Introduction and Brief History of Satellites and communication Satellites

Introduction and Brief History of Satellites

A satellite is any object that orbits someone else object (which is known as its primary). All masses that are part of the solar system, along with the Earth, are satellites whether of the Sun, or satellites of those objects, such as the Moon. It is not all the time a straightforward matter to determine which is the 'satellite' in a pair of bodies. Because all objects exert gravity, the appeal of the original object is also affected by the satellite. If two objects are ufficiently similar in mass, they are ordinarily referred to as a binary law rather than a original object and satellite. The general criterion for an object to be a satellite is that the center of mass of the two objects is inside the original object. In favorite usage, the term 'satellite' ordinarily refers to an artificial satellite (a man-made object that orbits the Earth or someone else body).

In May, 1946, the preliminary originate of an Experimental World-Circling Spaceship stated, "A satellite vehicle with thorough instrumentation can be startling to be one of the most potent scientific tools of the Twentieth Century. The achievement of a satellite craft would produce repercussions comparable to the explosion of the atomic bomb..."

The space age began in 1946, as scientists began using captured German V-2 rockets to make measurements in the upper atmosphere. Before this period, scientists used balloons that went up to 30 km and radio waves to study the ionosphere. From 1946 to 1952, upper-atmosphere study was conducted using V-2s and Aerobee rockets. This allowed measurements of atmospheric pressure, density, and climatic characteristic up to 200 km. The U.S. Had been considering launching orbital satellites since 1945 under the Bureau of Aeronautics of the United States Navy. The Air Force's project Rand finally released the above report, but did not believe that the satellite was a possible military weapon; rather they determined it to be a tool for science, politics, and propaganda. Following pressure by the American Rocket Society, the National Science Foundation, and the International Geophysical Year, military interest picked up and in early 1955 the Air Force and Navy were working on project Orbiter, which complicated using a Jupiter C rocket to start a small satellite called Explorer 1 on January 31, 1958.

On July 29, 1955, the White House announced that the U.S. Intended to start satellites by the spring of 1958. This became known as project Vanguard. On July 31, the Soviets announced that they intended to start a satellite by the fall of 1957 and on October 4, 1957 Sputnik I was launched into orbit, which triggered the Space Race in the middle of the two nations.

The largest artificial satellite currently orbiting the earth is the International Space Station, which can sometimes be seen with the unaided human eye.

Types of satellites

· Astronomical satellites: These are satellites used for notice of distant planets, galaxies, and other outer space objects.

· Communications satellites: These are artificial satellites stationed in space for the purposes of telecommunications using radio at microwave frequencies. Most communications satellites use geosynchronous orbits or near-geostationary orbits, although some new systems use low Earth-orbiting satellites.

· Earth notice satellites are satellites specifically designed to scrutinize Earth from orbit, similar to reconnaissance satellites but intended for non-military uses such as environmental monitoring, meteorology, map making etc. (See especially Earth Observing System.)

· Navigation satellites are satellites which use radio time signals transmitted to enable mobile receivers on the ground to determine their exact location. The relatively clear line of sight in the middle of the satellites and receivers on the ground, combined with ever-improving electronics, allows satellite pilotage systems to portion location to accuracies on the order of a few metres in real time.

· Reconnaissance satellites are Earth notice satellite or communications satellite deployed for military or intelligence applications. Little is known about the full power of these satellites, as governments who control them ordinarily keep facts pertaining to their reconnaissance satellites classified.

· Solar power satellites are proposed satellites built in high Earth orbit that use microwave power transmission to beam solar power to very large antenna on Earth where it can be used in place of accepted power sources.

· Space stations are man-made structures that are designed for human beings to live on in outer space. A space station is grand from other manned spacecraft by its lack of major propulsion or landing facilities -- instead, other vehicles are used as vehicle to and from the station. Space stations are designed for medium-term living in orbit, for periods of weeks, months, or even years.

· Weather satellites are satellites that primarily are used to monitor the weather and/or atmosphere of the Earth.

· Miniaturized satellites are satellites of unusually low weights and small sizes. New classifications are used to categorize these satellites: minisatellite (500-200 kg), microsatellite (below 200 kg), nanosatellite (below 10 kg).

Orbit types

Many times satellites are characterized by their orbit. Although a satellite may orbit at roughly any height, satellites are ordinarily categorized by their altitude:

· Low Earth Orbit (Leo: 200 - 1200km above the Earth's surface)

· Medium Earth Orbit (Ico or Meo: 1200 - 35286 km)

· Geosynchronous Orbit (Geo: 35786 km above Earth's surface) and Geostationary Orbit ( zero inclination geosynchronous orbit). These orbits are of singular interest for communication satellites and will be discussed in information later.

