Apollo 14 in the context of "Eugene Cernan"

Eugene Andrew Cernan (/ˈsɜːrnən/; March 14, 1934 – January 16, 2017) was an American astronaut, naval aviator, electrical engineer, aeronautical engineer, and fighter pilot.

Cernan traveled into space three times and to the Moon twice: as pilot of Gemini 9A in June 1966, as lunar module pilot of Apollo 10 in May 1969, and as commander of Apollo 17 in December 1972, the final Apollo lunar landing. He was also a backup crew member of Gemini 12, Apollo 7, and Apollo 14. During the Apollo 17 mission, he became the 11th person to walk on the Moon as well as the astronaut with the longest time spent walking on the Moon; he is also the last person to walk on the Moon.

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.

Lunar Laser Ranging (LLR) is the practice of measuring the distance between the surfaces of the Earth and the Moon using laser ranging. The distance can be calculated from the round-trip time of laser light pulses travelling at the speed of light, which are reflected back to Earth by the Moon's surface or by one of several retroreflectors installed on the Moon. Three were placed by the United States' Apollo program (11, 14, and 15), two by the Soviet Lunokhod 1 and 2 missions, and one by India's Chandrayaan-3 mission.

Although it is possible to reflect light or radio waves directly from the Moon's surface (a process known as EME), a much more precise range measurement can be made using retroreflectors, since because of their small size, the temporal spread in the reflected signal is much smaller and because the return will be more evenly reflected with less diffusion.