When a spacecraft descends back to Earth, the atmosphere in front of it is at a higher pressure than the atmosphere behind the spacecraft. As a result, the air pushes against the spacecraft’s bottom and slows it down. This is called aerodynamic drag.

At around 35 miles (56 kilometers) above the surface of Earth, the air becomes denser. As a result, the drag increases and the spacecraft slows down even more.

As the spacecraft descends, it also experiences friction from the air. This摩擦generates heat. As a result, the spacecraft becomes very hot.

When the spacecraft enters the lower atmosphere, the air becomes denser still and so does the heat. The spacecraft can reach a temperature of 3,000 degrees Fahrenheit (1,650 degrees Celsius). This is hot enough to melt metal.

The intense heat on the surface of the spacecraft protects the astronauts inside. The astronauts are seated in a capsule that is lined with a special heat-resistant material.

When the spacecraft reaches an altitude of about 12 miles (19 kilometers), it deploys its parachutes. The parachutes slow down the spacecraft even further.

The spacecraft continues to descend until it reaches the surface of the ocean. The impact with the water creates a splashdown.

Splashing down is a risky maneuver, but it is the safest way to get spacecraft safely back to Earth.