· High Earth Orbit (Heo: above 35786 km)

The following orbits are special orbits that are also used to categorize satellites:

· Molniya orbits: Is a class of a highly elliptic orbit. A satellite placed in this orbit spends most of its time over a designated area of the earth, a phenomenon known as apogee dwell. Molniya orbits are named after a series of Soviet/Russian Molniya communications satellites that have been using this class of orbits since the mid 1960s.

· Heliosynchronous or sun-synchronous orbit: A heliosynchronous orbit, or more ordinarily a sun-synchronous orbit is an orbit in which an object all the time passes over any given point of the Earth's surface at the same local solar time. This is a useful characteristic for satellites that image the earth's surface in visible or infrared wavelengths (e.g. weather, spy and remote sensing satellites).

· Polar orbit : A satellite in a polar orbit passes above or nearly above both poles of the planet (or other celestial body) on each revolution.

· Hohmann change orbit: For this singular orbit type, it is more base to recognize the satellite as a spacecraft. In astronautics and aerospace engineering, the Hohmann change orbit is an orbital maneuver that moves a spacecraft from one orbit to another.

· Supersynchronous orbit or drift orbit : orbit above Geo. Satellites will drift in a westerly direction.

· Subsynchronous orbit or drift orbit: orbits close to but below Geo. Used for satellites undergoing station changes in an eastern direction.

Communication Satellites

A communications satellite (sometimes abbreviated to comsat) is an artificial satellite stationed in space for the purposes of telecommunications. Contemporary communications satellites use geosynchronous orbits, Molniya orbits or low Earth orbits.

For fixed services, communications satellites provide a technology complementary to that of fiber optic submarine communication cables. For mobile applications, such as communications to ships and planes satellite based communicationis only the viable means of communications as application of other technologies, such as cable, are impractical or impossible.

Early missions: The origin of satellite communication can be traced to an report written by Arthur C. Clarke in 1945. He suggested that a radio relay satellite in an equatorial orbit with a period of 24 hours would remain stationary with respect to earth's surface and can be used for long-range radio communication, as it will over come the limitations imposed by earth curvature. Sputnik 1, The world's first artificial (non communication) satellite, was launched on October 4, 1957. The first satellite to relay communications was project Score in 1958, which used a tape recorder to store and forward voice messages. It was used to send a Christmas greeting to the world from President Eisenhower. Nasa launched an Echo satellite in 1960. This 100-foot aluminized Mylar balloon served as a passive reflector for radio communications. Courier 1B, (built by Philco) also was launched in 1960, was the world's first active repeater satellite. Given below are the details of milestones in satellite communcation history: -

· Herman Potocnik - describes a space station in geosynchronous orbit - 1928

· Arthur C. Clarke - proposes a station in geosynchronous orbit to relay communications and broadcast television - 1945

· Project Score - first communications satellite - 1958

· Echo I - first passive reflector satellite - August 1960

· Courier 1B - first active repeater satellite - October 1960

· Telstar - the first active direct relay satellite designed to forward television and high-speed data communications. Telstar was placed in an elliptical orbit (completed once every 2 hours and 37 minutes), rotating at a 45° angle above the equator. July 1962

· Syncom - first communications satellite in geosynchronous orbit. Syncom 2 revolved around the earth once per day at constant speed, but because it still had north-south appeal special equipment was needed to track it. 1963

· Oscar-Iii - first amateur radio communications satellite - March 1965

· Molniya - first Soviet communication satellite, highly elliptic orbit - October 1965

· Early Bird - Intelsat's first satellite for market aid - April 1965

· Orbita - first national Tv network based on satellite television - November 1967

· Anik 1 - the first national satellite television system, Canada, - 1973

· Westar 1, the Usa's first geosynchronous communications satellite - April 1974

· Ekran - first serial Direct-To-Home Tv communication satellite 1976

· Palapa A1 - first Indonesia communications satellite - July 8 1976

· Tdrss - first satellite designed to provide communications relay services for other spacecraft. - 1983

· Mars Global Surveyor - first communications satellite in orbit around someone else planet (Mars) - 1997

· Cassini spacecraft relays to Earth images from the Huygens probe as it lands on Saturn's moon, Titan, the longest relay to date. -- January 14, 2005

Depending on the need the communication satellites can be placed in assorted types of orbits. We discuss few base types: -

(a) Geostationary orbits Satellites: A satellite in a geostationary orbit appears to be in a fixed position to an earth-based observer. A geostationary satellite revolves around the earth at a constant speed once per day over the equator. The geostationary orbit is useful for communications applications because ground based antennae, which must be directed toward the satellite, can control effectively without the need for expensive equipment to track the satellite's motion. Especially for applications that need a large estimate of ground antennae (such as direct Tv distribution), the savings in ground equipment can more than elaborate the extra cost and onboard complexity of lifting a satellite into the relatively high geostationary orbit.

