The Stratospheric Observatory for Infrared Astronomy (SOFIA) was an 80/20 joint project of NASA and the German Aerospace Center (DLR) to construct and maintain an airborne observatory. NASA awarded the contract for the development of the aircraft, operation of the observatory and management of the American part of the project to the Universities Space Research Association (USRA) in 1996. The DSI (Deutsches SOFIA Institut) managed the German parts of the project which were primarily science- and telescope-related. SOFIA's telescope saw first light on May 26, 2010. SOFIA was the successor to the Kuiper Airborne Observatory. During 10-hour, overnight flights, it observed celestial magnetic fields, star-forming regions, comets, nebulae, and the Galactic Center. Science flights have now concluded, after the landing of the 921st and last flight in the early morning of September 29, 2022. The project will continue to work with legacy data for a few years. On December 8, 2022, NASA announced that both SOFIA and the Boeing 747SP used to carry the telescope will be preserved and put on display at the Pima Air & Space Museum in Tucson, Arizona. Facility SOFIA was based on a Boeing 747SP wide-body aircraft that had been modified to include a large door in the aft fuselage that could be opened in flight to allow a diameter reflecting telescope access to the sky. This telescope was designed for infrared astronomy observations in the stratosphere at altitudes of about . SOFIA's flight capability allowed it to rise above almost all of the water vapor in the Earth's atmosphere, which blocks some infrared wavelengths from reaching the ground. At the aircraft's cruising altitude, 85% of the full infrared range was available. The aircraft could also travel above almost any point on the Earth's surface, allowing observation from the northern and southern hemispheres. Observing flights were flown three or four nights a week. The SOFIA Observatory was based at NASA's Armstrong Flight Research Center at Palmdale Regional Airport, California, while the SOFIA Science Center was based in Ames Research Center, in Mountain View, California. The telescope SOFIA uses a reflector telescope, which has an oversized, diameter primary mirror, as was common with most large infrared telescopes. The optical system uses a Cassegrain reflector design with a parabolic primary mirror and a remotely configurable hyperbolic secondary. In order to fit the telescope into the fuselage, the primary was shaped to an f-number as low as 1.3,