Communications satellites are used to send and receive radio signals for television, phone or internet communications. Large concave reflectors called satellite dishes are normally used to send and receive these signals. All signals for television, telephone or internet are converted into radio signals and then sent towards the satellite using a transmitting satellite dish.
Most satellite dishes are designed to only receive satellite signals, but some are used to send signals to satellites as well. A satellite dish works in the same way as the reflector for a torch or car headlights.
A signal is produced or reflected from a focal point. This signal then reflects off the large part of the satellite dish and travels towards the satellite. At the satellite, the signal reflects off another curved reflector towards a focal point where the signal is received.
The signal is then amplified and sent back towards Earth using a different frequency. The shape of a satellite dish is called a parabola. Home satellite dishes normally only contain a small section of the side part of the parabolic shape. The signal is reflected towards the receiver, which contains a small metal bar that acts as the antenna. For television reception, the signal is then amplified and sent to the television decoder. Radio waves are used to carry satellite signals.
This means that a signal sent to a satellite 38, km away takes 0. If several satellite links are used, the delay for a signal to be received from the other side of the world is a quarter of a second greater for each satellite link used. This time delay can be seen when a television interviewer asks a question to a person on the other side of the world.
There is often a short delay between the question asked and the answer given. Only one satellite is needed to transmit television signals to a whole country or other large region of the Earth. The signals sent from a satellite can be shaped to match any coverage footprint required.
The Iridium system has 66 satellites. It is also possible today to provide discontinuous coverage using a low-earth-orbit satellite that can store data received while passing over one part of earth and transmitting it later while passing over another part. At the time, it was fitted 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.
That said, it was not placed in orbit to send data from one point on earth to another. The first satellite to relay communications was in fact Pioneer 1, an intended lunar probe. The spacecraft made it halfway to the moon, and flew high enough to carry out the proof of concept relay of telemetry across the world: first from Cape Canaveral to Manchester, England; then from Hawaii to Cape Canaveral; and finally, across the world from Hawaii to Manchester.
They are the first and historically most important use of communications satellites. The fixed Public Switched Telephone Network carries telephone calls from landline phones to an earth station, from where they are transmitted to a geostationary satellite.
The downlink follows an analogous path. With significant improvements in submarine communications cables through the use of fiber-optics, satellites are no longer being used for fixed telephony on the same scale.
Remote places such as Ascension Island, Saint Helena, Diego Garcia, and Easter Island have no submarine cables in service, so those areas need satellite telephones. Satellite communication is also needed in continents and countries where landline telecommunications are rare to nonexistent - say, in Antarctica, Greenland large regions of South America, Africa, Canada, China, Russia, and Australia.
Other land use for satellite phones include ships at sea, rigs at sea, back up for hospitals, military and recreation. Typically, satellite phone systems function through a local telephone system in an isolated area with a link to the telephone system in a main land area. There are also services that will send a radio signal to a telephone system.
In this example, almost any type of satellite can be used. Satellite phones reach out directly to a constellation of either geostationary or low-earth-orbit satellites. Calls are then forwarded to a satellite teleport connected to the Public Switched Telephone Network. The signals are received through an outdoor parabolic antenna called a satellite dish and a low-noise block downconverter.
A satellite receiver - either an external set-top box, or a built-in television tuner - decodes the desired television programme for viewing on a television set. Satellite television offers a wide range of channels and services. It is the only television available in many remote areas that do not have terrestrial television or cable television service. Modern systems signals are passed on from a communications satellite on the Ku band frequencies 12—18 GHz that need only a small dish less than a meter in diameter.
Also unlike early systems that used analog signals, modern ones use digital signals which allow transmission of the modern television standard high-definition television, thanks to the much improved spectral efficiency of digital broadcasting. Different receivers are required for the two types. Some transmissions and channels are unencrypted and thus free-to-air or free-to-view.
Other channels are transmitted with encryption pay television , needing the viewer to subscribe and pay a monthly fee to receive the programming. Satellite TV consumption now has a lot less takers due to the cord-cutting trend where people are preferring to watch internet based streaming television. A satellite radio or subscription radio SR is basically a digital radio signal that is relayed by a communications satellite and this typically covers a wider geographical range than terrestrial radio signals.
Satellite radio provides audio broadcast services in some countries, among them is the US. Mobile services, like SiriusXM, and Worldspace, let listeners travel across the continent and tune in to the same audio programming anywhere. In all instances, the antenna should have a clear view to the satellites. In places that have tall buildings, bridges, or even parking garages obscuring the signal, repeaters can be used to make the signal available to listeners.
Amateur radio operators make use of amateur satellites, that have been created specifically for amateur radio traffic. Most of these satellites function as spaceborne repeaters, and are generally used by amateurs equipped with UHF or VHF radio equipment and highly directional antennas like Yagis or dish antennas.
Due to launch costs, most amateur satellites are launched into low earth orbits, and are designed to deal with only a few brief contacts at a given time. Satellite Internet access refers to Internet access made possible through communications satellites.
After the s, satellite communication technology has been used as a means to connect to the Internet using broadband data connections. This is particularly useful for people in remote areas who cannot avail a broadband connection. Communications satellites are also used for military communications applications, such as Global Command and Control Systems.
Since the launch of the first satellite Sputnik 1, around 8, satellites from more than 40 countries have been launched. According to a estimate, 5, are in orbit. Some large space stations have in fact been launched in parts and assembled in orbit. It is important to note that out of the 5, satellites in orbit, only 1, were operational in , while the rest have now become space debris.
Indeed, the space pollution caused by this space debris is a big problem today. So what is space debris? Space debris refers to the natural debris found in the solar system, so it includes asteroids, comets, and meteoroids. But it is no longer limited just to these bodies. Since the beginning of the NASA Orbital Debris Program, the term also refers to space waste or space garbage that is generated from the mass of defunct, artificially created objects in space, especially in the earth orbit.
These include old satellites and spent rocket stages and the fragments from their disintegration and collisions. As of December , five satellite collisions have generated space debris. Space debris is also known as space trash, space litter, space junk or orbital debris. Today, several steps are being taken to deal with such debris.
The U. In , the International Organization for Standardization ISO began preparing an international standard for space-debris mitigation. Germany and France have posted bonds to safeguard property from debris damage. Another approach to debris mitigation is designing the mission architecture so as to always leave the rocket second-stage in an elliptical geocentric orbit with a low-perigee, thus ensuring rapid orbital decay and avoiding long-term orbital debris from spent rocket bodies.
External removal of space debris has not seen many takers primarily because it has been found to be not cost effective. This mission aims to test the efficiency of several Active Debris Removal ADR technologies on mock targets in low earth orbit.
It will do so by carrying out several planned experiments and the platform is accordingly fitted with a net, a harpoon, a laser ranging instrument, a dragsail, and two CubeSats miniature research satellites. This blog is presented to you by YoungWonks. The leading coding program for kids and teens.
0コメント