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Why are ground stations in continuous contact with satellites in geostationary orbit?
Wiki User
∙ 12y ago
Just imagine managing a system of communication satellites which were non-geostationary. Data needs to be sent to one city, one home, but the satellite for the job is different every time. The task would be manageable, but unnecessarily difficult.
Further more, metropolises must have priority over small towns- or oceans. New York needs more satellites than Apple Creek Ohio or the Atlantic Ocean.
Finally, many satellites serve a very specific audience. Your favorite radio station would almost never come into reception if the satellite broadcasting it is circling the world.
Wiki User
∙ 14y ago
Wiki User
∙ 12y agoSince the satellite appears fixed in the sky, antennas can also stay in a fixed
position to communicate with it, and don't need to be continuously guided.
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How many GPS satellites are there and when were they put in orbit?
GPS SatellitesThere are 30 GPS satellites -- called NAVSTARs -- in place and the oldest one was launched in 1989. These are just the ones in operation now -- another 22 have been launched since the program started in 1978, but are no longer working. The design of the satellites has remained essentially the same over the years; the differences have just been in their operations.The first 11 satellites, known as Group I and designed by Rockwell International, were launched into orbit between 1978 and 1985 from Vandenburg Air Force Base in California. Each of these satellites contained one Cesium and two Rubidium atomic clocks and could provide navigation and standard positioning information. Continuous contact with the Ground Control Segment (CS) was required for their operation. They were designed to last five years, but most lasted much longer.The next group of 9 satellites are called Group II and were also designed by Rockwell. These were the first to provide precision positioning information for military use and to be able to operate for 14 days without contact with the CS. Group II satellites contained four clocks two Cesium and two Rubidium and were launched between February 1989 and October 1990 from Cape Canaveral Air Force Station in Florida. They were designed to last 7.3 years and two currently remain in operation.The Group IIA satellites were next group to be designed by Rockwell and numbered 19. They are similar to the Group II satellites, except they have the ability to operate 180 days without contact with CS. These were launched from Cape Canaveral between November 1990 and November 1997. All but three of these satellites are still in operation.The most recent type, Group IIR, were designed by Lockheed Martin and each have three Rubidium clocks. They were designed to provide more accurate information through a combination of ranging techniques and communication between the satellites. They are also designed to last slightly longer (7.8 years) and to have improved independent controls. There are currently 12 such satellites in orbit the most recent launched in November 2004.The satellites are launched via a Delta II rocket designed by Boeing. These are expendable launch vehicles (ELVs), meaning they are intended for one use only. Each of these ELVs consists of the following:Stage I which contains fuel and oxygen tanks to supply the main engine during its climb;Solid rocket booster motors to provide additional thrust during the first two minutes of flight;Stage II which contains the fuel and oxidizer tanks that supply the engine needed to insert the ELV into orbit and the brains of the ELV, including its guidance system;Stage III that has a solid rocket motor to provide any needed velocity change.More input from others:According to SMC Fact Sheet (URLhttp://www.losangeles.af.mil/smc/pa/fact_sheets/gps_fs.htm), as well as Garmin (URL http://www.garmin.com/aboutGPS/), there are 24 satellites in the system with an additional 4 on reserve.
What are uses of artificial satellite?
