Re-entry into Earth's atmosphere from space is arguably as complex as launching a rocket into space. The Space Shuttle travels with orbital speeds in excess of 30,000 kilometers per hour (18,000 miles per hour) and must come to rest on Earth's surface. How does the pilot accomplish this task without breaks? Atmospheric drag.

The re-entry process begins on the other side of the globe. If the shuttle is landing at Kennedy Space Center in Florida, procedures begin over the Indian Ocean, when de-orbital engines are fired that reduce the shuttle's velocity by about 325 kilometers per hour (200 miles per hour), bringing the shuttle into the upper atmosphere.

Traveling at Mach 25, the shuttle encounters higher density air in the lower thermosphere at an elevation of 120 km (400,000 feet). The vehicle tips its nose up 40° to produce drag which slows the shuttle and reduces heating.

Over time, the 40° angle will cause the angle of descent through the atmosphere to flatten out. To combat this, the shuttle performs four steep, S-shaped curves while maintaining the 40° angle. This occurs during the hottest phase of re-entry and helps the spacecraft to slow down.

The transition from spacecraft to aircraft is complete. The vehicle lowers its nose and approaches head-on toward the landing site as a glider.

The landing phase begins when the shuttle is about 12 kilometers (7.5 miles) away from the runway. At this point, it is 3,000 meters (9,800 feet) up. The pilots apply aerodynamic braking to slow the vehicle from 680 km/h (425 miles/h) to about 346 km/h (215 miles/h) at touchdown. Compare this to the speed of a jet plane when landing, which averages around 270 km/h (170 miles/h).

This entire process, from 18,000 miles per hour to zero speed, takes about an hour and begins halfway around the globe.

The process of slowing the Space Shuttle from orbital speeds in excess of 25,000 kilometers per hour (15,000 miles per hour) to about 350 kilometers per hour (215 miles per hour) at touchdown produces heat that would normally destroy the spacecraft without the use of thermal protection systems. During re-entry, the shuttle must pass through Earth's atmosphere which increases the heat load on the vehicle to approximately 1,600°Celsius (3000° Fahrenheit).

As the shuttle travels at supersonic speeds through the upper atmosphere, the air passing over its forward-facing surfaces produces the immense heat. Thanks to the heat shield and other thermal protection, the heat is largely absorbed and radiated and does not heat the entire vehicle.