A satellite is any object that orbits around another, larger body. The Moon, for example, is a natural satellite of the Earth. An artificial satellite is a manufactured object that continuously orbits the Earth or some other body (moon, planets or sun) in space. Such satellites are used for gathering information about the other heavenly bodies. Most artificial satellites orbit the Earth. In this article, we shall discuss the artificial satellites in detail.
The British physicist, Sir Isaac Newton (1643-1723) in 1687 presented his theory of gravitation. An object when thrown up is pulled back to the earth. He formulated the equations governing the motion of bodies. He also calculated the speed required to launch a body into an orbit around the earth. It is about eight kilometres per second. The famous Russian physicist, Konstantin Tsiolkovsky (1857-1935) formulated the details of the space travel and rocket design towards the end of the 19th century. In his works, he described the future of satellites and even human travels into space. The works of Newton and Tsiolkovsky remained an academic exercise till the rocket technology was developed in the latter half of the 20th century.
On 4 October, 1957, the Soviet Union launched Sputnik 1, the first artificial satellite. It circled Earth once every 96 minutes and transmitted radio signals that could be received on Earth. On 3 November, 1957, the Soviets launched a second satellite, Sputnik 2. It carried a dog named Laika, the first animal to soar in space. The United States of America launched its first satellite, Explorer 1, on 31 January, 1958, and its second, Vanguard 1, on 17 March, 1958. This started the space age. Now there are thousands of satellites playing key roles in the communications industry; in military intelligence; and in the scientific study of both earth and outer space. Engineers have developed many different types of satellites designed to serve specific purposes. We shall briefly describe some of them below.
COMMUNICATION SATELLITES
The communications satellites serve as relay stations, receiving radio signals from one location and transmitting them to another. A communications satellite can relay several television programmes or thousands of telephone calls at once. Communications satellites are usually put in a high altitude, geosynchronous orbit (an orbit that keeps the satellite over the same spot above the earth) over a ground station. A ground station has a large dish antenna for transmitting and receiving radio signals. Countries and commercial organisations, such as television broadcasters and telephone companies, use these satellites continuously. If not for the telecommunication satellites, our life would have been very different without the numerous television channels and the affordable telephone networks.
NAVIGATION SATELLITES
Navigation satellites help in locating the positions of ships, aircraft, and even automobiles that are equipped with special radio receivers (global positions systems or GPS). A navigation satellite sends continuous radio signals to earth. These signals contain data that a special radio receiver on earth translates into information about the satellite’s position. The receiver further analyses the signal to find out how fast and in what direction the satellite is moving and how long the signal took to reach the receiver. From this data, the receiver can calculate its own location. Some navigation satellite systems use signals from several satellites at once to provide even more exact location information.
WEATHER SATELLITES
Weather satellites have special cameras and other equipment pointing to analyse the earth’s atmosphere. The data collected from these satellites is relayed to the meteorological centres on the earth. These centres use the data to make weather forecasts. These are particularly useful in predicting and tracking of storms.
MILITARY SATELLITES
Military satellites include weather, communications, navigation, and earth observing satellites used for military purposes. They are designed to observe (using very powerful cameras) the number and location of the ships, tanks, airplanes and military equipment. They can even detect the launch of missiles, the course of ships at sea, and the movement of military equipment on the ground. Thus the satellites used for spying gives an advantage to the countries, which have access to the satellite data.
SCIENTIFIC SATELLITES
Scientific satellites enable in studying the earth in detail. They enable in knowing the size and shape of the earth in great detail, mapping its magnetic field, dynamics of the oceans and the atmosphere. There are many satellites for studying the moon, planets, sun and the cosmos. Some satellites are also searching for life in outer space.
INDIAN SATELLITES
The Aryabhata spacecraft, named after the famous Indian mathematician and astronomer from the 5th century, was India’s first satellite. It was completely designed and fabricated in India by the Indian Space Research Organisation (ISRO, http://www.isro.org/). It was launched by a Soviet Kosmos-3M rocket from Kapustin Yar on 19 April 1975. The success of the launch was celebrated by issuing a postage stamp on 20 April 1975! Aryabhata spacecraft was also commemorated by stamping its imprint on the Indian two rupee bank note from 1976 to 1977. ISRO’s vision is to harness space technology for national development, while pursuing space science research and planetary exploration. India has launched numerous satellites.
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Chandrayaan-1 was India’s first mission to the Moon. It was launched on 22 October 2008 from Satish Dhawan Space Centre, Sriharikota. Chandrayaan-1 became the first lunar mission to discover existence of water on the Moon. Mars Orbiter Mission known as Mangalayaan is India’s first interplanetary mission to planet Mars with an orbiter craft designed to orbit Mars in an elliptical orbit. Mangalayaan was launched into Earth orbit on 5 November 2013 by ISRO and entered Mars orbit on 24 September 2014. Only the US, Russia and Europe have previously sent missions to Mars, and India has succeeded on its very first attempt!
Since the dawn of space age in 1957, about 6,600 satellites have been launched. The latest estimates are that 3,600 remain in orbit, of which about 1,000 are operational. The rest have lived out their useful lives and are part of the space debris. Over the last six decades the artificial satellites have changed our way of life in many ways. It is difficult to predict the influence of satellites on our lives in times to come.
[HAJIRA KHAN studies at Indian School Salalah and SAMEEN AHMED KHAN teaches at Engineering Department, Salalah College of Technology, Salalah, Oman. [email protected]]