Why are chemical rockets so useful when it comes to leaving the planet?

In order to reach a stable orbit it’s necessary to generate enough thrust to overcome the resistances, mainly gravitational and aerodynamic. We therefore consume energy, but what is important is how we consume that energy.

A thrust that is equal to the gravity force would not move the rocket at all. It requires an infinite quantity of energy just to maintain the condition of equilibrium.

Propellant is the main component when it comes to weight before take off. As the rocket becomes heavier, it will require more and more propellant. Technological limits indicate an optimal condition that allows to leave the planet, and the gravitational field, quickly consuming a reasonable quantity of propellant.

Usually to optimize the fuel consumption, rockets are divided into stages. This allows to get rid of components, and weight, that aren’t useful anymore.

I_{sp}=\frac{I_{tot}}{m_{f}g_{0}}
I_{tot}=\int_{0}^{t}Tdx

Chemical rockets have smaller specific impulse compared to electrical propulsion, which is usually choose for orbital maneuvers. That because in space we can build up necessary accelerations in weeks, months or perhaps years. In fact missions last for very long periods and slow accelerations build through electrical systems bring the advantages of having lighter space systems that can cover major distances.

Rockets are used because of the high power they can generate. This way it’s possible to leave the planet in the shortest time at maximum efficiency. Though they have a very short lifetime compared to the electric propulsion systems.

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