| Introduction and Brief History of
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| | satellite revolves around the earth at a
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| Satellites
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| | constant speed once per day over the
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| A satellite is any object that orbits
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| | equator. The geostationary orbit is
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| another object (which is known as its
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| | useful for communications applications
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| primary). All masses that are part of the
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| | because ground based antennae, which must
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| solar system, including the Earth, are
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| | be directed toward the satellite, can
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| satellites either of the Sun, or
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| | operate effectively without the need for
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| satellites of those objects, such as the
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| | expensive equipment to track the
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| Moon. It is not always a simple matter to
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| | satellite's motion. Especially for
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| decide which is the 'satellite' in a pair
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| | applications that require a large number
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| of bodies. Because all objects exert
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| | of ground antennae (such as direct TV
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| gravity, the motion of the primary object
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| | distribution), the savings in ground
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| is also affected by the satellite. If two
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| | equipment can more than justify the extra
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| objects are ufficiently similar in mass,
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| | cost and onboard complexity of lifting a
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| they are generally referred to as a
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| | satellite into the relatively high
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| binary system rather than a primary
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| | geostationary orbit.
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| object and satellite. The general
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| | The concept of the geostationary
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| criterion for an object to be a satellite
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| | communications satellite was first
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| is that the center of mass of the two
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| | proposed by Arthur C. Clarke, building on
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| objects is inside the primary object. In
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| | work by Konstantin Tsiolkovsky and on the
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| popular usage, the term 'satellite'
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| | 1929 work by Herman Potočnik
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| normally refers to an artificial
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| | (writing as Herman Noordung) Das Problem
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| satellite (a man-made object that orbits
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| | der Befahrung des Weltraums - der
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| the Earth or another body).
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| | Raketen-motor. In October 1945 Clarke
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| In May, 1946, the Preliminary Design of
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| | published an article titled
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| an Experimental World-Circling Spaceship
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| | "Extra-terrestrial Relays" in the British
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| stated, "A satellite vehicle with
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| | magazine Wireless World. The article
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| appropriate instrumentation can be
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| | described the fundamentals behind the
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| expected to be one of the most potent
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| | deployment of artificial satellites in
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| scientific tools of the Twentieth
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| | geostationary orbits for the purpose of
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| Century. The achievement of a satellite
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| | relaying radio signals. Thus Arthur C.
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| craft would produce repercussions
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| | Clarke is often quoted as being the
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| comparable to the explosion of the atomic
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| | inventor of the communications satellite.
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| bomb..."
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| | The first geostationary communications
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| The space age began in 1946, as
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| | satellite was Anik 1, a Canadian
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| scientists began using captured German
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| | satellite launched in 1972. The United
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| V-2 rockets to make measurements in the
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| | States launched their own geostationary
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| upper atmosphere. Before this period,
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| | communication satellites afterward, with
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| scientists used balloons that went up to
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| | Western Union launching their Westar 1
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| 30 km and radio waves to study the
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| | satellite in 1974, and RCA Americom
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| ionosphere. From 1946 to 1952,
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| | (later GE Americom, now SES Americom)
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| upper-atmosphere research was conducted
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| | launching Satcom 1 in 1975. It was
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| using V-2s and Aerobee rockets. This
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| | Satcom 1 that was instrumental in helping
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| allowed measurements of atmospheric
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| | early cable TV channels such as WTBS (now
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| pressure, density, and temperature up to
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| | TBS Superstation), HBO, CBN (now ABC
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| 200 km. The U.S. had been considering
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| | Family), and The Weather Channel become
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| launching orbital satellites since 1945
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| | successful, because these channels
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| under the Bureau of Aeronautics of the
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| | distributed their programming to all of
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| United States Navy. The Air Force's
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| | the local cable TV headends using the
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| Project RAND eventually released the
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| | satellite. Additionally, it was the first
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| above report, but did not believe that
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| | satellite used by broadcast TV networks
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| the satellite was a potential military
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| | in the United States, like ABC, NBC, and
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| weapon; rather they considered it to be a
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| | CBS, to distribute their programming to
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| tool for science, politics, and
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| | all of their local affiliate stations.
