+ shuttle to return to earth from the moon! 45 000 kg is the weight of a loaded truck! , fitting a command center, navigation system + propulsion enough to escape the moon gravity in a 45 000 kg is almost impossible with current technology, let alone a technology that existed in 1969!
The Russians are still to this day skeptical that the US. landed on the moon!
Why the Mission was never repeated?
Why we hear about one way human missions to Mars and Jupiter moons?