The science behind aerospace propulsion

Outer space is a fascinating place, but also very different from what we are used to on Earth. There is no air, no gravity, no friction, no sound. So how can spacecraft travel, change direction and brake in the vacuum of space? The answer lies in physics, engineering and chemistry.

The action and reaction principle

The motion of spacecraft is based on a fundamental law of physics, known as the "principle of action and reaction". This law states that "if an object exerts a force on another object, the second object exerts an equal and opposite force on the first object". In other words, in every action there will always be a reaction.

An everyday example of this principle applies when we push against a wall with our hands. The wall pushes us back with the same force, but we do not move because we are resting on the ground. However, if we are floating in the air and push the wall, we will move away from it, because there is nothing to stop us.

The same is true for spacecraft. When they are in orbit around the Earth, or traveling through space, there is nothing to slow them down or deflect them except the gravity of the planets and stars. To change their speed or direction, they need to exert a force on something, and that something is the fuel they carry on board.

Spacecraft engines

Spacecraft use different types of engines, the most common being rocket engines, which operate by burning a fuel and an oxidizer, and expelling the resulting gases at high velocity through a nozzle. By doing so, the spacecraft receives a forward force, which causes it to accelerate or change direction.

Rocket engines can be classified into two types: solid fuel engines and liquid fuel engines. The first ones are simpler and more powerful, but cannot be shut down or controlled once ignited. The former are more complex and efficient, but allow to regulate the amount and direction of thrust. Solid fuel engines are mainly used for launching spacecraft from Earth, while liquid fuel engines are used for maneuvering in space.

Another type of engine used by some spacecrafts are ion engines, which work by accelerating electrically charged particles, called ions, through an electric field. These engines produce a very small, but very constant thrust and consume very little fuel. Ion engines are used for long duration missions, such as probes exploring the solar system.

Spacecraft maneuvers

Spacecraft perform different types of maneuvers in space, depending on the objective they want to achieve. Some of the most common maneuvers are:

Ignition: Activation of one or more thrusters to modify the speed or direction of the ship. Used for:

·???????? Earth orbital exit: propel the spacecraft to another planet.

·???????? Orbital entry: Braking the spacecraft to enter the orbit of a planet or satellite.

Course correction: Trajectory adjustments to counteract deviations caused by:

·???????? Gravity of other celestial bodies: Correct path to destination.

·???????? Solar wind: Avoid collisions with asteroids or other space objects.

Gravity assist: Exploiting the gravity of a celestial body to:

·???????? Accelerate or brake the spacecraft without consuming fuel.

·???????? Change orbital plane.

·???????? Reach places inaccessible by other means.

Landing: Controlled descent and contact of the spacecraft on the surface of a planet or satellite. Required:

·???????? Reduction of speed to overcome gravity.

·???????? Protection against overheating due to atmospheric friction.

These are some of the ways spacecraft move in the vacuum of space, using physics, engineering and chemistry. Thanks to these techniques, we can explore the universe and discover its wonders.