How Astronauts Survive
Reentry is during the end of the mission when the spacecraft returns to Earth's atmosphere. This is one of the most dangerous stages of the mission because of the high velocity in the Earth's atmosphere. The friction from the atmosphere acts like a brake on the spacecraft, drastically slowing its speed. But this friction also heats the outer layer of the spacecraft to extremely high temperatures. Temperatures were recorded to be over 2,750° F, which is hot enough to melt gold or silver!
Earlier spacecrafts had heat shields in the front in order to protect the spacecraft and the astronauts from burning up. Instead, the heat shield itself would gradually melt and vaporize, carrying the heat away.
The space shuttle on the other hand, utilizes highly heat-resistant, silica-covered ceramic tiles that did not burn away. In fact, the tiles are capable of withstanding the intense speed. The high temperature around the shuttle also creates a barrier of heated molecules that no radio signal can penetrate. During reentry, all communications with the astronauts and Mission Control are cut off.
One other very important factor is the angle of reentry. The spacecraft must enter the Earth's atmosphere at just the right angle or else the following might happen:
If the angle of reentry is too steep, both the heat and the pressure forces will damage or simply incinerate the spacecraft.
If the angle of reentry is too shallow, the spacecraft might bounce off the atmosphere and back into space, similar to a rock skipping off water.