The space shuttle was initially used to deploy satellites in orbit; to carry scientific experiments such as Spacelab, a modular arrangement of experiments installed in the shuttle's cargo bay; and to carry out military missions. As the program has matured, the space shuttle also has been used to service and repair orbiting satellites and to retrieve and return to the earth previously deployed spacecraft.

The space shuttle carries a wide range of equipment, known as the payload, into space, ranging from communication, military, and astronomical satellites; space experiments for studying the apparent weightlessness (called "microgravity") experienced aboard a shuttle flight; and human experimental facilities. Often, NASA collaborates with other countries by allowing them to use shuttle cargo space for special projects.

The space shuttle is designed to leave the earth as a vertically launched rocket weighing up to 2.0 million kg (4.5 million lb) with 3 million kg (7 million lb) of thrust from its multiple propulsion systems. The orbiter segment returns from space—withstanding the intense heat when entering the earth's atmosphere. Flown by the shuttle crew much like an aircraft, the shuttle lands horizontally on a conventional airport runway.

The crew of the shuttle is an integral part of the system and is critical to the success of each mission. The flight crew is led by the commander and backed up by the pilot—both are professional astronauts and proven pilots with extensive space systems and operations training. Their primary responsibility is to fly the shuttle as a launch vehicle, spacecraft, and aircraft.