An area of a spacecraft used to store satellites, payloads, and other equipment. On the space shuttle, the area can be viewed from the crew station through two large windows, and is 18 m in length and 4.6 m in diameter, taking up most of the shuttle's fuselage. It is large enough to accommodate five satellites or major parts of the Spacelab laboratory.

The cargo bay has two large doors running along its length. When they are open, giant cooling radiators on their interior sides dissipate heat generated by the shuttle's electrical systems.