Satellite communications

List of orbits Various earth orbits to scale; cyan represents low earth orbit, yellow represents medium earth orbit, the black dashed line represents geosynchronous orbit, the green dash-dot line the orbit of Global Positioning System GPS satellites, and the red dotted line the orbit of the International Space Station ISS. The first satellite, Sputnik 1was put into orbit around Earth and was therefore in geocentric orbit. By far this is the most common type of orbit with approximately 1, [20] artificial satellites orbiting the Earth.

Satellite communications

History[ edit ] The concept of the geostationary communications satellite was first proposed by Arthur C.

Clarkealong with Vahid K. Sanadi building on work by Konstantin Tsiolkovsky. Its objective was to develop a secure and reliable method of wireless communication by using the Moon as a passive reflector and natural communications satellite.

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The first artificial Earth satellite was Sputnik 1. Put into orbit by the Soviet Union on October 4,it was equipped with an on-board radio - transmitter that worked on two frequencies: Sputnik 1 was launched as a major step in the exploration of space and rocket development.

However, it was not placed in orbit for the purpose of sending data from one point on earth to another. The first artificial satellite used solely to further advances in global communications was a balloon named Echo 1.

The idea behind a communications satellite is simple: Send data up into space and beam it back down to another spot on the globe.

Communications satellite - Wikipedia

Echo 1 accomplished this by essentially serving as an enormous mirror, 10 stories tall, that could be used to reflect communications signals. The first American satellite to relay communications was Project SCORE inwhich used a tape recorder to store and forward voice messages.

It was used to send a Christmas greeting to the world from U. There are two major classes of communications satellites, passive and active. Passive satellites only reflect the signal coming from the source, toward the direction of the receiver. With passive satellites, the reflected signal is not amplified at the satellite, and only a very small amount of the transmitted energy actually reaches the receiver.

Since the satellite is so far above Earth, the radio signal is attenuated due to free-space path lossso the signal received on Earth is very, very weak.

Active satellites, on the other hand, amplify the received signal before retransmitting it to the receiver on the ground.

Telstar was the second active, direct relay communications satellite. Relay 1 was launched on December 13,and it became the first satellite to transmit across the Pacific Ocean on November 22, Syncom 2 was the first communications satellite in a geosynchronous orbit.

It revolved around the earth once per day at constant speed, but because it still had north-south motion, special equipment was needed to track it. Its successor, Syncom 3 was the first geostationary communications satellite. Syncom 3 obtained a geosynchronous orbit, without a north-south motion, making it appear from the ground as a stationary object in the sky.

Beginning with the Mars Exploration Roverslanders on the surface of Mars have used orbiting spacecraft as communications satellites for relaying their data to Earth.

The landers use UHF transmitters to send their data to the orbiters, which then relay the data to Earth using either X band or Ka band frequencies.

Satellite communications

These higher frequencies, along with more powerful transmitters and larger antennas, permit the orbiters to send the data much faster than the landers could manage transmitting directly to Earth, which conserves valuable time on the NASA Deep Space Network. This orbit has the special characteristic that the apparent position of the satellite in the sky when viewed by a ground observer does not change, the satellite appears to "stand still" in the sky.

The advantage of this orbit is that ground antennas do not have to track the satellite across the sky, they can be fixed to point at the location in the sky the satellite appears. As satellites in MEO and LEO orbit the Earth faster, they do not remain visible in the sky to a fixed point on Earth continually like a geostationary satellite, but appear to a ground observer to cross the sky and "set" when they go behind the Earth.

Communications satellite - Wikipedia Make sure you can communicate if the need arises. This offer includes an Iridium satellite phone with a minute voucher available via select Iridium partners through November 1,

Therefore, to provide continuous communications capability with these lower orbits requires a larger number of satellites, so one will always be in the sky for transmission of communication signals. However, due to their relatively small distance to the Earth their signals are stronger.L3 Global Communications Solutions Incorporated, Victor, New York, was awarded an $8,, undefinitized contract action for sustainment of the Army's existing combat services support, for very small aperture terminal transmission systems and satellite communications terminals.

The Army Contract Command, Rock Island Arsenal, . Mobile satellite systems help connect remote regions, vehicles, ships, people and aircraft to other parts of the world and/or other mobile or stationary communications units, in addition to serving as navigation systems.

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.

How do satellites communicate? | NASA

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Satellite communications basics tutorial - an overview, tutorial and information about the basics of satellite communications and the various types of satellite communication systems that are in use today.

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Satellite communications
Satellite Communications: