Spacecraft can move in a total vacuum by utilizing the principle of action and reaction, as described by Newton's third law of motion: "For every action, there is an equal and opposite reaction." This principle is the foundation for the functioning of rocket propulsion systems in space.
Spacecraft typically use rocket engines to generate thrust and propel themselves in the vacuum of space. Rocket engines work on the principle of expelling high-speed exhaust gases in one direction, which generates an equal and opposite force that propels the spacecraft in the opposite direction.
Here's a simplified explanation of how rocket engines work:
Propellant Combustion: Rocket engines carry onboard propellants, which are usually a combination of a fuel and an oxidizer. These propellants are ignited and burned in a combustion chamber.
Exhaust Gas Expansion: The combustion process produces extremely high-pressure and high-temperature gases. The gases are directed through a nozzle at the rear of the rocket, where they expand rapidly.
Conservation of Momentum: As the exhaust gases expand and accelerate through the nozzle, they are expelled at high speeds in one direction. According to Newton's third law, for every action (expulsion of gases), there is an equal and opposite reaction, pushing the spacecraft forward.
Thrust and Propulsion: The force generated by the expulsion of the exhaust gases is called thrust. The spacecraft experiences this thrust in the opposite direction, propelling it forward. By controlling the amount and direction of the expelled gases, the spacecraft can maneuver and change its velocity.
Importantly, rocket engines do not require an external medium, such as air, to push against, as they carry their own propellant and can operate in the vacuum of space. However, the lack of atmospheric pressure in space does affect the design and performance of rocket engines compared to engines used in Earth's atmosphere.
It's worth noting that there are other propulsion methods being explored for spacecraft, such as ion propulsion and solar sails, which work on different principles but still allow for movement in a vacuum.