An artifical satellite is an object which has been placed into orbit by human endeavor. They are called artifical satellites to distinguish them from natural satellites like the Moon. Examples of artifical satellites are Communications Satellites and Monitering Satellites. The motion of a satellite or space-station is a direct consequence of Earth‘s gravity. Once launched in the appropriate orbit, these man-made crafts orbit around Earth without any propulsion. In this module, we shall study basics of satellite motion without going into details of the technology. Also, we shall develop analysis framework of artificial satellite, which can as well be extended to analysis of natural satellite like our moon. For the analysis here, we shall choose a simple framework of ―two – body‖ system, one of which is Earth. We should be aware that gravity is not the only force of gravitation working on the satellite, particularly if satellite is far off from Earth‘s surface. But, Earth being the closest massive body, its gravitational attraction is dominant to the extent of excluding effect of other bodies. For this reason, our analysis of satellite motion as ―isolated two body system‖ is good first approximation. Mass of artificial satellite is negligible in comparison to that of Earth. The ―center of mass‖ of the ―two body system‖ is about same as the center of Earth. There is possibility of different orbits, which are essentially elliptical with different eccentricity. A satellite close to the surface up to 2000 km describes nearly a circular trajectory. In this module, we shall confine ourselves to the analysis of satellites having circular trajectory only. Satellites are tracked by United States Space Surveillance Network (SSN), which has been tracking every object in orbit over 10 cm (3.937 inches) in diameter since it was founded in 1957. There are approximately 3,000 satellites operating in Earth orbit, according to the US National Aeronautics and Space Administration (NASA), out of roughly 8,000 man-made objects in total. In its entire history, the SSN has tracked more than 24,500 space objects orbitingEarth. The majority of these have fallen into unstable orbits and incinerated during reentry. The SSN also keeps track which piece of space junk belongs to which country. The SSN was founded in the wake of the launch of Sputnik, the first artificial satellite, by the Soviet Union in October 1957. Orbiting the planet at 20,000 mph (32,186.88 kph) while emitting a constant radio signal, Sputnik was a red flag that told America not to take its technological dominance for granted. In the following decade, the Space Race between the USSR and USA occurred, ending with Apollo landing in July 1969. As space technology matured, satellites were launched for military and commercial purposes. The price of satellite launches has dropped to as low as a few million dollars for light satellites, and a few tens of millions for heavy satellites. This put satellite technology within the reach of many nations and international companies.
The history of the artificial satellite:
An artificial satellite is one in which the satellite is created by man for example sputnik. On the other hand a non-artificial satellite is one in which it travels and was created natural and not by man. The meaning of ‗satellite' does not suggest that it is either a natural or unnatural thing satellite simply means ‗a celestial body that orbits a planet, for example a moon? The first artificial satellite was successfully launched by the Soviet Union on October 4th 1957, this satellite was called Sputnik 1. Sputnik 1 weighed 183 pounds, was about the size of a cricket ball and took 98 minutes to orbit the earth. The launch of this satellite; sputnik 1, has been named as the start of the space age and the start of the US-USSR space race which spaned over the years of the 1960‘s. The IGY (International Geophysical Year) was established in 1952 as the time spanning from the 1st of July 1957 until the 31st of December 1958. The IGY was established by the group known as the International Council of Scientific Unions. The reason for this establishment was because the International Council of Scientific Unions believed that throughout this time the cycles of solar activity would be at a high point. A resolution was adopted by the council calling that all artificial satellites be launched during the time of the IGY. This was in 1954 and the reason for this was to map the earth‘s surface over this time.
Plans announced by the White House proposing that an earth orbiting satellite be launched for the IGY. They received many proposals from many Government Research Agencies to develop this satellite but by September 1955 it was decided that the naval research Laboratories Vanguard proposal was the best one to represent the US during the IGY. But this idea was soon turned away from when the USSR launched Sputnik. This launch caught the attention of the world for the reason that the sputnik had a much more impressive size than Vanguard‘s intended 3.5 pound payload. Along with this launch came the fear that because the USSR now had the ability to launch satellites, it would be able to launch ballistic missiles containing nuclear devices to the US. The next launch was on November 3rd of that year when the Soviet‘s launched Sputnik 2. Sputnik 2 carried a much heavier payload. This included a dog called Laika. Immediately after Sputnik I was launched, the US Defence Department responded by funding another satellite project run by a man named Von Braun. Von Braun, his team and the US Army arsenal at Redstone worked on what was the Explorer Project. It was not until January 31st that Explorer I was launched. It contained a small, scientifically important payload which is responsible for discovering the magnetic radiation belts around the earth. These were named after the principal investigator James Van Allen. The explorer program continued creating a series of successful lightweight scientific spacecraft.
