In August 1973, NASA and ESRO (now European Space Agency or ESA) signed a Memorandum of Understanding to build a science laboratory for use on Space Shuttle flights. Construction of Spacelab was started in 1974 by the ERNO (subsidiary of VFW-Fokker GmbH, after merger with MBB named MBB/ERNO, and part of EADS SPACE Transportation since 2003). The first lab module, LM1, was donated to NASA in exchange for flight opportunities for European astronauts. A second module, LM2, was bought by NASA for its own use from ERNO.

Approximately 4” Diameter