Unlike a commercial airplane, the Shuttle did not have its engines on during reentry. Once it left orbit, it became a colossal glider. The pilots had only one chance to land: if they misjudged the aim or the speed, they couldn't "give it gas" and go around for another try. That's why the engineers affectionately called it "the flying brick" (the flying brick). When it reentered the atmosphere, it traveled at about 28,000 km/h (about 25 times the speed of sound). To slow down without disintegrating, it had to hit the air belly-first, using friction as a brake. In the last kilometers before the runway: • It descended at an angle 7 times steeper than that of a commercial airplane. • While a commercial airplane descends gently, the Shuttle came down "in a dive" to maintain enough kinetic energy and avoid stalling. • It touched down at about 350 km/h, a speed so high that it required a rear parachute to stop before the end of the runway. Under that white-and-black "skin" were thousands of ceramic tiles that protected the astronauts from temperatures exceeding 1,500°C. Without them, the aluminum of the structure would have melted like butter in a matter of seconds.