In July 1958 the National Aeronautics and Space Act was passed by congress, more commonly known as the space Act; creating NASA (The National Aeronautics and Space Administration) from the National Advisory Committee for Aeronautics (NACA) and other government agencies. NASA was official as of October 1958
Speed of the satellite
Satellites have specific orbital speed to move around Earth, depending on its distance from the center of Earth. The satellite is launched from the surface with the help of a rocket, which parks it in particular orbit with a tangential speed appropriate for that orbit. Since satellite is orbiting along a circular path, there is requirement for the provision of centripetal force, which is always directed towards the center of orbit. This requirement of centripetal force is met by the force of gravity. Hence,
Figure 1: Gravitational attraction provides for the requirement of centripetal force for circular motion of satellite.
The satellites are made to specific tasks. One of the most significant applications of artificial satellite is its use in telecast around the world. Earlier it was difficult to relay telecast signals due to spherical shape of Earth. In recent time, advancements in communication have brought about astounding change in the way we live. The backbone of this communication wonder is variety of satellite systems orbiting around Earth. Satellite systems are classified for different aspects of satellite motion. From the point of physics, it is the orbital classification of satellite systems, which is more interesting. Few of the famous orbits are described here. Almost all orbits generally describe an elliptical orbit. We shall discuss elliptical orbits in the module dedicated to Kepler‘s law. For the present, however, we can approximate them to be circular for analysis purpose.
1: Geocentric orbit : It is an orbit around Earth. This is the orbit of artificial satellite, which is launched to revolve around Earth. Geocentric orbit is further classified on the basis of distance from Earth‘s surface (i) low Earth orbit up to 2000 km (ii) middle Earth orbit between 2000 and geo-synchronous orbit (36000 km) and (iii) high Earth orbit above geo-synchronous orbit (36000 km). 2: Heliocentric Orbit : It is an orbit around Sun. The orbits of planets and all other celestial bodies in the solar system describe heliocentric orbits. 3: Geosynchronous Orbit : The time period of this orbit is same as the time period of Earth. 4: Geostationary Orbit : The plane of rotation is equatorial plane. The satellite in this orbit has time period equal to that of Earth. Thus, motion of satellite is completely synchronized with the motion of Earth. The sense of rotation of the satellite is same as that of Earth. The satellite, therefore, is always above a given position on the surface. The orbit is at a distance of 36000 km from Earth‘s surface and about 42400 (= 36000 + 6400) km from the center of Earth. The orbit is also known as Clarke‘s orbit after the name of author, who suggested this orbit. 5: Molniya Orbit – It is an orbit having inclination of 63.4° with respect to equatorial plane and orbital period equal to half that of Earth. 6: Polar orbit : The orbit has an inclination of 90° with respect to the equatorial plane and as such, passes over Earth‘s poles. Another important classification of satellite runs along the uses of satellites. Few important satellite types under this classification are : 1: Communication satellites : They facilitate communication around the world. The geostationary satellite covers ground locations, which are close to equator. Geostationary satellites appears low from a positions away from equator. For locations at different latitudes away from equator, we need to have suitably designed orbits so that the area can be covered round the clock. Molniya orbit is one such orbit, which is designed to provide satellite coverage through a satellite system, consisting of more than one satellite. 2: Astronomical satellites : They are designed for studying celestial bodies. 3: Navigational satellites : They are used to specify location on Earth and develop services based on navigation. 4: Earth observation satellites : They are designed for studying Earth system, environment and disaster management. 5: Weather satellites : They facilitate to monitor weather and related services. 6: Space station : It is an artificial structure in space for human beings to stay and do assigned experiments/works
As a matter of fact, there is quite an elaborate classification system. We have only named few important satellite systems. In particular, there are varieties of satellite systems, including reconnaissance satellites, to meet military requirement. Satellites are objects orbiting a planet. The moon is a natural satellite. Artificial satellites are those put into orbit by man. The first artificial satellite was Sputnik I launched by the Soviet Union in 1957. Now almost fifty years later there are thousands of satellites orbiting the Earth at various heights. There are various kinds of satellites. The satellites called communications satellites are used to relay telephone messages and radio and television signals. It is such satellites that have made it possible for us to see on TV, live, cricket and tennis matches being played in Europe or Australia. Formerly one had to wait till the next day to see the recorded version. Some artificial satellites carry instruments that gather and send back information about the earth and its surroundings. This information is of immense value to weather forecasters, scientists, military planners and farmers and fishermen just to name a few. A major effort is on to study the earth and all ecological changes taking place on earth through satellites. Satellites can provide ecologists with detailed images of every square metre of the earth's surface for study. As there is no air in outer space and therefore no air resistance, satellites do not have to be sleek and streamlined, like rockets. So they come in a variety of shapes depending on the job they have to do.
Sputnik and The Dawn of the Space Age
History changed on October 4, 1957, when the Soviet Union successfully launched Sputnik I. The world's first artificial satellite was about the size of a beach ball (58 cm.or 22.8 inches in diameter), weighed only 83.6 kg. or 183.9 pounds, and took about 98 minutes to orbit the Earth on its elliptical path. That launch ushered in new political, military, technological, and scientific developments. While the Sputnik launch was a single event, it marked the start of the space age and the U.S.-U.S.S.R space race.
