What is a satellite?? A satellite is an object that moves around a larger object. Earth and Moon are called “Natural” satellites. “Man-made” satellites are machines made by scientists. These machines are launched into space and orbit Earth or another body in space.

Why are satellites important? Satellites fly high in the sky, So they can see large areas of earth at one time. Satellites also have a clear view of space. Before the invention of satellites, TV signals didn’t go very far. TV signals only travel in straight lines. So they would go off into space instead of following Earth’s curve.

Contd.. Sometimes they would be blocked by mountains or tall buildings. Phone calls to far away places were also a problem. It costs a lot and it is hard to set up telephone wires over long distances or underwater!! With satellites, TV signals and phone calls can be sent up to a satellite. The satellite can then send them back down to different spots on Earth.

What are the parts of a satellite?? Satellites come in many shapes and sizes. But most have at least two parts in common. They are 1)an antenna and 2)a power source. The antenna is used to send and receive information. The power source can be a solar panel or battery. Solar panels make power by turning sunlight into electricity. Many satellites carry cameras and scientific sensors. They may gather information about Earth’s land, air and water. Or they may collect data from the solar system and universe.

First satellite in space!! The Soviet Union was the first to launch a satellite into space. The satellite was launched in 1957 and was called “Sputnik 1”. NASA has launched many satellites into space. The first was “Explorer 1” in Explorer was America’s first man-made satellite.

The SPUTNIK 1

Incredible India India has launched 64 satellites (as of 25 February 2013) of many types. The first satellite was Aryabhata launched on It is a experimental/small satellite. The organization responsible for Indian satellites is the Indian Space Research organization (ISRO).

Cost Launching satellites is not cheap business!! They cost a lot of money(in fact Millions of Dollars) to design, construct, launch and to monitor. Running a satellite at a 36MHz bandwidth will cost over $1.5 million a year!!

How do satellites work?? Two stations on earth want to communicate through radio broadcast but are too far away to use conventional means. The two stations can use satellite as a relay station for their communication. One Earth Station sends a transmission to the satellite. This is called Uplink. The satellite Transponder converts the signal and sends it down to the second earth station. This is called a Downlink

Satellite orbits GEO(Geo stationary Earth Orbit) MEO(Medium Earth Orbit) LEO(Low Earth Orbit)

Geostationary Earth Orbit (GEO) These satellites are in orbit 35,863 km above the earth’s surface along the equator. Objects in Geostationary orbit revolve around the earth at the same speed as the earth rotates. This means GEO satellites remain in the same position relative to the surface of earth.

GEO (cont.) Advantages  A GEO satellite’s distance from earth gives it a large coverage area, almost a fourth of the earth’s surface.  GEO satellites have a 24 hour view of a particular area.  These factors make it ideal for satellite broadcast and other multipoint applications.

GEO (cont.) Disadvantages  A GEO satellite’s distance also cause it to have both a comparatively weak signal and a time delay in the signal, which is bad for point to point communication.  GEO satellites, centered above the equator, have difficulty broadcasting signals to near polar regions

A GEO Satellite

Medium Earth Orbit (MEO) A MEO satellite is in orbit somewhere between 8,000 km and 18,000 km above the earth’s surface. MEO satellites are similar to LEO satellites in functionality. MEO satellites are visible for much longer periods of time than LEO satellites, usually between 2 to 8 hours. MEO satellites have a larger coverage area than LEO satellites.

MEO (cont.) Advantage  A MEO satellite’s longer duration of visibility and wider footprint means fewer satellites are needed in a MEO network than a LEO network. Disadvantage  A MEO satellite’s distance gives it a longer time delay and weaker signal than a LEO satellite, though not as bad as a GEO satellite.

Low Earth Orbit (LEO) LEO satellites are much closer to the earth than GEO satellites, ranging from 500 to 1,500 km above the surface. LEO satellites don’t stay in fixed position relative to the surface, and are only visible for 15 to 20 minutes each pass. A network of LEO satellites is necessary for LEO satellites to be useful

LEO (cont.) Advantages  A LEO satellite’s proximity to earth compared to a GEO satellite gives it a better signal strength and less of a time delay, which makes it better for point to point communication.  A LEO satellite’s smaller area of coverage is less of a waste of bandwidth.

LEO (cont.) Disadvantages  A network of LEO satellites is needed, which can be costly  LEO satellites have to compensate for Doppler shifts cause by their relative movement.  Atmospheric drag effects LEO satellites, causing gradual orbital deterioration.

Types of Satellites Astronomical satellites are satellites used for observation of distant planets, galaxies, and other outer space objects. Communications satellites are artificial satellites stationed in space for the purposes of telecommunications using radio at microwave frequencies. Most communications satellites use geosynchronous orbits or near- geostationary orbits, although some recent systems use low Earth-orbiting satellites.

Earth observation satellites are satellites specifically designed to observe Earth from orbit, similar to reconnaissance satellites but intended for non-military uses such as environmental monitoring, meteorology, map making etc. Navigation satellites are satellites which use radio time signals transmitted to enable mobile receivers on the ground to determine their exact location. The relatively clear line of sight between the satellites and receivers on the ground, combined with ever-improving electronics, allows satellite navigation systems to measure location to accuracies on the order of a few meters in real time.

Reconnaissance satellites are Earth observation satellite or communications satellite deployed for military or intelligence applications. Space stations are man-made structures that are designed for human beings to live on in outer space. A space station is distinguished from other manned spacecraft by its lack of major propulsion or landing facilities - instead, other vehicles are used as transport to and from the station. Space stations are designed for medium-term living in orbit, for periods of weeks, months, or even years.

Weather satellites are satellites that primarily are used to monitor the weather and/or climate of the Earth. Drag-free satellites are satellites that offers an environment that is as isolated as possible from the forces of nature. A properly designed drag- free-satellite proof mass is uncoupled from the rest of the Universe to a remarkable degree. Miniaturized Satellites are satellites of unusually low weights and small sizes. New classifications are used to categorize these satellites: mini satellite ( kg), microsatellite (below 100kg), nanosatellite (below 10kg).

Applications of Sat. Comm. Radio and TV broadcasting Business radio and TV Telephony Thin route or trunk telephony Mobile satellite telephony LEO-based telephony GEO-based telephony Data, broadband and multimedia services IP over satellite for ISPs Corporate or institutional VSAT networks End-user services for home or small office Mobile data communications

Advantages of Satellites Higher bandwidths are available for use. Satellite to satellite communication is very precise. The coverage area of a satellite greatly exceeds that of a terrestrial communication. Transmission cost of a satellite is independent of the distance from the center of the coverage area.

Disadvantages of satellites Launching satellites into orbits is costly. Satellite bandwidth is gradually becoming used up. There is a larger propagation delay in satellite communication than in terrestrial communication.

By R.H.H.S.S.Prasad Y10ECE118083