artificial satellite object constructed by humans and placed in orbit around the earth or other celestial body (see also space probe). The satellite is lifted from the earth's surface by arocket and, once placed in orbit, maintains its motion without further rocket propulsion. The first artificial satellite, Sputnik I,was launched on Oct. 4, 1957, by the USSR; a test payload of a radio beacon and a thermometer demonstrated the feasibility of orbiting a satellite. The first U.S. satellite,Explorer I,launched on Jan. 31, 1958, returned data that was instrumental in the discovery of the Van Allen radiation belts. During the first decade of space exploration, all of the satellites were launched from either the United States or USSR. Today, there are more than three dozen launch sites in use or under construction in more than a dozen countries.Satellite OrbitsIf placed in an orbit high enough to escape the frictional effects of the earth's atmosphere, the motion of the satellite is controlled by the same laws of celestial mechanics that govern the motions of natural satellites, and it will remain in orbit indefinitely. At heights less than 200 mi (320 km) the drag produced by the atmosphere will slow the satellite down, causing it to descend into the denser portion of the atmosphere where it will burn up like a meteor. To attain orbital altitude and velocity, multistage rockets are used, with each stage falling away as its fuel is exhausted; the effect of reducing the total mass of the rocket while maintaining its thrust is to increase its speed, thus allowing it to achieve the required velocity of 5 mi per sec (8 km per sec). At this speed the rocket's forward momentum exactly balances its downward gravitational acceleration, resulting in orbit. Once above the lower atmosphere, the rocket bends to a nearly horizontal flight path, until it reaches the orbital height desired for the satellite.Unless corrections are made, orbits are usually elliptical; perigee is the point on the orbit closest to the earth, and apogee is the point farthest from the earth. Besides this eccentricity an orbit of a satellite about the earth is characterized by its plane with respect to the earth. An equatorial orbit lies in the plane of the earth's orbit. A polar orbit lies in the plane passing through both the north and south poles. A satellite's period (the time to complete one revolution around the earth) is determined by its height above the earth; the higher the satellite, the longer the period. At a height of 200 mi (320 km), the period of a circular orbit is 90 min; at 500 mi (800 km), it increases to 100 min. At a height of 22,300 mi (36,000 km), a satellite has a period of exactly 24 hr, the time it takes the earth to rotate once on its axis; such an orbit is called geosynchronous. If the orbit is also equatorial, the satellite will remain stationary over one point on the earth's surface.Tracking and TelemetrySince more than 1,000 satellites are presently in orbit, identifying and maintaining contact requires precise tracking methods. Optical and radar tracking are most valuable during the launch; radio tracking is used once the satellite has achieved a stable orbit. Optical tracking uses special cameras to follow satellites illuminated either by the sun or laser beams. Radar tracking directs a pulse of microwaves at the satellite, and the reflected echo identifies both its direction and distance. Nearly all satellites carry radio transmitters that broadcast their positions to tracking antennas on the earth. In addition, the transmitters are used for telemetry, the relaying of information from the scientific instruments aboard the satellite.Types of SatellitesSatellites can be divided into five principal types: research, communications, weather, navigational, and applications.Research satellites measure fundamental properties of outer space, e.g., magnetic fields, the flux of cosmic rays and micrometeorites, and properties of celestial objects that are difficult or impossible to observe from the earth. Early research satellites included a series of orbiting observatories designed to study radiation from the sun, light and radio emissions from distant stars, and the earth's atmosphere. Notable research satellites have included the Hubble Space Telescope, the Compton Gamma-Ray Observatory, the Chandra X-ray Observatory,the Infrared Space Observatory, and the Solar and Heliospheric Observatory (see observatory, orbiting). Also contributing to scientific research were the experiments conducted by the astronauts and cosmonauts aboard the space stations launched by the United States (Skylab) and the Soviet Union (Salyutand Mir); in these stations researchers worked for months at a time on scientific or technical projects. The International Space Station, whose first permanent crew boarded in 2000, continues this work.Communications satellites provide a worldwide linkup of radio, telephone, and television. The first communications satellite was Echo 1; launched in 1960, it was a large metallized balloon that reflected radio signals striking it. This passive mode of operation quickly gave way to the active or repeater mode, in which complex electronic equipment aboard the satellite receives a signal from the earth, amplifies it, and transmits it to another point on the earth. Relay 1 and Telstar 1, both launched in 1962, were the first active communications satellites; Telstar 1 relayed the first live television broadcast across the Atlantic Ocean. However, satellites in the Relay and Telstar program were not in geosynchronous orbits, which is the secret to continuous communications networks. Syncom 3, launched in 1964, was the first stationary earth satellite. It was used to telecast the 1964 Olympic Games in Tokyo to the United States, the first television program to cross the Pacific Ocean. In principle, three geosynchronous satellites located symmetrically in the plane of the earth's equator can provide