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| propaganda. Following pressure by the
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| | The reason that Satcom 1 was so widely
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| American Rocket Society, the National
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| | used is that it had twice the
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| Science Foundation, and the International
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| | communications capacity of Westar 1 (24
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| Geophysical Year, military interest
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| | transponders as opposed to Westar 1's
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| picked up and in early 1955 the Air Force
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| | 12), which resulted in lower transponder
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| and Navy were working on Project Orbiter,
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| | usage costs.
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| which involved using a Jupiter C rocket
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| | By 2000 Hughes Space and Communications
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| to launch a small satellite called
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| | (now Boeing Satellite Systems) had built
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| Explorer 1 on January 31, 1958.
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| | nearly 40 percent of the satellites in
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| On July 29, 1955, the White House
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| | service worldwide. Other major satellite
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| announced that the U.S. intended to
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| | manufacturers include Space Systems
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| launch satellites by the spring of 1958.
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| | Loral, Lockheed Martin (owns former RCA
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| This became known as Project Vanguard. On
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| | Astro Electronics/GE Astro Space
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| July 31, the Soviets announced that they
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| | business), Northrop Grumman, Alcatel
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| intended to launch a satellite by the
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| | Space and EADS Astrium.
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| fall of 1957 and on October 4, 1957
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| | (b) Low-Earth-orbiting satellites: A low
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| Sputnik I was launched into orbit, which
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| | Earth orbit typically is a circular orbit
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| triggered the Space Race between the two
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| | about 150 kilometers above the earth's
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| nations.
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| | surface and, correspondingly, a period
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| The largest artificial satellite
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| | (time to revolve around the earth) of
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| currently orbiting the earth is the
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| | about 90 minutes. Because of their low
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| International Space Station, which can
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| | altitude, these satellites are only
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| sometimes be seen with the unaided human
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| | visible from within a radius of roughly
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| eye.
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| | 1000 kilometers from the sub-satellite
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| Types of satellites
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| | point. In addition, satellites in low
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| · Astronomical satellites: These are
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| | earth orbit change their position
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| satellites used for observation of
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| | relative to the ground position quickly.
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| distant planets, galaxies, and other
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| | So even for local applications, a large
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| outer space objects.
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| | number of satellites are needed if the
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| · Communications satellites: These are
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| | mission requires uninterrupted
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| artificial satellites stationed in space
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| | connectivity.
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| for the purposes of telecommunications
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| | Low earth orbiting satellites are less
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| using radio at microwave frequencies.
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| | expensive to position in space than
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| Most communications satellites use
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| | geostationary satellites and, because of
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| geosynchronous orbits or
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| | their closer proximity to the ground,
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| near-geostationary orbits, although some
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| | require lower signal strength. So there
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| recent systems use low Earth-orbiting
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| | is a trade off between the number of
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| satellites.
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| | satellites and their cost. In addition,
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| · Earth observation satellites are
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| | there are important differences in the
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| satellites specifically designed to
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| | onboard and ground equipment needed to
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| observe Earth from orbit, similar to
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| | support the two types of missions.
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| reconnaissance satellites but intended
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| | A group of satellites working in concert
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| for non-military uses such as
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| | thus is known as a satellite
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| environmental monitoring, meteorology,
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| | constellation. Two such constellations
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| map making etc. (See especially Earth
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| | which were intended for provision for
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| Observing System.)
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| | hand held telephony, primarily to remote
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| · Navigation satellites are satellites
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| | areas, were the Iridium and Globalstar.
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| which use radio time signals transmitted
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| | The Iridium system has 66 satellites.
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| to enable mobile receivers on the ground
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| | Another LEO satellite constellation, with
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| to determine their exact location. The
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| | backing from Microsoft entrepreneur Paul
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| relatively clear line of sight between
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| | Allen, was to have as many as 720
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| the satellites and receivers on the
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| | satellites. It is also possible to offer
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| ground, combined with ever-improving
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| | discontinuous coverage using a low Earth
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| electronics, allows satellite navigation
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| | orbit satellite capable of storing data
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| systems to measure location to accuracies
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| | received while passing over one part of
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| on the order of a few metres in real
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| | Earth and transmitting it later while
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| time.
