A small space station built by the European Space Agency (ESA) which was carried in the cargo bay of the US space shuttle, returning to Earth with the shuttle. Spacelab consisted of a pressurized module in which astronauts worked, and a series of pallets, open to the vacuum of space, on which equipment was mounted. Spacelab was used for astronomy, Earth observation, and experiments utilizing the conditions of weightlessness and vacuum in orbit.

The first Spacelab mission lasted from 28 November to 8 December 1983. Three other missions were flown between 1983 and 1985. The first crewed mission managed by a nation other than the USA or USSR was a German Spacelab mission, D1 Spacelab. It carried a record crew of eight and lasted from 30 October to 6 November 1985 aboard the space shuttle Challenger. Spacelab life sciences missions were flown in June 1991 and October 1993; a life science and microgravity mission was flown in June–July 1996. Spacelab was used in 25 shuttle flights, but was finally decommissioned in 1998.

http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/spacelab.html#spacelab Space shuttle reference manual with a chapter describing in detail the make-up and operation of the Spacelab pressurized experiment module.