We know that to achieve space navigation, the rocket’s speed must theoretically reach at least 7.91 km / s, which is the first cosmic speed. In the 20th century, in order to achieve this speed, countries have adopted multi-stage rockets, which means that the rocket is composed of many “knots”. In this type of rocket, each “knot” of the rocket is a single-stage rocket, which has its own engine, propellant, control system, and servo mechanism. These single-stage rockets are connected in series or in parallel to form a multi-stage rocket. So why do rockets have so many sections?
Let’s make a hypothesis first. If a huge launch vehicle is made into a single stage, the entire propellant can only be stored in the tank of this stage rocket. In this way, not only the volume of the tank must be increased, but also the wall of the tank must be thickened because of the increased propellant load, which will increase the weight of the tank. During the flight of this rocket, the propellant is gradually consumed, and the storage tank is becoming more and more empty. The empty tank shell becomes useless mass, and the energy released by the propellant must not only accelerate the satellite or the spacecraft, but also accelerate this. Partially useless empty storage tank. Moreover, the heavier the tank, the more propellant it takes to accelerate the empty tank, and eventually the rocket cannot reach the speed required for space navigation. In fact, the highest speed that a single-stage rocket can reach is currently no more than 6 km / s, and it is impossible to achieve space navigation. If the useless tank can be thrown away, the final speed of the rocket can obviously be increased, which is why the rocket is made into many “knots”.
When a multi-stage rocket is flying, the lowest first stage works first and makes the rocket reach a certain speed. After completing the mission, this stage is thrown away. Then, based on this speed, the second stage is started to accelerate further. Then use the third or even fourth stage to accelerate. In this way, the “body” of the rocket in flight is thrown away one by one, and the propellant energy will not be excessively expended on the empty and useless acceleration tank. The rocket is lightly loaded. Go forward, fly more and lighter, and speed up step by step. Using this “relay” technology of multi-stage rockets, it is finally possible to surpass the first cosmic speed and achieve space navigation.