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| | passing over another part. This will be
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| · Reconnaissance satellites are Earth
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| | the case with the CASCADE system of
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| observation satellite or communications
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| | Canada's CASSIOPE communications
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| satellite deployed for military or
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| | satellite.
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| intelligence applications. Little is
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| | (c) Molniya satellites: As mentioned,
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| known about the full power of these
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| | geostationary satellites are constrained
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| satellites, as governments who operate
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| | to operate above the equator. As a
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| them usually keep information pertaining
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| | consequence, they are not always suitable
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| to their reconnaissance satellites
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| | for providing services at high latitudes:
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| classified.
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| | for at high latitudes a geostationary
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| · Solar power satellites are proposed
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| | satellite may appear low on (or even
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| satellites built in high Earth orbit that
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| | below) the horizon, affecting
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| use microwave power transmission to beam
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| | connectivity and causing multipathing
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| solar power to very large antenna on
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| | (interference caused by signals
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| Earth where it can be used in place of
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| | reflecting off the ground into the ground
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| conventional power sources.
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| | antenna). The first satellite of Molniya
|
| · Space stations are man-made structures
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| | series was launched on April 23, 1965 and
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| that are designed for human beings to
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| | was used for experimental transmission of
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| live on in outer space. A space station
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| | TV signal from Moscow uplink station to
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| is distinguished from other manned
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| | downlink stations, located in Russian Far
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| spacecraft by its lack of major
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| | East, in Khabarovsk, Magadan and
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| propulsion or landing facilities -
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| | Vladivostok. In November of 1967 Soviet
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| instead, other vehicles are used as
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| | engineers created a unique system of
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| transport to and from the station. Space
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| | national TV network of satellite
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| stations are designed for medium-term
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| | television, called Orbita that was based
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| living in orbit, for periods of weeks,
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| | on Molniya satellites.
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| months, or even years.
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| | Molniya orbits can be an appealing
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| · Weather satellites are satellites that
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| | alternative in such cases. The Molniya
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| primarily are used to monitor the weather
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| | orbit is highly inclined, guaranteeing
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| and/or climate of the Earth.
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| | good elevation over selected positions
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| · Miniaturized satellites are satellites
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| | during the northern portion of the orbit.
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| of unusually low weights and small sizes.
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| | (Elevation is the extent of the
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| New classifications are used to
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| | satellite's position above the horizon.
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| categorize these satellites:
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| | Thus a satellite at the horizon has zero
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| minisatellite (500-200 kg),
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| | elevation and a satellite directly
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| microsatellite (below 200 kg),
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| | overhead has elevation of 90 degrees).
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| nanosatellite (below 10 kg).
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| | Furthermore, the Molniya orbit is so
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| Orbit types
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| | designed that the satellite spends the
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| Many times satellites are characterized
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| | great majority of its time over the far
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| by their orbit. Although a satellite may
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| | northern latitudes, during which its
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| orbit at almost any height, satellites
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| | ground footprint moves only slightly. Its
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| are commonly categorized by their
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| | period is one half day, so that the
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| altitude:
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| | satellite is available for operation over
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| · Low Earth Orbit (LEO: 200 - 1200km
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| | the targeted region for eight hours every
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| above the Earth's surface)
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| | second revolution. In this way a
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| · Medium Earth Orbit (ICO or MEO: 1200 -
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| | constellation of three Molniya satellites
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| 35286 km)
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| | (plus in-orbit spares) can provide
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| · Geosynchronous Orbit (GEO: 35786 km
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| | uninterrupted coverage.
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| above Earth's surface) and Geostationary
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| | Molniya satellites are typically used for
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| Orbit ( zero inclination geosynchronous
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| | telephony and TV services over Russia.
