ABSTRACT
Launch and Reentry Spaceflight became possible with the development of rockets that had sufficient power to break free of Earth’s gravity. To break free, a rocket must reach escape velocity, which is just over 25,000 miles per hour (40,200 kilometers per hour). Takeoff and reentry are the two most dangerous times in a spaceflight. Before the 1950s, some scientists argued that the human body could not survive the stresses of a space launch. The earliest flights by astronauts proved such views wrong. Astronauts have flown faster than any humans have before and have returned back to Earth unharmed.
