How does spacecraft propulsion relate to momentum?

Spacecraft propulsion is fundamentally governed by the principle of conservation of momentum. When a spacecraft expels gas out of its engines, it adheres to Newton's third law of motion, which states that for every action, there is an equal and opposite reaction.

When gas is expelled from the spacecraft, it moves in one direction; as a result, the spacecraft experiences a change in momentum in the opposite direction. This process effectively allows the spacecraft to gain momentum in the opposite direction of the expelled gas. Therefore, the momentum gained by the spacecraft as it moves forward is equal in magnitude to the momentum of the gas being expelled backward, in accordance with the conservation of momentum.

This principle is crucial in understanding how rockets operate in the vacuum of space, where traditional means of propulsion are not applicable. The expulsion of gas propels the spacecraft without the need for external air or a surface to push against.

In contrast, the other options either misinterpret the relationship between the expelled gas and its impact on the spacecraft's motion or incorrectly state that momentum principles are not applicable to rocket propulsion. Understanding this fundamental principle allows for insight into how spacecraft can maneuver and travel through space effectively.