Navigational Satellites

Navigational satellites are very useful pieces of space equipment. They provide the Global Positioning System (GPS) network, which enables pilots, sailors, drivers, and hikers to fix positions almost anywhere on the globe with pin­point accuracy. Developed by the U. S. Department of Defense as NAVSTAR (Navigation Satellite Timing and Ranging Global Positioning System), the GPS uses at least twenty-four satel­lites to make sure that at least four are always within the line of sight of a nav­igator on the ground or ocean. One early navigation satellite, Transit 4A, was the first satellite to carry a small nuclear power plant.

Earth Observation and Weather Satellites

Earth observation (environmental) satel­lites are used to monitor changes in the environment such as melting ice caps, deforestation, and desertification. Earth observation satellites are normally launched into Sun-synchronous polar orbits so that they can survey the entire globe. They can scan for minerals, water, and other resources and record land use