Flying out of the earth and landing on other planets is not a great thing, but being able to come back is a "master"! The American moon landing is already a thing of the last century. With the continuous improvement of scientific understanding and technological level, there are more and more doubts. After the spacecraft lands, how to return is a big technical problem, especially in the last century.
You must know that the Apollo was brought to the sky by the Rhea V carrier rocket. The thrust of this rocket is still ranked second in the world, but there are no such powerful rockets and launch towers on the moon.
The key to the problem of return is gravity, because the background of the event is Earth-Moon system . To give an inappropriate example, seems to be climbing from the earth to the moon, while returning from the moon to the earth is a downhill tailwind. The return plan is only applicable to the moon, , Mars, , and Venus are not applicable. Now let’s dispel the doubts that the outside world has about mankind’s first moon landing.
Moon landing
From the earth to the moon is divided into:
- The rocket accelerates, overcomes the gravity of the earth and lifts off into the ring earth orbit
- The rocket accelerates again It quickly leaves the earth's orbit and enters the Earth-moon transfer orbit, flies to the moon 380,000 kilometers away, enters the orbit around the moon, has a certain speed, overcomes the moon's gravity, and orbits the moon.
There were no flaws in the landing process, everything went smoothly, but there were some details in the process, which paved the way for the Apollo's return.
Preparation for return
In the process of flying out of the earth, as the fuel was exhausted, Rhea separated one by one. When they entered the earth-moon orbit, the front part of the rocket, that is, the pointed part is the command module and the service module in the middle, separated from the rocket and made a 180-degree rotation.
Picture: The command module turned over, ready to "kiss" with the lunar module
After adjusting the "head" and "feet", it came back to dock with the lunar module in the middle. Look at the big blowhole on the "feet" of the service module. You can also use your feet to know that the service module carries fuel. Immediately afterwards, the command module and service module took the lunar module and the last thruster of and Rhea to separate and enter the earth-lunar orbit.
When the Apollo landed on the moon, humans took a "big step" down, planted small flags, picked up stones, and prepared to go back. Eagle-eyed children may have noticed, where are the "pointy" command module and service module that were adjusted just now? There were also moon landing plans and sent out a total of 3 astronauts. Why did only two of them disembark?
In fact, there was no one on board, because the other astronaut was not on the moon at all. When orbiting the moon in the combined state, Armstrong and Aldrin hid in the lunar module, then separated from the command module and decelerated to land on the moon. And Michael Collins continued to stay in the command module, circling around the moon. The command module was the return vehicle, and he was waiting for the next mission-to take everyone home.
The rocket's escape velocity
The key factor in Apollo's takeoff is the moon's gravity. On the playground, you can throw a ball 30 meters away. If you are on Mount Everest, you can throw it farther because there is a slope between the mountain and the ground. The earth is not flat, but round. If the ball has enough initial velocity when it leaves the hand, so that the ball has already left the earth and has not yet landed, then the following situation will occur:
The ball orbits the earth. To reach the initial speed of orbiting the earth, it is called the first cosmic speed , 7.9 km/s. If the force is stronger, the earth's gravity cannot change its mind, and the following situation will occur:
This situation is called escape, and the earth's escape velocity is also called the second cosmic speed , 11.2km/s.The escape velocity is only related to the mass and radius of the celestial body, and the mass and radius determine the gravity of the celestial body. Therefore, scientists often use the escape velocity to describe the gravity of the celestial body. For example, black holes, light at the highest speed in the universe cannot escape, so the gravity of a black hole is extremely strong.
Returning from the Moon
The moon has a very small gravity, and its escape velocity is 2.4km/s. Armstrong was wearing a heavy spacesuit and was jumping carefully when he walked. If it jumped hard, it would probably beat the pole vault record on Earth in seconds. This means that there is no need for a propeller as powerful as Rhea on the moon. It only needs to be equipped with a "mini rocket" and a "mini launch pad."
The Apollo lunar module was divided into two parts. The lower part was the descent stage. It carried a small amount of fuel and could steadily land the spacecraft on the lunar surface. When the spacecraft is about to leave, the upper part is unlocked and transformed into a launch pad. The upper part is an upgrade and also carries a small amount of fuel and engines. This mini structure is enough to support it in overcoming gravity and flying away from the lunar surface. When the lunar module was upgraded and returned to lunar orbit, docked with the command module, the return home was passed to the "large-capacity jet" (service module).
