SOFIA test flight. SOFIA airborne observatory aircraft on a night-time flight over California in March 2013. The flight conducted verification and validation of aircraft and telescope systems in preparation for instrument commissioning. 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 slowly opened for observations to be obtained. SOFIA was jointly developed from 1996 by NASA and the German Aerospace Centre (DLR). The first observations took place in May 2010.