The Stratospheric Observatory for Infrared Astronomy (SOFIA) is an airborne infrared observatory that is the successor to the Kuiper Airborne Observatory (KAO). It is a Boeing 747 airliner that has been modified to carry a 100-inch (2.5-meter) diameter telescope, and it operates at altitudes of about 41,000 feet (12,500 meters). SOFIA is a joint project of NASA and the German Aerospace Center (Deutschen Zentrums für Luft, or DLR). It made its first test flight on April 26, 2007, and started science flights in 2010.