In the early morning of 15 November 2005, the unmanned Altair aircraft returned to Gray Butte Airfield, north of Los Angeles, Calif., after completing an 18.4-hour mission over the eastern Pacific Ocean. The flight was the last in a series undertaken by the U.S. National Oceanic and Atmospheric Administration (NOAA) in its Unmanned Aircraft System (UAS) Demonstration Project. The successful flight series has helped start the era of unmanned flights in service of environmental goals. Altair cruised at altitudes in the lower stratosphere (13 kilo-meters; ∼43,000 feet), collecting atmospheric data with a 140-kilogram payload of both remote and in situ instruments.