Physics: Conservation of Momentum in Spaceflight

Conservation of momentum is one of the most powerful ideas in physics: in an isolated system, the total momentum before an event equals the total momentum after it. Because momentum is a vector, this principle governs not just collisions but any interaction where objects push against one another — including a rocket, or an astronaut, expelling gas to move. This matters enormously in human spaceflight. When a thruster pistol fires, the astronaut and expelled gas form an isolated system whose total momentum stays constant. The gas gains momentum backwards, so the astronaut must gain equal momentum in the opposite direction, propelling her towards the station. The same physics underpins satellite technology, enabling global communications, GPS navigation, and weather forecasting that billions rely on daily.