In fact, during the entire process, except for people and stones, the entire moon landing was abandoned on the moon. The descent stage serves as a launch pad and remains permanently on the lunar surface. The upper part is that after the command module is docked, the two astronauts of the lunar module enter the command module with the "stone". Then the lunar module in the ascent stage separates from the command module and is abandoned in the orbit of the moon. As it slowly decelerates, it will eventually fall into the lunar surface. So why does a moon landing have to be divided into parts?
Choice of various plans
Several plans for the moon landing were envisaged at that time:
- Take off directly
The rocket will take off with the spacecraft to the moon and land on it. After taking the stones, the rocket will take off again and return to the earth.
- rendezvous in the earth orbit
The rocket can be smaller, but two of them can be used to send the lunar module and the command module to the earth orbit for docking, then fly to the moon, and then return as a whole.
Picture: Imagination of direct takeoff or Earth orbit rendezvous
- Moon surface rendezvous
also uses two ships, one is unmanned and lands on the moon with thrusters, and then the manned lunar module reaches the moon. The astronauts take the stones and enter the spacecraft that arrived earlier, and then push up and return to the earth.
Picture: The whole process of the lunar orbit rendezvous plan
- Lunar orbit rendezvous
This plan is the plan used for the Apollo moon landing. A large rocket carries two spacecrafts. The larger one is loaded with fuel and daily necessities for returning to the earth, as well as the heat shield needed to assemble into the earth's atmosphere. This part does not go to the moon, but only circles the moon. The other one is lightly packed and has a smaller mass. It only carries people and a small amount of fuel required to land on the moon and return to the lunar orbit from the lunar surface. After all the fuel in the service module was used up, only a small cone of the command module remained, entering the atmosphere and falling into the sea.
Energy
The last option was chosen due to energy considerations. The spacecraft requires energy mainly to overcome gravity to take off and change orbit. There is no need to consider energy issues when flying to the moon, because we have a complete launch pad and powerful rockets.
But it will be stretched when it rises to the moon. Although the moon's gravity is small, it still needs to reach a certain initial velocity before it can take off and ascend to the lunar orbit. The greater the mass, the greater the energy required for takeoff acceleration, so the mass of the moon landing part needs to be compressed to the minimum as much as possible.
The emblem of Apollo 11 is an eagle landing on the moon. Viewed from the side, this is a very vivid metaphor. The lunar module is like an eagle. It looks very big, but in fact it is not heavy. The main mass is concentrated under the feathers.The eagle's claws represent the descent section of the lunar module. The two claws can be separated during landing to firmly lock the ground.
The wings represent take-off. After completing the mission, the eagle's claws become a launcher fixed on the ground and remain on the moon. The fuel and thrusters carried in the ascent stage are like the eagle's wings that flap and take them off. Finally, the eagle completed its mission and stayed on the moon. The larger spacecraft (Service) has enough fuel to make several orbit changes, coupled with the gravitational pull of the Earth as the dominant force in the Earth-Moon system, the stone and the astronauts will eventually return home.
Mars will not come back
The whole process of landing on the moon was very smooth and perfect, and there was nothing to question. They have been aiming at Mars for a long time now. The one-way journey to Mars takes at least 39 days, while the round trip to the moon only takes 8 days. The distance indicates the fuel. Mars is much larger than the moon, and its escape velocity is about 5km/s. Sending a probe and landing vehicle to Mars will not be a big problem for humans.
If you want to take off from Mars and return to Earth with a large amount of fuel and living supplies, it will be difficult. Mini launchers and engines cannot make the behemoth reach escape speed. We need to have a launch base on Mars and be able to use and mine the fuel on Mars to return. Therefore, Americans have not sent anyone to Mars so far.
The end of the Apollo program
Since Apollo 11, after Armstrong gave up, the Apollo program has successfully landed on the moon many times and planted many flags everywhere on the moon. In the end, it was tired. It also picked up the stones that should be picked up. There was no novelty. The key is that it was super expensive. So after Apollo 17 , the Americans terminated the Apollo program. Being able to take a big step forward and then take another step back is what a master does!
The escape velocity is only related to the mass and radius of the celestial body, and the mass and radius determine the gravity of the celestial body. Therefore, scientists often use the escape velocity to describe the gravity of the celestial body. For example, black holes, light at the highest speed in the universe cannot escape, so the gravity of a black hole is extremely strong.
Returning from the Moon
The moon has a very small gravity, and its escape velocity is 2.4km/s. Armstrong was wearing a heavy spacesuit and was jumping carefully when he walked. If it jumped hard, it would probably beat the pole vault record on Earth in seconds. This means that there is no need for a propeller as powerful as Rhea on the moon. It only needs to be equipped with a "mini rocket" and a "mini launch pad."
