Gemini 4 in the context of "Crewed spaceflight"

The Lyndon B. Johnson Space Center (JSC) is NASA's center for human spaceflight in Houston, Texas (originally named the Manned Spacecraft Center), where human spaceflight training, research, and flight control are conducted. It was renamed in honor of the late U.S. president and Texas native, Lyndon B. Johnson, by an act of the United States Senate on February 19, 1973.

JSC consists of a complex of 100 buildings constructed on 1,620 acres (660 ha) in Clear Lake. The center is home to NASA's astronaut corps, and is responsible for training astronauts from both the U.S. and its international partners. It also houses the Christopher C. Kraft Jr. Mission Control Center, which has provided the flight control function for every NASA human spaceflight since Gemini 4 (including Apollo, Skylab, Apollo–Soyuz, and Space Shuttle). It is popularly known by its radio call signs "Mission Control" and "Houston".

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.

Christopher Columbus Kraft Jr. (February 28, 1924 – July 22, 2019) was an American aerospace and NASA engineer who was instrumental in establishing the agency's Mission Control Center and shaping its organization and culture. His protégé Glynn Lunney said in 1998: "the Control Center today ... is a reflection of Chris Kraft".

Following his 1944 graduation from Virginia Polytechnic Institute and State University with a degree in aeronautical engineering, Kraft was hired by the National Advisory Committee for Aeronautics (NACA), the predecessor organization to the National Aeronautics and Space Administration (NASA). He worked for over a decade in aeronautical research and in 1958 joined the Space Task Group, a small team entrusted with the responsibility of putting America's first man in space. Assigned to the flight operations division, Kraft became NASA's first flight director. He was on duty during America's first crewed spaceflight, first crewed orbital flight, and first spacewalk. At the beginning of the Apollo program, Kraft retired as a flight director to concentrate on management and mission planning. In 1972, he became director of the Manned Spacecraft Center (later Johnson Space Center), following his mentor Robert R. Gilruth, and held the position until his retirement in 1982.