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| orbit). These orbits are of particular
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| | Another application is to use them for
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| interest for communication satellites
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| | mobile radio systems (even at lower
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| and will be discussed in detail later.
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| | latitudes) since cars traveling through
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| · High Earth Orbit (HEO: above 35786 km)
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| | urban areas need access to satellites at
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| The following orbits are special orbits
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| | high elevation in order to secure good
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| that are also used to categorize
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| | connectivity, e.g. in the presence of
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| satellites:
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| | tall buildings.
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| · Molniya orbits: Is a class of a highly
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| | Applications of Satellites
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| elliptic orbit. A satellite placed in
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| | (a) Telephony: One of the major
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| this orbit spends most of its time over a
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| | applications of a communication
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| designated area of the earth, a
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| | satellite is in provision of long
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| phenomenon known as apogee dwell. Molniya
| |
| | distance telephone services. The
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| orbits are named after a series of Soviet
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| | connectivity is through frequency
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| Russian Molniya communications satellites
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| | division multiple access (FDMA) or time
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| that have been using this class of orbits
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| | division multiple access(TDMA)
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| since the mid 1960s.
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| | predominantly. Telephone subscribers can
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| · Heliosynchronous or sun-synchronous
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| | be connected through a network of
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| orbit: A heliosynchronous orbit, or more
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| | exchanges which are in turn connected to
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| commonly a sun-synchronous orbit is an
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| | satellite earth stations which uplink the
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| orbit in which an object always passes
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| | traffic to satellite for further
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| over any given point of the Earth's
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| | processing.
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| surface at the same local solar time.
| |
| | (b) Television and Radio: There are
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| This is a useful characteristic for
| |
| | two types of satellites used for
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| satellites that image the earth's surface
| |
| | television and radio:
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| in visible or infrared wavelengths (e.g.
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| | (i) Direct Broadcast Satellite (DBS): A
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| weather, spy and remote sensing
| |
| | direct broadcast satellite is a
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| satellites).
| |
| | communications satellite that transmits
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| · Polar orbit : A satellite in a polar
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| | to small DBS satellite dishes (usually
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| orbit passes above or nearly above both
| |
| | 18" to 24" in diameter). Direct broadcast
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| poles of the planet (or other celestial
| |
| | satellites generally operate in the upper
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| body) on each revolution.
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| | portion of the Ku band. DBS technology is
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| · Hohmann transfer orbit: For this
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| | used for DTH-oriented (Direct-To-Home)
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| particular orbit type, it is more common
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| | satellite TV services, such as DirecTV
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| to identify the satellite as a
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| | and Dish Network in the United States,
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| spacecraft. In astronautics and aerospace
| |
| | ExpressVu in Canada, and Sky Digital in
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| engineering, the Hohmann transfer orbit
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| | the UK.
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| is an orbital maneuver that moves a
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| | (ii) Fixed Service Satellite (FSS): Use
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| spacecraft from one orbit to another.
| |
| | the C band, and the lower portions of the
|
| · Supersynchronous orbit or drift orbit
| |
| | Ku bands. They are normally used for
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| : orbit above GEO. Satellites will drift
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| | broadcast feeds to and from television
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| in a westerly direction.
| |
| | networks and local affiliate stations
|
| · Subsynchronous orbit or drift orbit:
| |
| | (such as program feeds for network and
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| orbits close to but below GEO. Used for
| |
| | syndicated programming, live shots, and
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| satellites undergoing station changes in
| |
| | backhauls), as well as being used for
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| an eastern direction.
| |
| | distance learning by schools &
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| Communication Satellites
| |
| | universities, business television (BTV),
|
| A communications satellite (sometimes
| |
| | videoconferencing, and general commercial
|
| abbreviated to comsat) is an artificial
| |
| | telecommunications. FSS satellites are
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| satellite stationed in space for the
| |
| | also used to distribute national cable
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| purposes of telecommunications. Modern
| |
| | channels to cable TV headends. FSS
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| communications satellites use
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| | satellites differ from DBS satellites in
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| geosynchronous orbits, Molniya orbits or
| |
| | that they have a lower RF power output
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| low Earth orbits.
