By Ed Tittel
With the move to Digital TV, right around the corner, many are making a decision regarding upgrading their TV service. The question now is what. Satellite or Cable. We here at Digital Landing try and answer some common question for those ready to make the leap
Q: What is satellite TV service? How much does it cost?
Satellite TV service gets its TV signals from satellites in geosynchronous orbit. Because they stay in the same position relative to the earth's surface at all times, once a satellite antenna (usually, a dish of some kind) is properly aimed, it can be left as-is thereafter. Satellite signals are broadcast from a ground station to multiple satellites, which then broadcast those signals back to the earth across huge expanses of territory. Anybody with a satellite dish (the antenna), plus the proper signal processing gear (a set-top box of some kind, usually called a satellite receiver, is required for each TV set on which you want to watch the provider's programming) that can "see" a satellite can pick up the signal. A single antenna can feed multiple satellite receivers, but a physical cable is routed from the antenna to each receiver (inside the house, both cable and satellite TV require cables for each TV set).
Satellite providers control access to their networks by including special encryption and encoding in their signals, and tightly controlling the equipment that can read and play back those signals, to prevent unauthorized users from tuning in and obtaining free TV service.
Satellite TV service costs vary, primarily according to the channels that subscribers elect to pay for. That said, both DirecTV and Dish Network (the two primary satellite providers in North America) offer basic packages for $20 to $25 per month. Add-on options for HDTV, sports channels, movie channels, and so forth usually cost anywhere from $8 to $25 per month each (or come in season-long subscriptions for sports such as NFL football, NBA basketball and so forth). Lots of bundles are available in the $30 to $55 a month range, but it's easy to spend $100 a month or more on satellite TV services, especially if you like sports or movies, or both.
Dish Network offers equipment to subscribers at no charge, including DVR (digital video recording) or HDTV (high-definition television) receivers. DirecTV charges $99 for SDTV DVR receivers, and $299 for HDTV DVR receivers (check for rebates).
Q: What is cable TV service? How much does it cost?
Cable TV service basically entails running a physical broadband cable into your household, usually some kind of high-bandwidth coaxial cable (though some fiber-optic-based offerings are starting to become available in some markets). Cable TV companies operate various types of broadcast equipment that essentially combine hundreds of analog and digital TV channels into a single cable that can be decoded and interpreted when passed into the right kind of set-top box. Cable companies monitor the hardware attached to their networks very closely, and permit only devices with known physical hardware addresses to access their signals. Though you can buy your own cable equipment in some markets, you can't use that equipment until the provider reads its hardware address and enables it to work with their signals. As with satellite TV, a set-top box is generally required for each TV set on which you want to watch cable TV signals, and a physical cable hook-up for each such box is also required. Most cable providers also have to ensure that individual hook-ups are "digital ready" before they can accommodate digital set-top boxes and HDTV signals.
Basic cable TV costs are generally in the same league as basic satellite TV costs--again $20 to $25 a month--but cable TV providers are subject to local fees and taxes (satellite providers are not), and you must generally rent set-top boxes from cable providers for anywhere from $3 a month per device (more for those with digital, HDTV or DVR capabilities). In general, the cable company not only controls but also owns the equipment you use to watch their programming. So, basic cable generally costs anywhere from $5 to $10 a month more than satellite for similar service, plus $3 a month and up for each set-top box you have installed. You can omit the set-top boxes on the additional TVs, but you will probably not be able to receive all the cable channels you pay for on those sets.
Q: How do the costs for cable and satellite TV service compare?
Most experts generally rule the cost equation slightly in favor of satellite, even when you have to buy the equipment you use to receive (and sometimes, to record) TV, be it standard television or HDTV. That's because the costs of renting cable equipment generally exceed those for buying satellite equipment over time, and because the regular monthly fees and taxes that get tacked onto cable TV charges also add to the overall cost. That confers only a slight edge, however, and shouldn't be the only factor involved in your selection.
Q: How do costs of equipment purchase compare to rental costs?
When satellite providers offer equipment at no charge, they generally require at least a one-year subscription commitment or a contract of similar duration. When they charge for the equipment, it usually costs anywhere from $49 for a basic standard TV set-top box, to as much as $299 for a set-top box that can record HDTV signals.