The plan of the geostationary communications satellite was first proposed by Arthur C. Clarke, building on work by Konstantin Tsiolkovsky and on the 1929 work by Herman Potočnik (writing as Herman Noordung) Das qoute der Befahrung des Weltraums - der Raketen-motor. In October 1945 Clarke published an report titled "Extra-terrestrial Relays" in the British magazine Wireless World. The report described the fundamentals behind the deployment of artificial satellites in geostationary orbits for the purpose of relaying radio signals. Thus Arthur C. Clarke is often quoted as being the creator of the communications satellite.

The first geostationary communications satellite was Anik 1, a Canadian satellite launched in 1972. The United States launched their own geostationary communication satellites afterward, with Western Union launching their Westar 1 satellite in 1974, and Rca Americom (later Ge Americom, now Ses Americom) launching Satcom 1 in 1975.
It was Satcom 1 that was instrumental in helping early cable Tv channels such as Wtbs (now Tbs Superstation), Hbo, Cbn (now Abc Family), and The Weather Channel come to be successful, because these channels distributed their programming to all of the local cable Tv headends using the satellite. Additionally, it was the first satellite used by broadcast Tv networks in the United States, like Abc, Nbc, and Cbs, to distribute their programming to all of their local affiliate stations. The hypothesize that Satcom 1 was so widely used is that it had twice the communications capacity of Westar 1 (24 transponders as opposed to Westar 1's 12), which resulted in lower transponder usage costs.

By 2000 Hughes Space and Communications (now Boeing Satellite Systems) had built nearly 40 percent of the satellites in aid worldwide. Other major satellite manufacturers consist of Space Systems/Loral, Lockheed Martin (owns former Rca Astro Electronics/Ge Astro Space business), Northrop Grumman, Alcatel Space and Eads Astrium.

(b) Low-Earth-orbiting satellites: A low Earth orbit typically is a circular orbit about 150 kilometers above the earth's surface and, correspondingly, a period (time to revolve around the earth) of about 90 minutes. Because of their low altitude, these satellites are only visible from within a radius of roughly 1000 kilometers from the sub-satellite point. In addition, satellites in low earth orbit change their position relative to the ground position quickly. So even for local applications, a large estimate of satellites are needed if the mission requires uninterrupted connectivity.

Low earth orbiting satellites are less expensive to position in space than geostationary satellites and, because of their closer presence to the ground, need lower signal strength. So there is a trade off in the middle of the estimate of satellites and their cost. In addition, there are important differences in the onboard and ground equipment needed to support the two types of missions.

A group of satellites working in concert thus is known as a satellite constellation. Two such constellations which were intended for provision for hand held telephony, primarily to remote areas, were the Iridium and Globalstar. The Iridium law has 66 satellites. someone else Leo satellite constellation, with backing from Microsoft entrepreneur Paul Allen, was to have as many as 720 satellites. It is also possible to offer discontinuous coverage using a low Earth orbit satellite capable of storing data received while passing over one part of Earth and transmitting it later while passing over someone else part. This will be the case with the Cascade law of Canada's Cassiope communications satellite.

(c) Molniya satellites: As mentioned, geostationary satellites are constrained to control above the equator. As a consequence, they are not all the time convenient for providing services at high latitudes: for at high latitudes a geostationary satellite may appear low on (or even below) the horizon, affecting connectivity and causing multipathing (interference caused by signals reflecting off the ground into the ground antenna). The first satellite of Molniya series was launched on April 23, 1965 and was used for experimental transmission of Tv signal from Moscow uplink station to downlink stations, placed in Russian Far East, in Khabarovsk, Magadan and Vladivostok. In November of 1967 Soviet engineers created a unique law of national Tv network of satellite television, called Orbita that was based on Molniya satellites.

Molniya orbits can be an sharp alternative in such cases. The Molniya orbit is highly inclined, guaranteeing good elevation over prime positions during the northern portion of the orbit. (Elevation is the extent of the satellite's position above the horizon. Thus a satellite at the horizon has zero elevation and a satellite directly overhead has elevation of 90 degrees). Furthermore, the Molniya orbit is so designed that the satellite spends the great majority of its time over the far northern latitudes, during which its ground footprint moves only slightly. Its period is one half day, so that the satellite is available for doing over the targeted region for eight hours every second revolution. In this way a constellation of three Molniya satellites (plus in-orbit spares) can provide uninterrupted coverage.