| |
| | than the latter, requiring a much larger
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| For fixed services, communications
| |
| | dish for reception (3 to 8 feet in
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| satellites provide a technology
| |
| | diameter for Ku band, and 12 feet on up
|
| complementary to that of fiber optic
| |
| | for C band). FSS satellite technology was
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| submarine communication cables. For
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| | also originally used for DTH satellite TV
|
| mobile applications, such as
| |
| | from the late 1970s to the early 1990s in
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| communications to ships and planes
| |
| | the USA in the form of TVRO (TeleVision
|
| satellite based communicationis only the
| |
| | Receive Only) receivers and dishes
|
| viable means of communications as
| |
| | (a.k.a. big-dish, or more pejoratively
|
| application of other technologies, such
| |
| | known as big ugly dish, systems). It was
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| as cable, are impractical or impossible.
| |
| | also used in its Ku band form for the
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| Early missions: The origin of satellite
| |
| | now-defunct Primestar satellite TV
|
| communication can be traced to an article
| |
| | service.
|
| written by Arthur C. Clarke in 1945. He
| |
| | (c) Mobile satellite technologies:
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| suggested that a radio relay satellite in
| |
| | Initially available for broadcast to
|
| an equatorial orbit with a period of 24
| |
| | stationary TV receivers, by 2004 popular
|
| hours would remain stationary with
| |
| | mobile direct broadcast applications made
|
| respect to earth's surface and can be
| |
| | their appearance with that arrival of two
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| used for long-range radio communication,
| |
| | satellite radio systems in the United
|
| as it will over come the limitations
| |
| | States: Sirius and XM Satellite Radio
|
| imposed by earth curvature. Sputnik 1,
| |
| | Holdings. Some manufacturers have also
|
| The world's first artificial (non
| |
| | introduced special antennas for mobile
|
| communication) satellite, was launched on
| |
| | reception of DBS television. Using GPS
|
| October 4, 1957. The first satellite to
| |
| | technology as a reference, these antennas
|
| relay communications was Project SCORE in
| |
| | automatically re-aim to the satellite no
|
| 1958, which used a tape recorder to store
| |
| | matter where or how the vehicle (that the
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| and forward voice messages. It was used
| |
| | antenna is mounted on) is situated. These
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| to send a Christmas greeting to the world
| |
| | mobile satellite antennas are popular
|
| from President Eisenhower. NASA launched
| |
| | with some recreational vehicle owners.
|
| an Echo satellite in 1960. This 100-foot
| |
| | Such mobile DBS antennas are also used by
|
| aluminized Mylar balloon served as a
| |
| | JetBlue Airways for DirecTV (supplied by
|
| passive reflector for radio
| |
| | LiveTV, a subsidiary of JetBlue), which
|
| communications. Courier 1B, (built by
| |
| | passengers can view on-board on LCD
|
| Philco) also was launched in 1960, was
| |
| | screens mounted in the seats.
|
| the world's first active repeater
| |
| | (d) Amateur radio: Amateur radio
|
| satellite. Given below are the details of
| |
| | operators have access to the OSCAR
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| milestones in satellite communcation
| |
| | satellites that have been designed
|
| history: -
| |
| | specifically to carry amateur radio
|
| · Herman Potocnik - describes a space
| |
| | traffic. Most such satellites operate as
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| station in geosynchronous orbit - 1928
| |
| | space borne repeaters, and are generally
|
| · Arthur C. Clarke - proposes a station
| |
| | accessed by amateurs equipped with UHF or
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| in geosynchronous orbit to relay
| |
| | VHF radio equipment and highly
|
| communications and broadcast television -
| |
| | directional antennas such as Yagis or
|
| 1945
| |
| | dish antennas. Due to the limitations of
|
| · Project SCORE - first communications
| |
| | ground-based amateur equipment, most
|
| satellite - 1958
| |
| | amateur satellites are launched into
|
| · Echo I - first passive reflector
| |
| | fairly low Earth orbits, and are designed
|
| satellite - August 1960
| |
| | to deal with only a limited number of
|
| · Courier 1B - first active repeater
| |
| | brief contacts at any given time. Some
|
| satellite - October 1960
| |
| | satellites also provide data-forwarding
|
| · Telstar - the first active direct
| |
| | services using the X.25 or similar
|
| relay satellite designed to transmit
| |
| | protocols.