Cable operators generally charge $3 per set-top box per month ($36 a year) for basic standard TV devices, and up to $10 a month ($120 per year) for set-top boxes that can record HDTV signals. If you stay with either provider longer than two or three years, the satellite service costs come out somewhat lower than the cable service costs because you'll typically pay off that equipment somewhere in the second or third year of ownership, as compared with cable TV costs. But such equipment generally needs to be replaced every five to seven years (if not more often for real equipment aficionados), so equipment costs do continue to factor into the overall burden for either type of service.
Q: What kinds of equipment are required for cable service? For satellite service?
For both services, each TV set on which you want to watch provider programming requires a set-top box of some kind, which may or may not include any or all of the following: analog TV signals (satellite is all-digital, so this applies only to cable), digital TV signals, HDTV signals, plus digital video recording for standard TV (less expensive, more hours of TV recording per device) and HDTV (more expensive, less hours of TV recording per device). Note that all HDTV programming is digital, and an increasing number of standard television channels are also digital; the FCC mandates that all U.S. TV broadcasts will be digital by February 9, 2009.
Q: What are the primary differences between cable and satellite TV services?
That's tough to say, because the hundreds of cable TV providers that exist all have somewhat different offerings, and because even the offerings from the two primary satellite providers also differ substantially. Conventional wisdom is that satellite TV offers more and better for-a-fee sports and entertainment packages, and a broader selection of HDTV channels, while cable TV offers more and better local stations (they will often rebroadcast all of the OTA channels in a viewing area on cable, and usually operate one or more stations of their own including news, weather, and public access programming).
Look closely at the stations included in their packages, and weigh the importance of the availability of local channels when choosing between the two offerings.
Q: How many channels are typical for cable offerings? For satellite offerings?
Basic satellite offerings typically include 40 to 50 channels, and premium offerings usually include 140 to as many as 250 channels. Cable offerings typically include at least 20 basic channels, and another 50-60 standard channels, with as many as 200-300 more channels available in family, lifestyle, news and entertainment bundles, plus additional channels for HDTV, movies, sports and more.
Q: What offerings differentiate cable and satellite services? What kinds of advantages result on each side?
Satellite usually takes the edge when it comes to entertainment (movies, live concert simulcasts, and special programming) and sports (especially for "season pass" offerings for all games in sports such as football, basketball, hockey and NASCAR). Cable takes the edge in on-demand programming because the providers' equipment infrastructure makes it easy to deliver rebroadcast of free and for-a-fee programming on demand, and to deliver pay-per-view services for movies and other premium programming.
Q: What kinds of bundled services are available from cable providers? Satellite providers? Who else gets involved?
When it comes to channel lineups, both satellite and cable providers apparently compete on the same playing field. Both offer all kinds of family channels, lifestyle channels, sport channels, news channels, movie channels and HDTV packages. Generally, cable takes the edge on local channel offerings and on-demand services, and satellite takes the edge on sports and movie packages, as well as for high-ticket pay-per-view and entertainment offerings.
These days, both cable and satellite providers offer bundles of a different kind as well. Cable companies invented the so-called "triple play" terminology, wherein they deliver television, telephone and Internet access to households on a single bill, usually at a discount from individual items on this list. Satellite companies will gladly provide the same combinations to their customers, though they must usually partner up with communications carriers for Internet and telephone services. You can get a true "triple play" from cable companies such as Time Warner or Cox, for example. If you turn to Dish Network or DirecTV for triple play, a company such as AT&T or Sprint/Nextel is also likely to be involved in delivering those services to you.
Q: Do satellite or cable providers require service contracts or commitments?
Sometimes. Satellite companies require commitments, and cable companies sometimes do. If you are simply signing up for cable TV, you most likely will not need to sign a contract. But if you bundle another service into the deal, such as phone or Internet hookup, then the company will likely have you sign a contract.However, even for satellite where a commitment is required, you can often talk your way out of contractual commitments if you can make a substantial case that you're not getting the services you paid for, or you have legitimate reasons to be profoundly dissatisfied with those services.
Q: What happens to the provider equipment when you cancel your service?
