Published on February 13, 2008
Slide1: Presented by: ‘Leye Salu, CSSTE, OAU, Ile-Ife 16th August, 2007 Slide2: What exactly is a satellite? Various types of satellites How are satellites placed in their various orbits? What are the types of orbit available? What are the various uses to which satellites can be put? How does a typical satellite carry out its functions? Issues arising from satellite use What exactly is a satellite?: What exactly is a satellite? The word satellite originated from the Latin word “Satellit”- meaning an attendant, one who is constantly hovering around & attending to a “master” or big man. For our own purposes however a satellite is simply any body that moves around another (usually much larger) one in a mathematically predictable path called an orbit Types of satellite orbits: Types of satellite orbits Polar Orbit Inclined orbit Geostationary orbit Molniya orbit Elliptical orbit Types of satellite orbits II: Low Earth Orbit (LEO) Medium Earth Orbit(MEO) Geostationary Earth Orbit (GEO) High Earth Orbit (HEO) Types of satellite orbits II Satellite orbits are also classified based on their heights above the earth: Types of satellite: Types of satellite Remote sensing satellites: Remote sensing satellites These “look” down on the earth from a great height and can thus see much more detail depending on height above the earth’s surface Remote sensing can be thought of as the science of obtaining information about an object of interest without being in physical contact with it Slide8: Earth Observation Satellites look down on the earth’s surface, the sensor or camera has a slit through which light enters just like a normal camera. The satellites reflection moves along the earth’s surface- this is called the ground track. Along the ground track the satellite takes pictures in a long thin strip called a “swathe line”. The smallest area of the strip or swathe is known as the “resolution” of the satellite. The smaller the resolution of a satellite the more the detail it can see though it sees a smaller area Slide9: As remote sensing satellites look down on the earths surface, they carry instruments that see various types of light ranging from infrared to visible light and even radar imagery! These images are transmitted as digital data to earth stations(easily recognizable by satellite dishes). These stations process, store and distribute the data for analysis. Depending on the kind of band(I.e. “Light”) used different kinds of information can be obtained from a remote sensing satellite Slide10: Meteorological Satellites Satellite image from a meteorological satellite showing a Hurricane. Note the clearly visible eye of the hurricane. A storm such as this can be observed right from its early stages to its end; its path can be predicted and so millions of lives potentially saved through a satellite based early warning system Slide11: Often satellites also act as collection and distribution points for meteorological data. This function is similar to that of a typical communication satellite discussed subsequently Slide12: Communication satellites bring the world to you anywhere and any time….. Slide13: In 1945 Arthur C. Clarke first suggested the possibility of having world wide communication by having three geostationary ‘repeaters’ in orbit around the earth at a distance of 36,000 km above the equator. A repeater is simply a device that boosts the power of a communication signal after it has been reduced by traveling long distances. This summarizes the basic principles of communication satellites of today. Communication satellites can ‘see’ large parts of the earth at once because of their great height. Classes of Communication Satellites: Classes of Communication Satellites Geostationary: far away, stationary above equator at a fixed longitude.used for telephony, broadcast (e.g. DSTV), internet, ATM services etc Slide15: Global Position System(GPS) satellites are usually placed in swarms called constellations around the earth. So many are required because they are much closer to the earth’s surface and so see less. They are used for navigation this is achieved through the use of three different satellites visible at any one time by the GPS receiver. How do we escape gravity & place an object in orbit?: How do we escape gravity & place an object in orbit? If an object is fired fast enough it should escape the earths pull. This is done through the use of Rocket Launchers Multi-stage Rockets: Multi-stage Rockets Stage 1: Raises the payload e.g. a satellite to an elevation of about 50 miles. Stage 2: Satellite 100 miles and the third stage places it into the transfer orbit. Stage 3: The satellite is placed in its final geo-synchronous orbital slot by the AKM, a type of rocket used to move the satellite. Slide18: Physical Challenges In the Space Environment The space environment is very hostile. It has no air no cloud and no moisture; It is extremely cold (cold enough to instantly freeze human blood) and since there is no atmosphere extremely low pressure prevails. Against this backdrop, it is obvious that space craft have to be built to withstand very tough conditions so that they will last long and perform their duties well. it is not possible to have conventional power in such a remote place hence a satellite must carry its own power sources Finally, satellites drift away from their orbits due to several factors chief of which is the uneven attraction of the earth Slide19: Command and data handling subsystems. Power subsystem. This can include panels of solar cells that gather energy from the Sun. Telemetry Communications, Navigation system, on-board intelligence Thermal management equipment. Slide21: Space Debris: an emergent threat Slide22: Thank You!!!