|
| television and high-speed data
| |
| | Satellite Broadband Services: In recent
|
| communications. Telstar was placed in an
| |
| | years, satellite communication technology
|
| elliptical orbit (completed once every 2
| |
| | has been used as a means to connect to
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| hours and 37 minutes), rotating at a 45°
| |
| | the Internet via broadband data
|
| angle above the equator. July 1962
| |
| | connections. This is can be very useful
|
| · Syncom - first communications
| |
| | for users to test who are located in very
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| satellite in geosynchronous orbit. Syncom
| |
| | remote areas, and can't access a wireline
|
| 2 revolved around the earth once per day
| |
| | broadband or dialup connection.
|
| at constant speed, but because it still
| |
| | Countries with satellite launch
|
| had north-south motion special equipment
| |
| | capability
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| was needed to track it. 1963
| |
| | This list includes counties with an
|
| · OSCAR-III - first amateur radio
| |
| | independent capability to place
|
| communications satellite - March 1965
| |
| | satellites in orbit, including production
|
| · Molniya - first Soviet communication
| |
| | of the necessary launch vehicle. Many
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| satellite, highly elliptic orbit -
| |
| | more countries have built satellites that
|
| October 1965
| |
| | were launched with the aid of others. The
|
| · Early Bird - INTELSAT's first
| |
| | French and British capabilities are now
|
| satellite for commercial service - April
| |
| | subsumed by the European Union under the
|
| 1965
| |
| | European Space Agency.
|
| · Orbita - first national TV network
| |
| | First launch by country
|
| based on satellite television - November
| |
| | Country Year of first launch First
|
| 1967
| |
| | satellite
|
| · Anik 1 - the first national satellite
| |
| | Russia 1957 "Sputnik
|
| television system, Canada, - 1973
| |
| | 1"
|
| · Westar 1, the USA's first
| |
| | United States 1958
|
| geosynchronous communications satellite -
| |
| | "Explorer 1"
|
| April 1974
| |
| | France 1965
|
| · Ekran - first serial Direct-To-Home TV
| |
| | "Asterix"
|
| communication satellite 1976
| |
| | Japan 1970
|
| · Palapa A1 - first Indonesia
| |
| | "Osumi"
|
| communications satellite - July 8 1976
| |
| | China 1970
|
| · TDRSS - first satellite designed to
| |
| | "Dong Fang Hong I"
|
| provide communications relay services for
| |
| | United Kingdom 1971
|
| other spacecraft. - 1983
| |
| | "Prospero X-3"
|
| · Mars Global Surveyor - first
| |
| | European Union 1979
|
| communications satellite in orbit around
| |
| | "Ariane 1"
|
| another planet (Mars) - 1997
| |
| | India 1980
|
| · Cassini spacecraft relays to Earth
| |
| | "Rohini"
|
| images from the Huygens probe as it lands
| |
| | Israel 1988
|
| on Saturn's moon, Titan, the longest
| |
| | "Ofea 1"
|
| relay to date. -- January 14, 2005
| |
| | Iran 2005
|
| Depending on the need the communication
| |
| | "Sina 1"
|
| satellites can be placed in various types
| |
| | In 1998, North Korea claimed to have
|
| of orbits. We discuss few common types: -
| |
| | launched a satellite, but this was never
|
| (a) Geostationary orbits Satellites: A
| |
| | confirmed, and widely believed to be a
|
| satellite in a geostationary orbit
| |
| | cover for the test launch of the
|
| appears to be in a fixed position to an
| |
| | Taepodong-1 missile over Japan (See
|
| earth-based observer. A geostationary
| |
| | Kwangmyongsong).
|
