An example of satellite "spot beam" footprints with a reception
area of Northern Command (USNORTHCOM) and Central Command
(CENTCOM). This coverage is for US Air Force satellites F8, F9,
F10 and SATCOM KU2 as well as leased commercial satellites
Galaxy 10 and Telstar 11. These satellites were used to
transmit Video, Television and Internet data to remote locations
and ships that otherwise would not have that capability. These
maps were created for planning purposes as well as operations.
The ellipses/horseshoes indicate the location where
reception is available and the necessary antenna diameter for
receiving data. When searching for a satellite, it's very
important to know if the beam reaches your location.
The
footprint of a communications satellite is the ground area that
its transponders offer coverage, and determines the satellite
dish diameter required to receive each transponder's signal.
There is usually a different map for each transponder (or group
of transponders), as each may be aimed to cover different areas.
Footprint maps usually show either the estimated minimum
satellite dish diameter required or the signal strength in each
area measured in dBW.
A geosynchronous orbit (sometimes
abbreviated GSO) is an orbit around the Earth with an orbital
period of one sidereal day, intentionally matching the Earth's
sidereal rotation period (approximately 23 hours 56 minutes and
4 seconds).[1] The synchronization of rotation and orbital
period means that, for an observer on the surface of the Earth,
an object in geosynchronous orbit returns to exactly the same
position in the sky after a period of one sidereal day. Over the
course of a day, the object's position in the sky traces out a
path, typically in the form of an analemma, whose precise
characteristics depend on the orbit's inclination and
eccentricity.
A special case of geosynchronous orbit is
the geostationary orbit, which is a circular geosynchronous
orbit at zero inclination (that is, directly above the equator).
A satellite in a geostationary orbit appears stationary, always
at the same point in the sky, to ground observers. Popularly or
loosely, the term "geosynchronous" may be used to mean
geostationary.[2] Specifically, geosynchronous Earth orbit (GEO)
may be a synonym for geosynchronous equatorial orbit,[3] or
geostationary Earth orbit.[4] Communications satellites are
often given geostationary orbits, or close to geostationary, so
that the satellite antennas that communicate with them do not
have to move, but can be pointed permanently at the fixed
location in the sky where the satellite appears.
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