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