Generally, you will be held responsible for the safe return of equipment in situations where the provider has furnished you with set-top boxes, remote controls, and so forth that it owns and you do not. That usually means you must return the equipment to them yourself, or pay for a service call to have their field service personnel come and pick the equipment up at your house. Otherwise, you will receive a bill from the provider for that equipment, and it generally includes enough zeroes to command serious attention and swift action (Author's note: I moved recently and had to return the equipment from the old house, although I stayed with the same provider. Thirty days after the move, a bill for $700 for a digital and an analog set-top box and remotes showed up, and spurred immediate action to avoid potential credit problems that might have otherwise resulted).
Q: How does service availability differ for cable and satellite? What effects does this have on my TV signal?
The biggest difference between cable and satellite is availability. Cable is available only in neighborhoods where the provider can run a cable into your home. Satellite is available anywhere you can put an antenna that can "see" one of the satellite provider's satellites in orbit (this does require a line of sight to that satellite). In most metro areas, cable is a viable option and worth comparing to satellite. In most rural areas, satellite is the only option, because cable isn't available.
Whether you set up your satellite dish in an urban, suburban or rural setting, a clear line of site to the satellite from the dish is an absolute must. In some cases, trees or other buildings may partially obscure that line of sight, and will have a negative effect on signal quality. That can be particularly vexing when the weather gets bad, and high winds move trees into the line of sight when they're not ordinarily a problem. Be sure to get the dish situated with the clearest possible line of sight to the satellite, to minimize the effects of weather or obstructions, occasional or otherwise.
Q: How do high-definition TV (HDTV) offerings from satellite and cable providers compare? Who's got the edge?
For both types of providers, you must usually obtain HD-capable set-top boxes to permit you to view HDTV signals in the first place. This will usually add to your recurring monthly equipment costs (cable or satellite) or equivalent purchase costs (satellite). Then, you must sign up for one or more HDTV packages so you will have some HD programming to watch. From both types of providers, you can sign up for various types of HD programming (basic HDTV package, HD movies, HD sports, on-demand or pay-per-view HD programming). Generally, most cable stations top out on HD channels somewhere between 80 and 120 stations; both major satellite providers offer 140 HD stations or more. Note that these stations are split among various channel packages, so there will be extra fees to obtain most or all of them). Therefore, satellite has the HD edge right now.
Q: How does installation compare for cable versus satellite?
When it comes to cable, installation generally comes as part of initial account set-up. The cable company generally sends an installer out to make sure the cable is hooked up and working properly at all outlets when you establish your account. Generally, there is no extra charge for that service. You can return to a local cable provider office to swap out equipment after the initial set-up.
Satellite can be a different matter. Though most account set-ups have an option for professional installation, charges can be associated with that service. Still, it is strongly recommended to have antennas, cables and set-top boxes professionally installed, charges or not. Sometimes, satellite providers waive installation fees as part of promotional campaigns, or in return for longer-term account commitments. Check the terms and conditions carefully, and ask about installation and set-up as part of your overall background research before making any account commitments. If anything, installation is even more important for satellite than for cable; proper antenna positioning and aiming is key to obtaining the best possible signal.
Q: How do service and support compare for satellite vs. cable? Which of the two experiences more outages?
According to JD Power and Associates, satellite customers consistently rank both major satellite providers as among the best of all companies when it comes to service and support. Cable providers fare worse, typically receiving grades in the fair to poor range from the majority of customers. Also, cable operators report outage rates of 3 percent nationwide, while satellite providers report outage rates of less than 1 percent. Most experts agree that satellite beats cable when it comes to customer support and service and in terms of overall uptime and availability.
Q: Does digital TV matter more for cable or satellite service?
Because satellite TV is all digital, and cable can deliver both digital and analog TV across its broadband infrastructure, you might say that digital TV matters more for satellite. Also, FCC requirements that all broadcast signals be digital by February 9, 2009, don't apply to cable because cable signals aren't broadcast over the air in a conventional sense. Most cable companies are converting aggressively anyway because of the higher quality and easier manageability of digital as opposed to analog technologies. Because HD is digital by definition and most of the growth and innovation is occurring in this area, the marketplace is driving cable companies to be as capable and competitive in digital programming as the satellite companies.
Q: How does local channel access compare for satellite versus cable?
Normally, cable companies make arrangements with all local broadcast television stations to carry their signals on cable wherever they offer cable services to their customers. Local access on satellite varies to a great extent, so that you can expect access to local channels in most metropolitan areas, but station availability in rural areas will depend on what stations are active in the broadcast area, and whether or not the satellite company has made arrangements to pick up and include the signal feed from those stations in the satellite feed available through your antenna. Often, local channel access will be same for both systems; in some cases, cable may carry more or all of the local channels, whereas satellite may carry only a few or some of those same channels.
Q: What does it cost to add sets for cable TV service? For satellite TV service?
Most cable TV service offerings add an additional charge for each set-top box you use, and additional costs apply for digital signals (including for HDTV channels) and for DVR capability. Costs start at $3 a month or so for set-top boxes, and go up as you add features and digital support. Most satellite TV service offerings include up to four hook-ups in the basic service cost. Often, that's because you must purchase your own set-top boxes and/or DVRs (see question #2).
Q: What if I want to use a digital video recorder with cable service? With satellite service?
Generally, you can either rent a DVR from your cable provider or purchase a standard or HDTV DVR from a third-party company such as TiVo. Purchasing can be expensive: Standard TV TiVo models start at approximately $300 and HDTV models at roughly $800 and also come with monthly service commitments.
With satellite service, you can often buy your own DVR right from the provider instead of going to a third party. Third-party offerings such as TiVo are also available at the same prices as their cable counterparts. Given the relatively high cost of such equipment, it's often less costly to rent rather than buy in this case.
Q: Overall, which type of service has the edge: cable or satellite?
Because of more and better HDTV offerings, more sports and interesting entertainment offerings, and a better record for service and support, most experts give an edge to satellite over cable. But for those to whom "triple-play" packages (TV, phone, and rel=nofollow [http://www.digitallanding.com]Internet service) are appealing, or for whom access to local channels or on-demand services is important, cable pulls ahead of satellite. Both will certainly do the job, and neither has an absolute edge over the other.
You deserve to get the most out of your services, whether it's high-speed Internet, phone, cable, or HDTV. Digital Landing is here to help, making it easy to find out everything you need to know about digital services for your home.
Article Source: [http://EzineArticles.com/?Making-the-Choice---Satellite-Or-Cable-TV?&id=1703811] Making the Choice - Satellite Or Cable TV?
Friday, June 4, 2010
Introduction and Brief History of Satellites and Communication Satellites
By Anil Nigam
Introduction and Brief History of Satellites
A satellite is any object that orbits another object (which is known as its primary). All masses that are part of the solar system, including the Earth, are satellites either of the Sun, or satellites of those objects, such as the Moon. It is not always a simple matter to decide which is the 'satellite' in a pair of bodies. Because all objects exert gravity, the motion of the primary object is also affected by the satellite. If two objects are ufficiently similar in mass, they are generally referred to as a binary system rather than a primary 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 primary object. In popular usage, the term 'satellite' normally refers to an artificial satellite (a man-made object that orbits the Earth or another body).
In May, 1946, the Preliminary Design of an Experimental World-Circling Spaceship stated, "A satellite vehicle with appropriate instrumentation can be expected 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 research was conducted using V-2s and Aerobee rockets. This allowed measurements of atmospheric pressure, density, and temperature 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 eventually released the above report, but did not believe that the satellite was a potential military weapon; rather they considered 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 involved using a Jupiter C rocket to launch a small satellite called Explorer 1 on January 31, 1958.
On July 29, 1955, the White House announced that the U.S. intended to launch satellites by the spring of 1958. This became known as Project Vanguard. On July 31, the Soviets announced that they intended to launch a satellite by the fall of 1957 and on October 4, 1957 Sputnik I was launched into orbit, which triggered the Space Race between 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 observation 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 recent systems use low Earth-orbiting satellites.
· Earth observation satellites are satellites specifically designed to observe 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 between the satellites and receivers on the ground, combined with ever-improving electronics, allows satellite navigation systems to measure location to accuracies on the order of a few metres in real time.
· Reconnaissance satellites are Earth observation satellite or communications satellite deployed for military or intelligence applications. Little is known about the full power of these satellites, as governments who operate them usually keep information 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 conventional power sources.
· Space stations are man-made structures that are designed for human beings to live on in outer space. A space station is distinguished from other manned spacecraft by its lack of major propulsion or landing facilities -- instead, other vehicles are used as transport 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 climate 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 almost any height, satellites are commonly 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 particular interest for communication satellites and will be discussed in detail 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 commonly a sun-synchronous orbit is an orbit in which an object always 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 transfer orbit: For this particular orbit type, it is more common to identify the satellite as a spacecraft. In astronautics and aerospace engineering, the Hohmann transfer 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. Modern 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 article 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 transmit 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 motion 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 commercial service - 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 another 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 various types of orbits. We discuss few common 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 operate effectively without the need for expensive equipment to track the satellite's motion. Especially for applications that require a large number of ground antennae (such as direct TV distribution), the savings in ground equipment can more than justify the extra cost and onboard complexity of lifting a satellite into the relatively high geostationary orbit.
The concept 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 Problem der Befahrung des Weltraums - der Raketen-motor. In October 1945 Clarke published an article titled "Extra-terrestrial Relays" in the British magazine Wireless World. The article 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 inventor 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 become 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 reason 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 service worldwide. Other major satellite manufacturers include 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 number 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 proximity to the ground, require lower signal strength. So there is a trade off between the number 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 system has 66 satellites. Another 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 another part. This will be the case with the CASCADE system of Canada's CASSIOPE communications satellite.
(c) Molniya satellites: As mentioned, geostationary satellites are constrained to operate above the equator. As a consequence, they are not always suitable 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, located in Russian Far East, in Khabarovsk, Magadan and Vladivostok. In November of 1967 Soviet engineers created a unique system of national TV network of satellite television, called Orbita that was based on Molniya satellites.
Molniya orbits can be an appealing alternative in such cases. The Molniya orbit is highly inclined, guaranteeing good elevation over selected 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 operation 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. Another application is to use them for mobile radio systems (even at lower latitudes) since cars traveling through urban areas need access to satellites at high elevation in order to secure 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 distance telephone services. The connectivity is through frequency division multiple access (FDMA) or time division multiple 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 further 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 generally operate 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 Service Satellite (FSS): Use the C band, and the lower portions of the Ku bands. They are normally 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 distance learning by schools & universities, business television (BTV), videoconferencing, and general commercial 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 output 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 popular mobile direct broadcast applications made their appearance with that arrival 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 popular 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 access to the OSCAR satellites that have been designed specifically to carry amateur radio traffic. Most such satellites operate as space borne repeaters, and are generally accessed by amateurs equipped 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 limited number 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 recent years, satellite communication technology has been used as a means to connect to the Internet via broadband data connections. This is can be very useful for users to test who are located in very remote areas, and can't access a wireline broadband or dialup connection.
Countries with satellite launch capability
This list includes counties with an independent capability to place satellites in orbit, including production of the necessary launch 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 launch 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 launch of the Taepodong-1 missile over Japan (See Kwangmyongsong).
Author has 28 years of experience in the field of Teaching and Management. He is M. Tech from IIT Kanpur and has worked in different capacities including Signal corps Indian Army, Regional Manager for a Telecom Company. Currently he is Associate Professor with ITM, Gurgaon that is rated as best Engineering colleges of North India.
Article Source: [http://EzineArticles.com/?Introduction-and-Brief-History-of-Satellites-and-Communication-Satellites&id=130348] Introduction and Brief History of Satellites and Communication Satellites
Introduction and Brief History of Satellites
A satellite is any object that orbits another object (which is known as its primary). All masses that are part of the solar system, including the Earth, are satellites either of the Sun, or satellites of those objects, such as the Moon. It is not always a simple matter to decide which is the 'satellite' in a pair of bodies. Because all objects exert gravity, the motion of the primary object is also affected by the satellite. If two objects are ufficiently similar in mass, they are generally referred to as a binary system rather than a primary 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 primary object. In popular usage, the term 'satellite' normally refers to an artificial satellite (a man-made object that orbits the Earth or another body).
In May, 1946, the Preliminary Design of an Experimental World-Circling Spaceship stated, "A satellite vehicle with appropriate instrumentation can be expected 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 research was conducted using V-2s and Aerobee rockets. This allowed measurements of atmospheric pressure, density, and temperature 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 eventually released the above report, but did not believe that the satellite was a potential military weapon; rather they considered 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 involved using a Jupiter C rocket to launch a small satellite called Explorer 1 on January 31, 1958.
