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The Neil Armstrong Operations and Checkout Building (O&C) (previously known as the Manned Spacecraft Operations Building) is a historic building on Merritt Island, Florida, United States. The five-story structure is in the Industrial Area of NASA's Kennedy Space Center. Its has twin-block facilities that include the crew quarter dormitories for astronauts, suit-up preparations prior to their flights, and the other is a large spacecraft workshop used for manufacturing and checking activities on crewed spacecraft. On January 21, 2000, it was added to the U.S. National Register of Historic Places. During planning and construction, it was known as the Operations and Checkout Building. When it was finished in 1964, it was renamed the Manned Spacecraft Operations Building and was used to process spacecraft in the Gemini and Apollo era. It was reverted back to the Operations and Checkout Building during the Shuttle program, known informally as the O&C. In 1965, a pair of altitude chambers were installed in the High Bay for testing the environmental and life support systems of both the Apollo Command/Service Module and Lunar Module at simulated altitudes of up to . Each chamber is high (with a clear working height of ) and an interior diameter of , were human-rated, and capable of reaching the maximum altitude (minimum pressure) in one hour. These were used by the prime and backup crews of all crewed missions, from the ill-fated Apollo 1 in October 1966, through to the Apollo-Soyuz Test Project in July 1975. During the 1980s and 90s the O&C building was used to house and test Spacelab science modules before their flights aboard the Space Shuttle. In the late 1990s and 2000s, some modules and trusses for the International Space Station were checked out in the building. On January 30, 2007, NASA held a ceremony to mark the transition of the building's high bay for use by the Constellation program. The building would serve as the final assembly facility for the Orion crew exploration vehicle.
