Satellite Communications.

  • What is a Satellite?

A satellite is an object in space that orbits or circles around a bigger object. There are two kinds of satellites: natural (such as the moon orbiting the Earth) or artificial (such as the International Space Station orbiting the Earth).

There are dozens upon dozens of natural satellites in the solar system, with almost every planet having at least one moon. Saturn, for example, has at least 53 natural satellites, and between 2004 and 2017, it also had an artificial one, which explored the ringed planet and its moons.

Artificial satellites, however, did not become a reality until the mid-20th century. The first artificial satellite was Sputnik, a Russian beach-ball-size space probe that lifted off on Oct. 4, 1957. That act shocked much of the western world, as it was believed the Soviets did not have the capability to send satellites into space.

Orbital Objects

For half a century, humans have been putting satellites into orbit around Earth to serve a variety of functions. The Soviets launched the first, Sputnik 1, in October of 1957 just to prove they could. Four months later, the U.S. responded with Explorer 1.

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Since then, some 2,500 satellites have been sent aloft. These include Hubble and the ISS, the Russian Mir space station, the 27-satellite Global Positioning System, Iridium, GOES, Voyager, and hundreds of others that provide communications, broadcast television and radio signals, and help scientists predict weather, among many other purposes.

These man-made objects circle Earth in orbits that range from as near as 150 miles (240 kilometers) to 22,500 miles (36,200 kilometers) away. Satellites in low-Earth orbit, or LEO, stay within 500 miles (800 kilometers) and travel extremely fast—17,000 miles an hour (27,400 kilometers an hour) or more—to keep from being drawn back into Earth’s atmosphere. Most satellites around Earth are found in the LEO range.

Other objects are sent much farther into space and placed in what is called geosynchronous orbit. This allows the satellite to match the Earth’s rotation and “hover” over the same spot at all times. Weather and television satellites are generally in this category.

  • Satellite Communications.

A communications satellite is an artificial satellite that relays and amplifies radio telecommunications signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. Communications satellites are used for televisiontelephoneradiointernet, and military applications. There are about 2,000 communications satellites in Earth’s orbit, used by both private and government organizations.Many are in geostationary orbit 22,236 miles (35,785 km) above the equator, so that the satellite appears stationary at the same point in the sky, so the satellite dish antennas of ground stations can be aimed permanently at that spot and do not have to move to track it.

  • Parts of a satellite

Every usable artificial satellite — whether it’s a human or robotic one has a power system (which could be solar or nuclear, for example), a way to control its attitude, an antenna to transmit and receive information, and a payload to collect information (such as a camera or particle detector).

As will be seen below, however, not all artificial satellites are necessarily workable ones. Even a screw or a bit of paint is considered an “artificial” satellite, even though these are missing these parts.

  • ABSTRACT

Not so long ago, satellites were exotic, top-secret devices. They were used primarily in a military capacity, for activities such as navigation and espionage. Now they are an essential part of our daily lives. We see and recognize their use in weather reports, television transmission by DIRECTV and the DISH Network, in everyday telephone calls,in GPS(global positioning system)and by the media in transmitting their text and images to multiple printing sites for speed local distribution.

In the context of a worldwide communications network, satellite communications systems are very important. Satellite communications links add capacity to existing communications capabilities and provide additional alternate routings for communications traffic. Satellite links, as one of several kinds of long-distance links, interconnect switching centers located strategically around the world. They are part of the defense communication systems (DCS) network. One important aspect of the satellite communications network is that it continues in operation under conditions that sometimes render other methods of communications inoperable. Because of this, satellites make a significant contribution to improved reliability of Navy communications.

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