What method allows spacecraft to gain speed using the gravity of planets?

The slingshot effect, also known as a gravity assist, is a method where a spacecraft gains speed by using the gravitational pull of a planet. When a spacecraft approaches a planet, it can follow a curved trajectory that allows it to be "slung" around the planet. This interaction with the planet's gravity changes the spacecraft's velocity and direction. As it gets pulled in closer, it accelerates due to the planet's gravity, and as it moves away, it retains this increased speed, effectively using the planet's orbital momentum to increase its own.

This technique is advantageous for interplanetary travel because it allows spacecraft to conserve fuel, enabling them to travel further in space or reach higher velocities without the need for extensive thruster burns. Utilizing the slingshot effect can significantly enhance mission efficiency by effectively borrowing energy from the motion of celestial bodies.