A modified and unusual short-body Boeing 747SP with a giant door in the rear fuselage, just behind the wings, a door nearly as wide as two-car garage. This airborne observatory is SOFIA, the Stratospheric Observatory For Infrared Astronomy.
SOFIA is a joint creation of NASA, which oversaw the extensive modification of the aircraft, and the German Aerospace Center DLR, which managed the construction of the telescope, the largest ever borne aloft.
The 2.7-meter telescope is bigger than NASA’s famed 2.4-meter Hubble Space Telescope, and even bigger than the 100-inch (2.5-meter) Hooker reflector atop Mount Wilson, California, which reigned as the largest telescope in the world from 1917 until 1948 (when it was surpassed by the 200-inch Hale on Palomar Mountain in San Diego County).
An aircraft flying in the stratosphere, is above 99.8 percent of the vapor. The stratosphere’s dry cold (as low as –60 degrees Fahrenheit) can keep the entire structure and primary mirror at cryogenic temperatures without condensation or frost.