North American X-15

There are certain planes that are almost spaceships. It is hardly surprising that this hypersonic aircraft is regarded as the fastest in the world given that its top speed is Mach 6.72, or roughly 4,520 miles per hour. It was first presented in 1959 and is an experimental high-speed rocket-powered aircraft. The North American X-15 made flights above 80 kilometers in altitude, hence they are already considered astronauts. However, given that two of these missions were over 100 kilometers in height, they can be categorized as space trips.

The X-15 evolved over time. For instance, the aircraft used two rocket engines during its initial flights. Later flights switched to a single XLR99 rocket engine powered by liquid nitrogen and ethanol.

The X-15 is a well-known and important figure in aviation history. Its goal was to fly quickly and high, testing the aircraft and putting the pilots through challenges that might later face astronauts. In addition to being the first piloted aircraft in the world to reach hypersonic speeds, or more than five times the speed of sound, it made the first manned flights to the farthest reaches of space. In the 1960s, the X-15 was a crucial tool in the development of spaceflight, and X-15 pilots who flew at altitudes greater than 50 miles were awarded astronaut wings.

Between 1959 and 1968, three X-15s were built and flew 199 times. The program was a collaboration between the US Air Force, Navy, and NASA, and four of its 12 pilots were Air Force officers. In 1967, one pilot, USAF Maj. Michael J. Adams was killed in an X-15 crash. Neil Armstrong, another X-15 pilot, went on to become the first man to walk on the moon.

Technical Notes
Crew: One
Engine: Reaction Motors XLR-99 of 50,000+ lbs. thrust
Ceiling: 354,200 feet (67 miles)
Maximum speed: 4,520 mph (Mach 6.7)