On July 29, 1955, the White House announced that the U.S. intended to launch satellites by the spring of 1958. This became known as Project Vanguard. On July 31, the Soviets announced that they intended to launch a satellite by the fall of 1957 and on October 4, 1957 Sputnik I was launched into orbit, which triggered the Space Race between 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 observation 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 recent systems use low Earth-orbiting satellites.
· Earth observation satellites are satellites specifically designed to observe 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 between the satellites and receivers on the ground, combined with ever-improving electronics, allows satellite navigation systems to measure location to accuracies on the order of a few metres in real time.
· Reconnaissance satellites are Earth observation satellite or communications satellite deployed for military or intelligence applications. Little is known about the full power of these satellites, as governments who operate them usually keep information 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 conventional power sources.
· Space stations are man-made structures that are designed for human beings to live on in outer space. A space station is distinguished from other manned spacecraft by its lack of major propulsion or landing facilities -- instead, other vehicles are used as transport 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 climate 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 almost any height, satellites are commonly 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 particular interest for communication satellites and will be discussed in detail 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 commonly a sun-synchronous orbit is an orbit in which an object always 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 transfer orbit: For this particular orbit type, it is more common to identify the satellite as a spacecraft. In astronautics and aerospace engineering, the Hohmann transfer 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. Modern 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 article 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 transmit 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 motion 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 commercial service - 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 another 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 various types of orbits. We discuss few common 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 operate effectively without the need for expensive equipment to track the satellite's motion. Especially for applications that require a large number of ground antennae (such as direct TV distribution), the savings in ground equipment can more than justify the extra cost and onboard complexity of lifting a satellite into the relatively high geostationary orbit.
The concept 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 Problem der Befahrung des Weltraums - der Raketen-motor. In October 1945 Clarke published an article titled "Extra-terrestrial Relays" in the British magazine Wireless World. The article 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 inventor 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 become 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 reason 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 service worldwide. Other major satellite manufacturers include 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 number 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 proximity to the ground, require lower signal strength. So there is a trade off between the number 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 system has 66 satellites. Another 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 another part. This will be the case with the CASCADE system of Canada's CASSIOPE communications satellite.
(c) Molniya satellites: As mentioned, geostationary satellites are constrained to operate above the equator. As a consequence, they are not always suitable 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, located in Russian Far East, in Khabarovsk, Magadan and Vladivostok. In November of 1967 Soviet engineers created a unique system of national TV network of satellite television, called Orbita that was based on Molniya satellites.
Molniya orbits can be an appealing alternative in such cases. The Molniya orbit is highly inclined, guaranteeing good elevation over selected 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 operation 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. Another application is to use them for mobile radio systems (even at lower latitudes) since cars traveling through urban areas need access to satellites at high elevation in order to secure 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 distance telephone services. The connectivity is through frequency division multiple access (FDMA) or time division multiple 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 further 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 generally operate 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 Service Satellite (FSS): Use the C band, and the lower portions of the Ku bands. They are normally 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 distance learning by schools & universities, business television (BTV), videoconferencing, and general commercial 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 output 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 popular mobile direct broadcast applications made their appearance with that arrival 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 popular 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 access to the OSCAR satellites that have been designed specifically to carry amateur radio traffic. Most such satellites operate as space borne repeaters, and are generally accessed by amateurs equipped 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 limited number 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 recent years, satellite communication technology has been used as a means to connect to the Internet via broadband data connections. This is can be very useful for users to test who are located in very remote areas, and can't access a wireline broadband or dialup connection.
Countries with satellite launch capability
This list includes counties with an independent capability to place satellites in orbit, including production of the necessary launch 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 launch 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 launch of the Taepodong-1 missile over Japan (See Kwangmyongsong).
Author has 28 years of experience in the field of Teaching and Management. He is M. Tech from IIT Kanpur and has worked in different capacities including Signal corps Indian Army, Regional Manager for a Telecom Company. Currently he is Associate Professor with ITM, Gurgaon that is rated as best Engineering colleges of North India.
Article Source: [http://EzineArticles.com/?Introduction-and-Brief-History-of-Satellites-and-Communication-Satellites&id=130348] Introduction and Brief History of Satellites and Communication Satellites
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