Any craft that traveled into space first had to traverse the layers of Earth’s atmosphere, accelerating through the sound barrier and increasing numbers on the Mach speed dial, before escaping the pull of Earth’s gravity and settling into the eighteen-thousand-mile-per-hour speed that locked objects into low Earth orbit, following a circuit of between 134 and 584 miles above the planet. On the return trip, the vehicle skidded through the friction of the increasingly dense atmosphere, building up heat that could reach 3,000 degrees Fahrenheit.
