NASA is developing the Stratospheric Observatory for Infrared Astronomy - or SOFIA - as a world-class airborne observatory that will complement the Hubble, Spitzer, Herschel and James Webb space telescopes and major Earth-based telescopes. SOFIA features a German-built 100-inch (2.5 meter) diameter far-infrared telescope weighing 20 tons mounted in the rear fuselage of a highly modified Boeing 747SP aircraft. It is one of the premier space science programs of NASA's Science Mission Directorate.