Different stages are needed to send a rocket into space because it takes a lot of energy to reach orbit, and the rocket needs to be able to shed weight as it goes to conserve that energy.
The first stage of a rocket’s launch is typically the most powerful, as it needs to get the rocket off the ground and moving upward against gravity. Once the first stage’s fuel is depleted, it is detached from the rest of the rocket and falls back to Earth. This shedding of weight allows the remaining stages of the rocket to operate more efficiently, using less fuel and achieving greater speeds.
The second stage usually continues to burn for a longer period of time and at a higher altitude, reaching orbital velocities.
The third stage, if necessary, is used to make minor course corrections and fine-tune the rocket’s trajectory.
In addition to shedding weight, multiple stages also allow for the rocket to be optimized for each stage of the journey. The engines used in the first stage are often designed to produce a lot of thrust for a short period of time, while those used in later stages may be designed for longer burns and greater efficiency.
Overall, multiple stages are necessary to optimize the rocket’s performance and conserve energy, allowing it to reach orbit and beyond.