Satellite Communication PDF

SATELLITE COMMUNICATION SATELLITE COMMUNICATION - SATELLITE COMMUNICATION IS TRANSPORTING INFORMATION FROM ONE PLACE TO ANOTHER USING A COMMUNICATION SATELLITE IN ORBIT AROUND THE EARTH. COMMUNICATION SATELLITE - IS AN ARTIFICIAL SATELLITE THAT TRANSMITS THE SIGNAL VIA A TRANSPONDER...

SATELLITE COMMUNICATION SATELLITE COMMUNICATION - SATELLITE COMMUNICATION IS TRANSPORTING INFORMATION FROM ONE PLACE TO ANOTHER USING A COMMUNICATION SATELLITE IN ORBIT AROUND THE EARTH. COMMUNICATION SATELLITE - IS AN ARTIFICIAL SATELLITE THAT TRANSMITS THE SIGNAL VIA A TRANSPONDER BY CREATING A CHANNEL BETWEEN THE TRANSMITTER AND THE RECEIVER AT DIFFERENT EARTH LOCATIONS. Satellite  In simple terms, a satellite is smaller object or body that revolves around a much larger object in space in a fixed well defined path.  An object orbiting around the sun, earth or any other colossal body  Two Major Types of Satellites 1.Natural Satellites -Not Man made (Examples: planets, moons, and comets) 2. Man-made or Artificial Satellites -specifically designed and launched into space for variety of purposes such as weather monitoring,navigation,tv,mobile communication,planetary research etc. (Example: Sputnik-I, Explorer 1, INSAT, IRS, Edusat, GSat, Chandrayaan etc.) Types of Artificial Satellite 1. Geostationary Satellite - placed into orbit at a distance of around 35,800 km from the earth’s surface - they rotate in the same direction as the earth and one revolution of such satellites is the same as one day on earth (roughly 24 hours) - used as communication satellites and for weather-based applications. 2. Polar Satellite - satellites that orbit around the earth in approximately 500- 800 km away orbits. - revolve around the earth in a north-south direction around the earth as opposed to east-west like the geostationary satellites. - They are very useful in applications where the field vision of the entire earth is required in a single day. - They are used in weather applications where predicting weather and climate-based disasters can be done in a short time. They are also used as relay stations. 3. Low Earth Orbit (LEO) Satellites - moving at an altitude of roughly 160–1,500 kilometers above the Earth’s surface. - They have a short orbital period, between 90 and 120 minutes, meaning they can travel around the planet up to 16 times a day. - This makes them particularly well-suited to all types of remote sensing, high-resolution earth observation, and scientific research, as data can be acquired and transmitted rapidly. 4. Medium Earth Orbit (MEO) Satellites - located between low Earth and geostationary orbits, typically at an altitude of about 5,000 to 20,000 kilometers. - Positioning and navigation services, like GPS, extensively use MEO type of satellites. - Recently, high-throughput satellite (HTS) MEO constellations have been put into operation to enable low-latency data communication to service providers, commercial and government organizations. - With their longer orbital period (usually between 2 and 12 hours), this type of satellites offer a happy medium between coverage area and data transmission rates. - Compared to low Earth orbit spacecraft, MEO ones require fewer devices to give worldwide coverage, but their time delay is longer and their signals are weaker. 5.Geostationary Transfer Orbit (GTO) Satellites -The most frequent type of satellite transfer orbit is a geostationary one utilized to migrate from a transition orbit to GEO. Spacecraft are not always placed directly into their ultimate orbit when propelled from Earth into space by launch vehicles such as Falcon 9. Rockets carrying payload to GEO drop it off at transfer orbits, which are halfway points on the path to its final position. Then a satellite’s engine fires to reach its destination orbit and adjust its inclination. This shortcut allows the machine to reach geostationary orbit with minimal resources. Other, less common orbit types include the highly elliptical orbit (HEO), polar orbit, and Lagrange point (L- point). The objectives and tasks of the spacecraft will dictate the orbital type chosen. Because of this, there should be more thought given to satellite types by applications. Some important uses of artificial satellites are: 1.Telecommunication: The satellites are used for telecommunication purposes through telephone, television, mobile phones, internet services, etc. where signals are received from different locations across the globe and transmit to other parts of the world. 2. Monitoring: This is used to secure important information about geological and meteorological areas even agriculture monitoring i.e. crop production, disease and failure in particular areas. 3.It helps scientists to stay updated about droughts and food production and to estimate the loss from these calamities. 4. Artificial satellites help in discovering underground water reserves and contribute to water management. 5. It also helps in identifying the exact location of an airplane, a ship, a person, and  The GPS orbiting satellites (global positioning of 20000 at a heightsystem) consists 20000 of 2424 satellites kilometres orbiting above the at asurface. Earth's height of 20000 A GPS 20000 kilometres receiver's above exact position on the Earth's Earth surface.using is calculated A GPSthe receiver's exai difference 24 satellites orbiting at a height of 2000020000 kilometres above the Earth's surface. A GPS receiver's exact position on Earth is calculated using the difference ypes of Satellites on the Basis Of Their Applicatio 1.Navigation satellites 2.Communication satellites 3.Weather satellites 4.Military satellites 5.Earth Observation satellites, 6.Astronomical satellites, 7.International Space Station, 8. Remote Sensing satellites, 9.Global Positioning satellites 1.Navigational Satellites -The GPS (global positioning system) consists of 24 satellites orbiting at a height of 20000 kilometers above the Earth's surface. A GPS receiver's exact position on Earth is calculated using the difference in time between signals obtained from four satellites. 