Satellites

Satellites Overview History Launching of Satellites How Satellites Work Orbit Distance Types: Low-Earth-Orbit (LEOs) Medium-Earth-Orbit (MEOs) Global Positioning System (GPS) Geostationary (GEOs) Applications

History of Satellites The First Satellites The theory of satellites was simple enough - shoot something out into space at the right speed and on the correct trajectory and it will stay up there, orbiting Earth, for years - if not forever. If the orbit is the right distance in space the satellite will keep pace with the rotation of the Earth. Pioneer Satellites (1957) Early in October 1957 communications stations started picking up a regular beeping noise coming from space. The signals were coming from Russia's Sputnik 1, the world's first man-made satellite. It was January 1958, before a Jupiter rocket successfully launched Explorer 1, the first American satellite. 

History of Satellites On October 4, 1957, the Soviet Union successfully launched Sputnik I. The world's first artificial satellite was about the size of a basketball, weighed only 183 pounds, and took about 98 minutes to orbit the Earth on its elliptical path on November 3, Sputnik II was launched On January 31, 1958, the United States successfully launched Explorer I

History of Satellites NASA's Syncom programme (1963) GEOs In July 1963 the Hughes Aircraft Corporation launched the experimental Syncom 2 for NASA, the world's first geosynchronous communications satellite. Its earlier sister, Syncom 1, had been blown up on launch earlier that year, but the second version was a huge success. It carried the first live two-way satellite call between heads of state when President John F. Kennedy in Washington, D.C., telephoned Nigerian Prime Minister Abubaker Balewa in Africa. The third Syncom satellite transmitted live television coverage of the 1964 Olympic Games from Tokyo.  

History of Satellites Early Bird (1965) The world's first commercial communications satellite was Early Bird, built for the Communications Satellite Corporation (COMSAT) by Hughes. The satellite was launched on April 6, 1965, and placed in commercial service after moving into geosynchronous orbit 22,300 miles above the equator. That meant it was always on station to provide line of sight communications between Europe and North America. Early Bird didn't have a battery - and worked only when its solar panels were exposed to the sun.

History of Satellites Later communications satellites The launch of the Intelsat 3 satellites in 1969 created a global TV and speech communications network that spanned the Atlantic, Pacific and Indian Oceans. The introduction of multiple-beam antennas in the 1980s brought new improvements in efficiency, as a satellite's power could now be concentrated on small regions of the Earth, making possible smaller-aperture (coverage area), lower-cost ground stations. The Capacity (the number of simultaneous television and speech channels carried) grew as well.

1957 First Artificial Satellite (Sputnik) The first artificial satellite was Sputnik 1, launched by the Soviet Union on October 4, 1957. At about the size of a basketball, Sputnik 1 was equipped with a radio transmitter that gave off a beeping signal—helping the Soviets to track it on its 98-minute orbit and to signal to the world that the U.S.S.R. was the leader in space

Photograph courtesy NOAA/NESDIS Headquarters 1960 First Orbiting Observations (TIROS-1 Weather Satellite) The first aerial images of the Earth from space were taken by TIROS 1 (Television InfraRed Observation Satellite). TIROS 1 was launched in 1960 to find out if it was possible to watch cloud cover and weather patterns from space. Although it was an experimental satellite, TIROS images were immediately put to use by meteorologists

First Surveying Satellite (Landsat) 1972 First Surveying Satellite (Landsat) The first Landsat satellite was called the Earth Resources Technology Satellite, or ERTS. Since its launch on July 23, 1972, six Landsats have followed, with the latest, Landsat 7, lifting off on April 15, 1999. Over the years successive Landsats have not only carried better land-viewing sensors, but they have created a valuable archive of images that are being used to see how the land is changing over the years. Landsat 7 carries the Enhanced Thematic Mapper Plus, which scans the Earth in eight bands of visible and invisible light

1974 First Geostationary Satellite (GOES) Best known as weather satellites, the first GOES (Geostationary Operational Environmental Satellite) was launched on October 16, 1975. Their high orbits and visible-light and infrared sensors allow for constant surveillance of weather patterns over the entire planet and have enabled GOES to revolutionize the science of weather prediction. GOES-10, launched in 1998, images the 48 contiguous U.S. states every five minutes.

Launching of Artificial Satellite

To enable a satellite to orbit around any planet, we have to consider height from which the satellite must be thrown. Consider yourself, if you throw a stone, it comes to earth after some time, why? It is because of the gravitational attraction of earth and the stone. By the Newton 's law of gravitation, stone and earth would be attracted towards each other by force F = GMm / R2 Where M is mass of earth m is mass of stone R is distance between centre of earth and stone

Since, throwing the satellite from earth's surface will make the satellite to come down to earth's surface due to gravitational pull F  1/ R2 i.e. greater is the distance, lesser the force of attraction. As we have seen earlier that value of g decreases with increase in height and expression is given by gh / g = g ( 1 - 2h / R ) We can say that to put on object into earth's orbit. •  Move the object to suitable height. •  Then, project it with high velocity. Remember, less the height to which object is moved, greater the velocity needed for projecting. I would like to state that the velocity that I was talking about is called as ‘ ORBITAL VELOCITY

