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A gravitational slingshot, also called a gravity assist, uses the gravity of other objects in space, such as planets, to change the momentum of an object, such as a spacecraft. To understand how this happens, it is crucial to know about gravity. Gravity is the pulling force that keeps us to Earth. But Earth isn't the only thing with gravity. Other planets have gravity, too. This means that if a spacecraft flies near another planet it will be pulled towards the planet. This can be very useful if you want to slow down or speed up the spacecraft. To make a gravitational slingshot increase your spacecraft's momentum, you would need to fly it near a planet. The closer the spacecraft gets, the more the planet's gravity will pull on it, increasing its momentum. When your spacecraft begins flying away from the planet, it will have more momentum than before!