The building of Fermi-LAT

The Large Area Telescope (LAT) instrument on the Fermi Gamma ray Space Telescope mission was inspired by the breadth of discoveries in high energy gamma ray sky by the EGRET instrument on the Compton Gamma Ray Observatory. Founded in the new technologies and capabilities in high energy particle physics detectors, the first studies for the LAT concept were begun in 1992 and the foundations of the LAT international collaboration, bringing together the high energy particle physics community and astrophysics community, were established shortly thereafter. This paper reviews the evolution of the LAT design from concept to launch and attempts to highlight the successes, problems and lessons learned along the way.