The story begins in 1952, when the International Council of Scientific Unions decided to establish July 1, 1957, to December 31, 1958, as the International Geophysical Year (IGY) because the scientists knew that the cycles of solar activity would be at a high point then. In October 1954, the council adopted a resolution calling for artificial satellites to be launched during the IGY to map the Earth's surface. In July 1955, the White House announced plans to launch an Earth-orbiting satellite for the IGY and solicited proposals from various Government research agencies to undertake development. In September 1955, the Naval Research Laboratory's Vanguard proposal was chosen to represent the U.S. during the IGY. The Sputnik launch changed everything. As a technical achievement, Sputnik caught the world's attention and the American public off-guard. Its size was more impressive than Vanguard's intended 3.5-pound payload. In addition, the public feared that the Soviets' ability to launch satellites also translated into the capability to launch ballistic missiles that could carry nuclear weapons from Europe to the U.S. Then the Soviets struck again; on November 3, Sputnik II was launched, carrying a much heavier payload, including a dog named Laika. Immediately after the Sputnik I launch in October, the U.S. Defense Department responded to the political furor by approving funding for another U.S. satellite project. As a simultaneous alternative to Vanguard, Wernher von Braun and his Army Redstone Arsenal team began work on the Explorer project. On January 31, 1958, the tide changed, when the United States successfully launched Explorer I. This satellite carried a small scientific payload that eventually discovered the magnetic radiation belts around the Earth, named after principal investigator James Van Allen. The Explorer program continued as a successful ongoing series of lightweight, scientifically useful spacecraft. The Sputnik launch also led directly to the creation of National Aeronautics and Space Administration (NASA). In July 1958, Congress passed the National Aeronautics and Space Act (commonly called the "Space Act"), which created NASA as of October 1, 1958 from the National Advisory Committee for Aeronautics (NACA) and other government agencies.
The Soviet space program was tied to the USSR's Five-Year Plans and from the start was reliant on support from the Soviet military. Although he was "single-mindedly driven by the dream of space travel", Korolyov generally kept this a secret while working on military projects— especially, after the Soviet Union's first atomic bomb test in 1949, a missile capable of carrying a nuclear warhead to the United States—as many mocked the idea of launching satellites and manned spacecraft. Nonetheless, the first Soviet rocket with animals aboard launched in July 1951; the two dogs were recovered alive after reaching 101 km in altitude. Two months ahead of America's first such achievement, this and subsequent flights gave the Soviets valuable experience with space medicine.
Because of its global range and large payload of approximately five tons, the reliable R-7 was not only effective as a strategic delivery system for nuclear warheads, but also as an excellent basis for a space vehicle. The United States' announcement in July 1955 of its plan to launch a satellite during the International Geophysical Year greatly benefited Korolyov in persuading Soviet leader Nikita Khrushchev to support his plans in January 1956, in order to surpass the Americans Plans were approved for Earth-orbiting satellites (Sputnik) to gain knowledge of space, and four unmanned military reconnaissance satellites, Zenit. Further planned developments called for a manned Earth orbit flight by 1964 and an unmanned lunar mission at an earlier date. After the first Sputnik proved to be a successful propaganda coup, Korolyov—now known publicly only as the mysterious "Chief Designer of Rocket-Space Systems":168-169—was charged to accelerate the manned program, the design of which was combined with the Zenit program to produce the Vostok spacecraft. Still influenced by Tsiolkovsky—who had chosen Mars as the most important goal for space travel—in the early 1960s the Russian program under Korolyov created substantial plans for manned trips to Mars as early as 1968 to 1970. With closed-loop life support systems and electrical rocket engines, and launched from large orbiting space stations, these plans were much more ambitious than America's goal of landing on the moon An Artificial satellite is a manufactured object that continuously orbits a body in space, usually the Earth. They are used for a variety of reasons ranging from studying the universe to assisting in navigation of ships and aircraft. Through these uses artificial satellites strengthen or provide communications, monitoring of crops or other natural resources,and the knowledge of weather or astronomy. Artificial satellites usually are built to perform their function. A communications satellite for example usually is an umbrella - shaped dish like structure with multiple antennas spiking out of it. Artificial satellites remain in orbit because of the precision of the satellites velocity in reference to the gravitational force between it and the earth. The artificial satellites were first manufactured by the Soviets in a project called Sputnik 1 in 1957. From there, artificial satellites became the phenomena they are now. They are vital structures in the development of our planet and in the future, they will play an even bigger role in our lives.
Types of Satellites
Satellites 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 (Salyut and Mir); in these stations researchers worked for months at a time on scientific or technical projects. The International Space Station, currently under construction, will continue 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. 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. Russia and other nations have also launched such satellites; the French SPOT satellite provides higher-resolution photographs of the earth.
ADVANTAGES 1)Used in long distance communications such as in television,fax,internet etc 2)Used in television and radio broadcasting etc 3)Weather forcasting (i.e) in prediction of rainfall,snowfall,storm etc 4)Agricultural monitoring(i.e)crop disease,crop failure. 5)Collecting information about other planets,stars and other celestial bodies