Satellites are commissioned and run by Satellite Operators. The major Satellite Operators include Intelsat, New Skies Satellites, SES-Americom/Panamsat, Eutelsat and Arabsat. Satellites are given alpha numeric identifiers by their operators for example, New Skies Satellite’s NSS 7, Intelsat’s IS10 and Panamsat’s Pas 1R.
Satellites are launched from earth using rockets, just like the space shuttle, and placed in an orbit around the earth. Communication satellites are placed in special circular orbits called geosynchronous orbits. In this orbit, a satellite will orbit the earth in 24 hours, the same time it takes the earth to complete one revolution about its axis. If the satellite is placed in an orbit precisely over the equator, the satellite will appear to be stationary in space when viewed from any point on earth. The orbit is then known as the geostationary orbit or Clarke Orbit, named after Arthur C Clarke, who first described the properties of such an orbit. This “stationary” property makes geostationary satellites useful for communication purposes as they enable one to have the VSAT dish fixed on earth and always pointed in the same direction. Otherwise, VSAT dishes would have to be movable to keep track of the satellite’s movement in space! We should at this point mention that sometimes, VSAT dishes have to be moveable and track a satellite’s movement in space. This happens in the special case of the Inclined Orbit, discussed a little later on.
The satellite stays in orbit and does not fall back to earth because of the effect of centrifugal forces as it revolves around the earth. The satellite in space also experiences other forces, such as gravitational pull from the sun, that tend to draw the satellite out of its orbit. This effect is countered by equipping satellites with small rockets which are periodically “fired” and burn a special propellant to produce gases. The gases expelled move the satellite just like a balloon filled with air will move if some of the air is expelled, in line with Newton’s third law (for every force, there is an equal and opposite force). These movements are small but help to keep the satellite on course in the orbit.
The propellant used by the rockets for course correction last 10 -15 years and determines the “useful” life of the satellite. Once the propellant is used up, the rockets can no longer be fired to return the satellite to its regular course and the satellite slowly drifts off course. Towards the end of the useful life of the satellite, Satellite Operators may prolong the life of the satellite by conserving the propellant and deliberately allowing the satellite to slowly drift off course. For geostationary orbits, the satellite’s orbit changes from a circle in the same plane as the equator to an ellipse inclined to the plane of the earth’s equator and moving along a widening figure 8-like path within the orbit along a north-south axis. The satellite is thus said to be in “inclined orbit.”
The satellite in inclined orbit can still be used for communications provided that the dish on earth is movable and can track the irregular movement of the satellite. This can be accomplished by equipping the dish with an automatic tracking system that steers the dish and keeps it aligned with the satellite.