RETURNING HOME IS A TRICKY TASK
Get the trajectory wrong and an incoming spacecraft will simply burn up
As dangerous as the space environment is, the biggest hazard faced by astronauts is returning safely to Earth. The goal here is to get your hefty spacecraft, travelling at immense speeds, to a complete stop at a particular location, through more than 70 miles of dense atmosphere, without it overheating or being shaken apart.
It’s a difficult task, and you only get one chance to get it right. The angle the spacecraft makes on entering the atmosphere is crucial. If it’s too steep, the spacecraft will burn up. If it’s too shallow, it will skim off the atmosphere like a stone off water. All spacecraft re-entries are meticulously calculated, with precise deorbit burns enabling the craft to hit the atmosphere at exactly the right position, angle and speed.
Once they’re hurtling through
Earth’s atmosphere, spacecraft tend to heat up. This is caused not so much by friction as by the compression of atmospheric gases. Temperatures at the leading edges of re-entry vehicles can reach as high as 1,700 degrees Celsius, and so they need to be protected by heat shields. What happens when this barrier is damaged was sadly demonstrated by the Columbia disaster of 2003, in which seven NASA astronauts lost their lives during re-entry.