2. Communication Satellites -The Optus D1 satellite, for example, is in a geostationary orbit above the equator and has a coverage footprint that covers all of Australia and New Zealand, and is used for television, phone, and internet transmissions. 3. Weather Satellites: -These are used to photograph clouds as well as to determine temperature and rainfall. Depending on the type of weather satellite, both geostationary and low Earth orbits are used. Weather satellites are used to improve weather forecasting accuracy. 4. Military Satellites -is an artificial satellite used for a military purpose. The most common missions are intelligence gathering, navigation and military communications.. 5. Earth observation Satellites - The Earth is photographed and imaged using these. Low Earth orbits are primarily used to create a more accurate image. 6. Astronomical Satellites -These are used to keep track of and visualise space. The Hubble Space Telescope, for example, orbits at 600 kilometers altitude and offers extremely sharp images of stars and distant galaxies. Spitzer and Chandra are two other space telescopes. 7. International Space Stations (ISS) -This is a habitable space station. The International Space Station (ISS) orbits the Earth every 92 minutes at a speed of 28000 kilometers per hour from a height of 400 kilometers. In a microgravity environment, scientists aboard the International Space Station will conduct a variety of useful experiments. 8. Earth observation satellite or Earth remote sensing satellite - is a satellite used or designed for Earth observation (EO) from orbit, including spy satellites and similar ones intended for non- military uses such as environmental monitoring, meteorology, cartography and others. The most common type are Earth imaging satellites, that take satellite images, analogous to aerial photographs; some EO satellites may perform remote The International Space Station (ISS) was launched into orbit in 1998. It is a habitable artificial satellite and sometimes can be seen on nights with a clear sky. It functions as a lab, observatory, and a landing base for possible expeditions. 9. The Global Positioning System (GPS) Satellite - originally Navstar GPS, is a satellite-based radio navigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite systems (GNSS) that provide geolocation and time information to a GPS receiver anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites.  BRIEF HISTORY OF SATELLITE  The first published mathematical study of the possibility of an artificial satellite was Newton's cannonball, a thought experiment by Isaac Newton to explain the motion of natural satellites, in his Philosophiæ Naturalis Principia Mathematica (1687). Sputnik 1- First artificial satellite launched into the Earth's orbit by the Soviet Union on October 4, 1957 Sputnik 2 - the Soviets launched an even more massive satellite which carried the dog Laika on Nov. 3, 1957 Explorer 1 – America’s first satellite that was launched on Jan. 31, 1958. Sputnik 1 Sputnik 2 Explorer 1 BASIC PARTS OF A SATELLITE 1. Power system (which could be solar or nuclear) 2. a way to control its attitude 3. an antenna to transmit and receive information 4. a payload to collect information (such as a camera or particle detector). Satellite Design Every satellite has some of the same basic parts: 1. The bus – this is the frame and structure of the satellite to which all the other parts are attached. 2. power source – most satellites have solar panels to generate electricity. Batteries store some of this energy for times that the satellite is in the shadow of the Earth. 3. Heat control system – satellites are exposed to extremely high temperatures due to exposure to the Sun. There needs to be a way to reflect and reradiate heat. Electrical components of the satellite can also produce a lot of heat. 4. Computer system – satellites need computers to control how they operate and also to monitor things like altitude, orientation and temperature. 5. Communication system – all satellites need to be able to send and receive data to ground stations on Earth or to other satellites. Curved satellite dishes are used as antennae 6. Attitude control system – this is the system that keeps a satellite pointed in the right direction. Gyroscopes and rocket thrusters are commonly used to change orientation. Light sensors are commonly used to determine what direction a satellite is pointing. 7. A propulsion system – a rocket engine on the satellite may be used to help place the satellite into the correct orbit. Once in orbit, satellites do not need any rockets to keep them moving. However, small rockets called thrusters are used if a satellite needs to change orbit slightly. WHAT KEEPS A SATELLITE FROM FALLING TO EARTH? A satellite is best understood as a projectile, or an object that has only one force acting on it — gravity. Technically speaking, anything that crosses the Karman Line at an altitude of 100 kilometers (62 miles) is considered in space. However, a satellite needs to be going fast — at least 8 km (5 miles) a second — to stop from falling back down to Earth immediately. If a satellite is traveling fast enough, it will perpetually "fall" toward Earth, but the Earth's curvature means that the satellite will fall around our planet instead of crashing back on the surface. Satellites that travel closer to Earth are at risk of falling because the drag of atmospheric molecules will slow the satellites down. Those that orbit farther away from Earth have fewer molecules to contend with. There are several accepted "zones" of orbits around the Earth. One is called low-Earth-orbit, which extends from about 160 to 2,000 km (about 100 to 1,250 miles). This is the zone where the ISS orbits and where the space shuttle used to do its work. In fact, all human missions except for the Apollo flights to the moon took place in this zone. Most satellites also work in this zone. WHAT STOPS A SATELLITE FROM CRASHING INTO ANOTHER SATELLITE? There are an estimated half-million artificial objects in Earth orbit today, ranging in size from paint flecks up to full-fledged satellites — each traveling at speeds of thousands of miles an hour. Only a fraction of these satellites are useable, meaning that there is a lot of "space junk" floating around out there. With everything that is lobbed into orbit, the chance of a collision increases. Space agencies have to consider orbital trajectories carefully when launching something into space. Agencies such as the United States Space Surveillance Network keep an eye on orbital debris from the ground, and alert NASA and other entities if an errant piece is in danger of hitting something vital. This means that from time to time, the ISS needs to perform evasive maneuvers to get out of the way. Collisions still occur, however. One of the biggest culprits of space debris was the leftovers of a 2007 anti-satellite test performed by the Chinese, which generated debris that destroyed a Russian satellite in 2013. Also that year, the Iridium 33 and Cosmos 2251 satellites smashed into each other, generating a cloud of debris. NASA, the European Space Agency and many other entities are considering measures to reduce the amount of orbital debris. Some suggest bringing down dead satellites in some way, perhaps using a net or air bursts to disturb the debris from its Circular Motion Principles for Satellites 1. A Satellite is a Projectile The fundamental principle to be understood concerning satellites is that a satellite is a projectile. That is to say, a satellite is an object upon which the only force is gravity. Once launched into orbit, the only force governing the motion of a satellite is the force of gravity.  Newton’s Cannon Ball Experiment Newtons Cannon ball was a thought expirement Isaac Newton used to explain the principle of orbital motion It was the first explanation of an orbit and the easiest to understand Newtons visualize a cannon on top of a tall mounbtain where there is no air or at least that it is endowed with little or no power of resisting".  As a gravitational force acts on the projectile, it will follow a different path depending on its initial velocity.  If the speed is low, it will simply fall back on Earth.  If the speed is the orbital speed at that altitude, it will go on circling around the Earth along a fixed circular orbit "and return to the mountain from which it was projected".  If the speed is higher than the orbital velocity, but not high enough to leave Earth altogether (lower than the escape velocity), it will continue revolving around Earth along an elliptical orbit.  If the speed is very high, it will leave Earth in a parabolic (at exactly escape velocity) or hyperbolic trajectory.  A satellite is acted upon by the force of gravity and this force does accelerate it towards the Earth.  In the absence of gravity a satellite would move in a straight line path tangent to the Earth.  In the absence of any forces whatsoever, an object in motion (such as a satellite) would continue in motion with the same speed and in the same direction. This is the law of inertia.  The force of gravity acts upon a high speed satellite to deviate its trajectory from a straight-line inertial path. Indeed, a satellite is accelerating towards the Earth due to the force of gravity. Satellite Motion Mathematics Solution: Solution: Solution: Kepler’s Law of Planetary Motion  Kepler’s Law  A set of three eperical expressioned that explained planetary motion in orbit around the sun  Published by Johannese Kepler between 1609 to 1619  They are called Kepler’s Law of Planetary Motion  The laws modified the heliocentric theory of Nicolaus Copernicus, replacing its circular orbits and epicycles with elliptical trajectories, and explaining how planetary velocities vary. The Three Laws state that: 1. The orbit of a planet is an ellipse with the Sun at one of the two foci. 2. A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time 3. The square of a planet's orbital period is proportional to the cube of the length of the semi-major axis of its orbit.  The elliptical orbits of planets were indicated by calculations of the orbit of Mars. From this, Kepler inferred that other bodies in the Solar System, including those farther away from the Sun, also have elliptical orbits. The second law helps to establish that when a planet is closer to the Sun, it travels faster. The third law expresses that the farther a planet is from the Sun, the slower its orbital speed, and vice versa. Kepler’s First Law “The orbit of a planet is an ellipse with the Sun at one of the two foci”  According to Kepler’s First Law, the path followed by satellite around Earth will be an ellipse  The center of the Earth will lie on one of the foci of the ellipse  A circular orbit is a special case of an elliptical orbit Kepler’s Second Law “A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time”  According to Kepler’s 2nd Law, a satellite will cover equal areas in its orbital plane for equal time interval Kepler’s Third Law “The square of a planet's orbital period is proportional to the cube of the length of the semi-major axis of its orbit” Sample Problem: 1. A Satellite orbits a large 4.178 kg planet and it takes 4.32 xs to compete its orbit. The radius of the planet is 5000 km. Determine the total radius, altitude of satellite and orbital speed of satellite. 2. A space station orbits at an altitude of 400 km above the surface of the Earth. Determine the space station’s orbital velocity using Planetary Formulas. Satellite Orbit and Trajectories