North American X-15 in the context of "North American Aviation"

A geocentric orbit, Earth-centered orbit, or Earth orbit involves any object orbiting Earth, such as the Moon or artificial satellites. In 1997, NASA estimated there were approximately 2,465 artificial satellite payloads orbiting Earth and 6,216 pieces of space debris as tracked by the Goddard Space Flight Center. More than 16,291 objects previously launched have undergone orbital decay and entered Earth's atmosphere.

A spacecraft enters orbit when its centripetal acceleration due to gravity is less than or equal to the centrifugal acceleration due to the horizontal component of its velocity. For a low Earth orbit, this velocity is about 7.8 km/s (28,100 km/h; 17,400 mph); by contrast, the fastest crewed airplane speed ever achieved (excluding speeds achieved by deorbiting spacecraft) was 2.2 km/s (7,900 km/h; 4,900 mph) in 1967 by the North American X-15. The energy required to reach Earth orbital velocity at an altitude of 600 km (370 mi) is about 36 MJ/kg, which is six times the energy needed merely to climb to the corresponding altitude.

A sub-orbital spaceflight is a spaceflight in which the spacecraft reaches outer space, but its trajectory intersects the surface of the gravitating body from which it was launched. Hence, it will not complete one orbital revolution, will not become an artificial satellite nor will it reach escape velocity.

For example, the path of an object launched from Earth that reaches the Kármán line (about 83 km [52 mi] – 100 km [62 mi] above sea level), and then falls back to Earth, is considered a sub-orbital spaceflight. Some sub-orbital flights have been undertaken to test spacecraft and launch vehicles later intended for orbital spaceflight. Other vehicles are specifically designed only for sub-orbital flight; examples include crewed vehicles, such as the X-15 and SpaceShipTwo, and uncrewed ones, such as ICBMs and sounding rockets.

A test pilot is an aircraft pilot with additional training to fly and evaluate experimental, newly produced and modified aircraft with specific maneuvers, known as flight test techniques.

Neil Alden Armstrong (August 5, 1930 – August 25, 2012) was an American astronaut and aeronautical engineer who, as the commander of the 1969 Apollo 11 mission, became the first person to walk on the Moon. He was also a naval aviator, test pilot and university professor.

Armstrong was born and raised near Wapakoneta, Ohio. He entered Purdue University, studying aeronautical engineering, with the United States Navy paying his tuition under the Holloway Plan. He became a midshipman in 1949 and a naval aviator the following year. He saw action in the Korean War, flying the Grumman F9F Panther from the aircraft carrier USS Essex. After the war, he completed his bachelor's degree at Purdue and became a test pilot at the National Advisory Committee for Aeronautics (NACA) High-Speed Flight Station at Edwards Air Force Base in California. He was the project pilot on Century Series fighters and flew the North American X-15 seven times. He was also a participant in the U.S. Air Force's Man in Space Soonest and X-20 Dyna-Soar human spaceflight programs.

James Alton McDivitt Jr. (June 10, 1929 – October 13, 2022) was an American test pilot, United States Air Force (USAF) pilot, aeronautical engineer, and NASA astronaut in the Gemini and Apollo programs. He joined the USAF in 1951 and flew 145 combat missions in the Korean War. In 1959, after graduating first in his class with a Bachelor of Science degree in Aeronautical Engineering from the University of Michigan through the U.S. Air Force Institute of Technology (AFIT) program, he qualified as a test pilot at the Air Force Experimental Flight Test Pilot School (Class 59C) and Aerospace Research Pilot School (Class I), and joined the Manned Spacecraft Operations Branch. By September 1962, McDivitt had logged over 2,500 flight hours, of which more than 2,000 hours were in jet aircraft. This included flying as a chase pilot for Robert M. White's North American X-15 flight on July 17, 1962, in which White reached an altitude of 59.5 miles (95.8 km) and became the first X-15 pilot to be awarded Astronaut Wings.

In 1962, McDivitt was selected as an astronaut by NASA as part of Astronaut Group 2. He commanded the Gemini 4 mission, during which Ed White performed the first U.S. spacewalk, and later the Apollo 9 flight, which was the first crewed flight test of the Apollo Lunar Module and the complete set of Apollo flight hardware. He later became the manager of lunar landing operations and was the Apollo spacecraft program manager from 1969 to 1972. In June 1972 he left NASA and retired from the USAF with the rank of brigadier general.

Joe Henry Engle (August 26, 1932 – July 10, 2024) was an American pilot, aeronautical engineer, and NASA astronaut. He was the commander of two Space Shuttle missions including STS-2 in 1981, the program's second orbital flight. He also flew two flights in the Shuttle program's 1977 Approach and Landing Tests. Engle was one of twelve pilots who flew the North American X-15, an experimental spaceplane jointly operated by the Air Force and NASA.

As an X-15 pilot, Engle made three flights above 50 miles (80 km), thus qualifying for astronaut wings under the American convention for the boundary of space. In 1966, he was selected for NASA's 5th Astronaut Group, joining the Apollo program. He was backup Lunar Module Pilot (LMP) for Apollo 14 and was originally scheduled to walk on the Moon as LMP for Apollo 17. However, cancellation of later flights prompted NASA to select geologist-astronaut Harrison Schmitt as the Lunar Module Pilot, displacing Engle.