(29d) Satellites with Commercial Missions

This groups includes about 200 communication satellites ("comsats") scattered in synchronous orbits above the Earth's equator. At a distance of 6. 6 Earth radii (42,000 km or 26,000 miles), these satellite make one orbit per day, (sidereal day of 23 h 56 min--see here) and therefore as the Earth turns, they always stay above the same ground station. Comsats have become essential to the relaying of television broadcasts, long distance telephone connections and computer communications: if you are receiving this from the world-wide web (especially if you are outside the US) this document might well have been routed to you through one of them.

NASA maintains several communication satellites as data links to other satellites, an arrangement found more economical than the use of tracking stations on the ground. In addition, networks of low-altitude communication satellites (e.g. "Iridium", a system of 66 spacecraft, plus spares) are being deployed for use by cellular telephones.

Some beneficial satellites were already listed under different classifications: weather satellites, like those of the GOES series, and those which scan the Sun and the "solar wind" for activity affecting "space weather" inside the magnetosphere.

    For a detailed article about this technology, see "Satellite-Guided Munitions" by Michael Puttré, p. 66-73 in "Scientific American," issue of February 2003.