Satellite  A Satellite is a solid object which revolves around some heavenly body due to the effect of gravitational forces which are mutual in nature. We can categorize satellites in two types, namely Passive Satellites and Active satellites. A passive satellite can be further subdivided into two types, namely Natural satellites and artificial satellites. A moon is a natural satellite of earth. But spherical balloon with metal coated plastic serve as artificial satellites.  Active satellites are complicated structures having a processing equipment called Transponder which is very vital for functioning of the satellite. These transponders serve dual purpose i.e. provides amplification of the incoming signal and performs the frequency translation of the incoming signal to avoid interference between the two signals.   

How Satellites Work A Earth Station sends message in GHz range. (Uplink) Satellite Receive and retransmit signals back. (Downlink) Other Earth Stations receive message in useful strength area. (Footprint)

Microwaves are electromagnetic waves with frequency from 30MHz to 1 GHz. The ionosphere cannot reflect microwaves back to the earth. They pass through the ionosphere A satellite used to receive microwaves and then transmit them back to the earth. Satellites provide links in two ways. Firstly a satellite provide point to point communication link between one ground station and the other. One ground station transmit signal to the other satellite and next ground station receives them from the satellite. Secondly, satellite receives signals from one ground station and transmits to them to the number of ground receivers. Most satellite use frequency bandwidth through from 5.92 to 6.4GHz from transmission of data from earth to the satellite and a frequency bandwidth from 3.7 to 4.1GHz for transmission from satellite to the earth.

Water discovered on moon

Low-Earth-Orbit (LEO) Altitude (375-1000 miles) Revolution time: 90 min - 3 hours. Advantages: Reduces transmission delay Eliminates need for bulky receiving equipment. Disadvantages: Smaller coverage area. Shorter life span (5-8 yrs.) than GEOs (10 yrs).

Middle-Earth-Orbiting (MEO) MEOs orbits between the altitudes of 5,600 and 9,500 miles. These orbits are primarily reserved for communications satellites that cover the North and South Pole. Unlike the circular orbit of the geostationary satellites, MEOs are placed in an elliptical (oval-shaped) orbit.

A constellation of 24 satellites GPS: What is it ? A constellation of 24 satellites The Global Positioning System (GPS) is a space-based global navigation satellite system (GNSS) that provides reliable location and time information in all weather and at all times and anywhere on or near the Earth The Global Positioning System (GPS) is a worldwide radio-navigation system formed from a constellation of 24 satellites and their ground stations. They are constantly moving, making two complete orbits in less than 24 hours. These satellites are traveling at speeds of roughly 7,000 miles an hour. GPS Satellites Name: NAVSTAR Manufacturer: Rockwell International Altitude: 10,900 nautical miles Weight: 1900 lbs (in orbit) Size: 17 ft with solar panels extended Orbital Period: 12 hours Orbital Plane: 55 degrees to equatorial plane Planned Lifespan: 7.5 years Current constellation: 24 Block II production satellites The spacing of the satellites are arranged so that a minimum of five satellites are in view from every point on the globe.

Geosynchronous-Earth-Orbit (GEO) Orbit is sychroneous with the earths rotation. From the ground the satellite appears fixed. Altitude is about 23,000 miles. Coverage to 40% of planet per satellite.

Basics of GEOs Geostationary satellites are commonly used for communications and weather-observation.The typical service life expectancy of a geostationary satellite is 10-15 years. Because geostationary satellites circle the earth at the equator, they are not able to provide coverage at the Northernmost and Southernmost latitudes. Advantages: Weather images can be displayed. Television broadcasts are uninterrupted. Used to track major developments such as hurricanes 24 hours a day. Disadvantages: It takes longer for the signal to get to earth and back to satellite. Increased difficulty of telephone conversations. GEOs are not positioned in the farthest northern and southern orbits.

India to Launch 3D Weather Forecasting Satellite in 2011 Applications India uses its satellites communication network – one of the largest in the world – for applications such as land management, water resources management, natural disaster forecasting, radio networking, weather forecasting, meteorological imaging and computer communication The INSAT-2 satellites also provide telephone links to remote areas; data transmission for organizations such as the mobile satellite service communications for private operators, railways and road transport; and broadcast satellite services, used by India’s state-owned television agency as well as commercial television channels ISRO has applied its technology to "telemedicine", directly connecting patients in rural areas to medical professionals in urban locations via satellites Since high-quality healthcare is not universally available in some of the remote areas of India, the patients in remote areas are diagnosed and analyzed by doctors in urban centres in real time via video conferencing INSAT-4CR was launched on 2 September 2007 by GSLV-F04. It is a replacement satellite of INSAT-4C which was lost when GSLV-F02 failed and had to be destroyed on its course This satellite is used by Airtel Digital TV and Sun Direct DTH to broadcast their DTH services. India to Launch 3D Weather Forecasting Satellite in 2011  

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