An area of a spacecraft used to house permanent equipment or to carry temporary scientific equipment. A space shuttle has three avionics equipment bays (two forward, one aft) on its mid-deck and an equipment bay below the mid-deck floor that houses the main components of the waste management and air-revitalization systems.

Other examples are the International Ultraviolet Explorer (IUE) satellite with a main equipment bay at its base for most of the high-powered electronic equipment, and the Ulysses space probe's upper equipment bay that holds its reaction control system. The Apollo 11 lunar module used its equipment bay to store the early Apollo scientific experiments package (EASEP).