The Apollo lunar module was divided into two parts. The lower part was the descent stage. It carried a small amount of fuel and could steadily land the spacecraft on the lunar surface. When the spacecraft is about to leave, the upper part is unlocked and transformed into a launch pad. The upper part is an upgrade and also carries a small amount of fuel and engines. This mini structure is enough to support it in overcoming gravity and flying away from the lunar surface. When the lunar module was upgraded and returned to lunar orbit, docked with the command module, the return home was passed to the "large-capacity jet" (service module).
In fact, during the entire process, except for people and stones, the entire moon landing was abandoned on the moon. The descent stage serves as a launch pad and remains permanently on the lunar surface. The upper part is that after the command module is docked, the two astronauts of the lunar module enter the command module with the "stone". Then the lunar module in the ascent stage separates from the command module and is abandoned in the orbit of the moon. As it slowly decelerates, it will eventually fall into the lunar surface. So why does a moon landing have to be divided into parts?
Choice of various plans
Several plans for the moon landing were envisaged at that time:
- Take off directly
The rocket will take off with the spacecraft to the moon and land on it. After taking the stones, the rocket will take off again and return to the earth.
- rendezvous in the earth orbit
The rocket can be smaller, but two of them can be used to send the lunar module and the command module to the earth orbit for docking, then fly to the moon, and then return as a whole.
Picture: Imagination of direct takeoff or Earth orbit rendezvous
- Moon surface rendezvous
also uses two ships, one is unmanned and lands on the moon with thrusters, and then the manned lunar module reaches the moon. The astronauts take the stones and enter the spacecraft that arrived earlier, and then push up and return to the earth.
Picture: The whole process of the lunar orbit rendezvous plan
- Lunar orbit rendezvous
This plan is the plan used for the Apollo moon landing. A large rocket carries two spacecrafts. The larger one is loaded with fuel and daily necessities for returning to the earth, as well as the heat shield needed to assemble into the earth's atmosphere. This part does not go to the moon, but only circles the moon. The other one is lightly packed and has a smaller mass. It only carries people and a small amount of fuel required to land on the moon and return to the lunar orbit from the lunar surface. After all the fuel in the service module was used up, only a small cone of the command module remained, entering the atmosphere and falling into the sea.
Energy
The last option was chosen due to energy considerations. The spacecraft requires energy mainly to overcome gravity to take off and change orbit. There is no need to consider energy issues when flying to the moon, because we have a complete launch pad and powerful rockets.
But it will be stretched when it rises to the moon. Although the moon's gravity is small, it still needs to reach a certain initial velocity before it can take off and ascend to the lunar orbit. The greater the mass, the greater the energy required for takeoff acceleration, so the mass of the moon landing part needs to be compressed to the minimum as much as possible.
The emblem of Apollo 11 is an eagle landing on the moon. Viewed from the side, this is a very vivid metaphor. The lunar module is like an eagle. It looks very big, but in fact it is not heavy. The main mass is concentrated under the feathers.The eagle's claws represent the descent section of the lunar module. The two claws can be separated during landing to firmly lock the ground.
The wings represent take-off. After completing the mission, the eagle's claws become a launcher fixed on the ground and remain on the moon. The fuel and thrusters carried in the ascent stage are like the eagle's wings that flap and take them off. Finally, the eagle completed its mission and stayed on the moon. The larger spacecraft (Service) has enough fuel to make several orbit changes, coupled with the gravitational pull of the Earth as the dominant force in the Earth-Moon system, the stone and the astronauts will eventually return home.
Mars will not come back
The whole process of landing on the moon was very smooth and perfect, and there was nothing to question. They have been aiming at Mars for a long time now. The one-way journey to Mars takes at least 39 days, while the round trip to the moon only takes 8 days. The distance indicates the fuel. Mars is much larger than the moon, and its escape velocity is about 5km/s. Sending a probe and landing vehicle to Mars will not be a big problem for humans.
If you want to take off from Mars and return to Earth with a large amount of fuel and living supplies, it will be difficult. Mini launchers and engines cannot make the behemoth reach escape speed. We need to have a launch base on Mars and be able to use and mine the fuel on Mars to return. Therefore, Americans have not sent anyone to Mars so far.
The end of the Apollo program
Since Apollo 11, after Armstrong gave up, the Apollo program has successfully landed on the moon many times and planted many flags everywhere on the moon. In the end, it was tired. It also picked up the stones that should be picked up. There was no novelty. The key is that it was super expensive. So after Apollo 17 , the Americans terminated the Apollo program. Being able to take a big step forward and then take another step back is what a master does!