complete coverage of the earth's surface. In practice, many more are used in order to increase the system's message-handling capacity. The first commercial geosynchronous satellite, Intelsat 1 (better known as Early Bird), was launched by COMSAT in 1965. A network of 29 Intelsat satellites in geosynchronous orbit now provides instantaneous communications throughout the world. In addition, numerous communications satellites have been orbited by commercial organizations and individual nations for a variety of telecommunications tasks.Weather satellites, or meteorological satellites, provide continuous, up-to-date information about large-scale atmospheric conditions such as cloud cover and temperature profiles. Tiros 1, the first such satellite, was launched in 1960; it transmitted infrared television pictures of the earth's cloud cover and was able to detect the development of hurricanes and to chart their paths. The Tiros series was followed by the Nimbus series, which carried six cameras for more detailed scanning, and the Itos series, which was able to transmit night photographs. Other weather satellites include the Geostationary Operational Environmental Satellites (GOES), which send weather data and pictures that cover a section of the United States; China, Japan, India, and the European Space Agency have orbited similar craft. Current weather satellites can transmit visible or infrared photos, focus on a narrow or wide area, and maneuver in space to obtain maximum coverage.Navigation satellites were developed primarily to satisfy the need for a navigation system that nuclear submarines could use to update their inertial navigation system. This led the U.S. navy to establish the Transit program in 1958; the system was declared operational in 1962 after the launch of Transit 5A. Transit satellites provided a constant signal by which aircraft and ships could determine their positions with great accuracy. In 1967 civilians were able to enjoy the benefits of Transit technology. However, the Transit system had an inherent limitation. The combination of the small number of Transit satellites and their polar orbits meant there were some areas of the globe that were not continuously covered-as a result, the users had to wait until a satellite was properly positioned before they could obtain navigational information. The limitations of the Transit system spurred the next advance in satellite navigation: the availability of 24-hour worldwide positioning information. The Navigation Satellite for Time and Ranging/Global Positioning Satellite System (Navstar/GPS) consists of 24 satellites approximately 11,000 miles above the surface of the earth in six different orbital planes. The GPS has several advantages over the Transit system: It provides greater accuracy in a shorter time; users can obtain information 24 hours a day; and users are always in view of at least five satellites, which yields highly accurate location information (a direct readout of position accurate to within a few yards) including altitude. In addition, because of technological improvements, the GPS system has user equipment that is smaller and less complex. The former Soviet Union established a Navstar equivalent system known as the Global Orbiting Navigation Satellite System (GLONASS). The Russian-operated GLONASS will use the same number of satellites and orbits similar to those of Navstar when complete. Many of the handheld GPS receivers can also use the GLONASS data if equipped with the proper processing software. Beidou is China's satellite-based navigation and global positioning system. It began operations is 2011 with 10 satellites, succeeding an experimental system that became operational in 2001, and is planned to utilize 35 satellites when completed in 2020.Applications satellites are designed to test ways of improving satellite technology itself. Areas of concern include structure, instrumentation, controls, power supplies, and telemetry for future communications, meteorological, and navigation satellites.Satellites also have been used for a number of military purposes, including infrared sensors that track missile launches; electronic sensors that eavesdrop on classified conversations; and optical and other sensors that aid military surveillance. Such reconnaissance satellites have subsequently proved to have civilian benefits, such as commercially available satellite photographs showing surface features and structures in great detail, and fire sensing in remote forested areas. The United States has launched several Landsat remote-imaging satellites to survey the earth's resources by means of special television cameras and radiometric scanners. The data from remote-imaging satellites has also been used in archaeological research. Russia and other nations have also launched such satellites; the French SPOT satellite provides higher-resolution photographs of the earth.BibliographySee M. V. Fox, Satellites (1996); S. A. Kallen, The Giant Leaps: The Race to Space (1996); M. Long, 1997 Phillips World Satellite Almanac (1997); A. Luther, Satellite Technology: An Introduction (2d ed. 1997).Cite this articlePick a style below, and copy the text for your bibliography.
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Why are ground stations in continuous contact with satellite in geostationary orbit?
Since the satellite appears fixed in the sky, antennas can also stay in a fixed position to communicate with it, and don't need to be continuously guided.
Why are satellites used to transmit TV programs?
There is an orbit called a geosynchronous orbit (GEO), which is a satellite that travels around the Earth in the Earth's exact speed, so it's always in the same position as the Earth. GEOs are used for communication nowadays, and so ground stations are always in contact with the satellites. That means that your T.V. programs and phone calls are never interrupted! :D
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