NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA) is being developed as a world-class observatory complementing the Hubble Space Telescope. The observatory, which features a German-built 98.4-inch (2.5 meter) diameter infrared telescope weighing 20 metric tons mounted in a highly-modified Boeing 747SP aircraft, has begun its flight test phase in a joint program by NASA and DLR Deutsches Zentrum fur Luft und Raumfahrt (German Aerospace Center). Major aircraft modifications and installation of the telescope was performed by L-3 Communications Integrated Systems facility at Waco, Texas. Systems integration and flight test operations are being conducted at NASA's Dryden Flight Resarch Center at Edwards Air Force Base, Calif. SOFIA's science and mission operations are managed jointly by the Universities Space Research Association (USRA) and the Deutsches SOFIA Institut (DSI), and are based at NASA's Ames Research Center at Moffett Field near San Jose, Calif. Once operational in the 2009-2010 period, SOFIA will be the world's primary infrared observatory during a mission lasting up to 20 years, as well as an outstanding laboratory for developing and testing instrumentation and detector technology.