SOFIA airborne observatory aircraft during a test flight. SOFIA is the Stratospheric Observatory for Infrared Astronomy. It is a 2.5-metre infrared telescope that is flown in its 747SP aircraft to the stratosphere, some 10-50 kilometres above sea level. This allows the detection of infrared light that is normally blocked by water vapour lower in the atmosphere. Here, the observation door in the fuselage is partially open. SOFIA was jointly developed from 1996 by NASA and the German Aerospace Centre (DLR). The first observations took place in May 2010.