Introduction to Space Exploration - The X Series

Even before World War II ended the United States began developing rocket-powered planes. In 1943 the NACA initiated the research program in conjunction with the Air Force and Navy. Because the planes were experimental, they were given the name X-aircraft. In 1944 a company called Bell Aircraft began work on the X-1. At first it was called the XS-1, with the "S" standing for supersonic. Later the "S" was dropped from the name.

On October 14, 1947, a young Air Force captain named Charles (Chuck) Yeager flew the X-1 at the speed of sound, which is known as Mach 1. The X-1 was only the first of many high-performance planes tested in the program. Eventually X planes flew at speeds up to six times the speed of sound.

The X-series were high-speed, high-altitude planes unlike any ever built before. Most of them were tested over desolate desert areas near Muroc, California. Daring young test pilots flew the X-series planes. Unfortunately this was a very dangerous profession. Numerous pilots were killed or seriously injured while testing X-series planes. The pilots who survived became the first men considered for the nation's astronaut program.