Molniya satellites are typically used for telephony and Tv services over Russia. someone else application is to use them for mobile radio systems (even at lower latitudes) since cars traveling through urban areas need way to satellites at high elevation in order to fetch good connectivity, e.g. In the presence of tall buildings.

Applications of Satellites

(a) Telephony: One of the major applications of a communication satellite is in provision of long length telephone services. The connectivity is through frequency division complicated way (Fdma) or time division complicated access(Tdma) predominantly. Telephone subscribers can be connected through a network of exchanges which are in turn connected to satellite earth stations which uplink the traffic to satellite for supplementary processing.

(b) Television and Radio: There are two types of satellites used for television and radio:

(i) Direct Broadcast Satellite (Dbs): A direct broadcast satellite is a communications satellite that transmits to small Dbs satellite dishes (usually 18" to 24" in diameter). Direct broadcast satellites ordinarily control in the upper portion of the Ku band. Dbs technology is used for Dth-oriented (Direct-To-Home) satellite Tv services, such as DirecTv and Dish Network in the United States, ExpressVu in Canada, and Sky Digital in the Uk.

(ii) Fixed aid Satellite (Fss): Use the C band, and the lower portions of the Ku bands. They are ordinarily used for broadcast feeds to and from television networks and local affiliate stations (such as program feeds for network and syndicated programming, live shots, and backhauls), as well as being used for length studying by schools & universities, enterprise television (Btv), videoconferencing, and general market telecommunications. Fss satellites are also used to distribute national cable channels to cable Tv headends. Fss satellites differ from Dbs satellites in that they have a lower Rf power production than the latter, requiring a much larger dish for reception (3 to 8 feet in diameter for Ku band, and 12 feet on up for C band). Fss satellite technology was also originally used for Dth satellite Tv from the late 1970s to the early 1990s in the Usa in the form of Tvro (TeleVision Receive Only) receivers and dishes (a.k.a. Big-dish, or more pejoratively known as big ugly dish, systems). It was also used in its Ku band form for the now-defunct Primestar satellite Tv service.

(c) mobile satellite technologies: Initially available for broadcast to stationary Tv receivers, by 2004 favorite mobile direct broadcast applications made their appearance with that advent of two satellite radio systems in the United States: Sirius and Xm Satellite Radio Holdings. Some manufacturers have also introduced special antennas for mobile reception of Dbs television. Using Gps technology as a reference, these antennas automatically re-aim to the satellite no matter where or how the vehicle (that the antenna is mounted on) is situated. These mobile satellite antennas are favorite with some recreational vehicle owners. Such mobile Dbs antennas are also used by JetBlue Airways for DirecTv (supplied by LiveTv, a subsidiary of JetBlue), which passengers can view on-board on Lcd screens mounted in the seats.

(d) Amateur radio: Amateur radio operators have way to the Oscar satellites that have been designed specifically to carry amateur radio traffic. Most such satellites control as space borne repeaters, and are ordinarily accessed by amateurs adequate with Uhf or Vhf radio equipment and highly directional antennas such as Yagis or dish antennas. Due to the limitations of ground-based amateur equipment, most amateur satellites are launched into fairly low Earth orbits, and are designed to deal with only a Little estimate of brief contacts at any given time. Some satellites also provide data-forwarding services using the X.25 or similar protocols.

Satellite Broadband Services: In new years, satellite communication technology has been used as a means to associate to the Internet via broadband data connections. This is can be very useful for users to test who are placed in very remote areas, and can't way a wireline broadband or dialup connection.

Countries with satellite start capability

This list includes counties with an independent quality to place satellites in orbit, along with production of the considerable start vehicle. Many more countries have built satellites that were launched with the aid of others. The French and British capabilities are now subsumed by the European Union under the European Space Agency.

First start by country

Country Year of first launch First satellite

Russia 1957 "Sputnik 1"

United States 1958 "Explorer 1"

France 1965 "Asterix"

Japan 1970 "Osumi"

China 1970 "Dong Fang Hong I"

United Kingdom 1971 "Prospero X-3"

European Union 1979 "Ariane 1"

India 1980 "Rohini"

Israel 1988 "Ofea 1"

Iran 2005 "Sina 1"

In 1998, North Korea claimed to have launched a satellite, but this was never confirmed, and widely believed to be a cover for the test start of the Taepodong-1 missile over Japan (See Kwangmyongsong).