Landsat is the name applied since 1974 to a program of unmanned satellites whose main objective is the study of the surface of the Earth.
The Landsat program includes seven satellites. Before 1974 the program was known as the ERTS (Earth Resources Technology Satellite). The satellites were launched in 1972, 1975, 1978, 1982, 1984, 1993 (failed), and 1999 (Landsat 7). Two of them, Landsat 5 and 7, are still active. The missions and commercialization of results of these civilian satellites have generally been managed by agencies of the US Government (NASA, NOAA and the US Geological Survey) although between 1984 and 2001 a private company was contracted for the purpose (NASA, 2010).
The orbit of Landsat satellites is Sun-synchronous near polar at an altitude of 918 km for Landsat 1, 2, 3 and 705 km for the remaining satellites. The spacecraft completes just over 14 orbits per day, covering the entire Earth between 81°N and S latitude every 18 days for...