Aerial remote sensing currently operates from altitudes of about 500 meters to 20 kilometers (km) with the latter being the domain of aircraft such as the U2 for national security purposes. The range of operation for most spacecraft and satellite remote sensing is about 250 km to 1000 km with satellites close to the 1000 km level. Some remote sensing satellites also operate in geostationary orbit at 36,000 km. By the nature of that orbit, these satellites remain over the same place on Earth at all times.