How many communications satellites are there




















The communication satellites are owned by a variety of private companies including France Telecom and Stellat. These satellites area also owned by several governments. The purpose for having communication satellites in space, is by providing telecommunication throughout the world. Communication satellites are mostly used for mobile phone signals, weather tracking, and broadcasting television programs.

There are nine types of artificial satellites. Here is the list: Astronomical satellites, Biosatellites satellites, Communication satellites, Miniaturized Satellites, Navigational satellites, Reconnaissance satellites, Earth observation satellites, Space stations, and Weather satellites.

These are the different artificial Satellite orbiting the Planet Earth. The planet Earth upon which we live has precisely one natural satellite, which is known as the moon, or Luna, and it has a great many artificial satellites, including the International Space Station, communication satellites, surveillance satellites, global positioning satellites, etc. Yes, they are. The ionosphere. There are also the satellites of the Global Positioning System and military satellites.

For communication satellites the range is much higher than that of communication relay. Communication Satellite can cover up to several thousands of kilometers. For communication relay, the uplink and the downlink frequency is the same. But for communication satellites the uplink and the downlink frequencies are different in order to avoid interference.

The earth has one natural satellite A satellite of earth that is not man made is the moon. There are many satellites that are man made that orbit the earth. These satellites are used for communication between Internet and television viewing.

Telecommunication satellites. Log in. Satellite Television. Broadband Internet. Artificial Satellites. The Moon. See Answer. Best Answer. Finally, many high Earth orbiting satellites monitor solar activity.

At the Lagrange points, the pull of gravity from the Earth cancels out the pull of gravity from the Sun. Anything placed at these points will feel equally pulled toward the Earth and the Sun and will revolve with the Earth around the Sun. Of the five Lagrange points in the Sun-Earth system, only the last two, called L4 and L5, are stable. A satellite at the other three points is like a ball balanced at the peak of a steep hill: any slight perturbation will push the satellite out of the Lagrange point like the ball rolling down the hill.

Satellites at these three points need constant adjustments to stay balanced and in place. Satellites at the last two Lagrange points are more like a ball in a bowl: even if perturbed, they return to the Lagrange point. The first Lagrange point is located between the Earth and the Sun, giving satellites at this point a constant view of the Sun. The second Lagrange point is about the same distance from the Earth, but is located behind the Earth.

Earth is always between the second Lagrange point and the Sun. Since the Sun and Earth are in a single line, satellites at this location only need one heat shield to block heat and light from the Sun and Earth. The third Lagrange point is opposite the Earth on the other side of the Sun so that the Sun is always between it and Earth.

A satellite in this position would not be able to communicate with Earth. Closer to the Earth, satellites in a medium Earth orbit move more quickly. Two medium Earth orbits are notable: the semi-synchronous orbit and the Molniya orbit. The semi-synchronous orbit is a near-circular orbit low eccentricity 26, kilometers from the center of the Earth about 20, kilometers above the surface. A satellite at this height takes 12 hours to complete an orbit. As the satellite moves, the Earth rotates underneath it.

In hours, the satellite crosses over the same two spots on the equator every day. This orbit is consistent and highly predictable. The second common medium Earth orbit is the Molniya orbit. Invented by the Russians, the Molniya orbit works well for observing high latitudes. The Molniya orbit offers a useful alternative. The Molniya orbit is highly eccentric: the satellite moves in an extreme ellipse with the Earth close to one edge.

As it moves away, its speed slows, so it spends more time at the top of its orbit farthest from the Earth. A satellite in a Molniya orbit takes 12 hours to complete its orbit, but it spends about two-thirds of that time over one hemisphere. Like a semi-synchronous orbit, a satellite in the Molniya orbit passes over the same path every 24 hours. This type of orbit is useful for communications in the far north or south.

Most scientific satellites and many weather satellites are in a nearly circular, low Earth orbit. Therefore, it has a relatively low inclination 35 degrees , staying near the equator. In this highly inclined orbit, the satellite moves around the Earth from pole to pole, taking about 99 minutes to complete an orbit.

During one half of the orbit, the satellite views the daytime side of the Earth. At the pole, satellite crosses over to the nighttime side of Earth. As the satellites orbit, the Earth turns underneath. By the time the satellite crosses back into daylight, it is over the region adjacent to the area seen in its last orbit. In a hour period, polar orbiting satellites will view most of the Earth twice: once in daylight and once in darkness. Just as the geosynchronous satellites have a sweet spot over the equator that lets them stay over one spot on Earth, the polar-orbiting satellites have a sweet spot that allows them to stay in one time.

This orbit is a Sun-synchronous orbit, which means that whenever and wherever the satellite crosses the equator, the local solar time on the ground is always the same. When the satellite comes around the Earth in its next overpass about 99 minutes later, it crosses over the equator in Ecuador or Colombia at about local time.

The Sun-synchronous orbit is necessary for science because it keeps the angle of sunlight on the surface of the Earth as consistent as possible, though the angle will change from season to season. This consistency means that scientists can compare images from the same season over several years without worrying too much about extreme changes in shadows and lighting, which can create illusions of change.

Without a Sun-synchronous orbit, it would be very difficult to track change over time. It would be impossible to collect the kind of consistent information required to study climate change. The path that a satellite has to travel to stay in a Sun-synchronous orbit is very narrow. If a satellite is at a height of kilometers, it must have an orbital inclination of 96 degrees to maintain a Sun-synchronous orbit.

Any deviation in height or inclination will take the satellite out of a Sun-synchronous orbit. The amount of energy required to launch a satellite into orbit depends on the location of the launch site and how high and how inclined the orbit is. Satellites in high Earth orbit require the most energy to reach their destination.

Satellites in a highly inclined orbit, such as a polar orbit, take more energy than a satellite that circles the Earth over the equator. Click here for our Site Map. Whalen In years, when humankind looks back at the dawn of space travel, Apollo's landing on the Moon in may be the only event remembered.

At the same time, however, Lyndon B. Johnson, himself an avid promoter of the space program, felt that reconnaissance satellites alone justified every penny spent on space. Weather forecasting has undergone a revolution because of the availability of pictures from geostationary meteorological satellites--pictures we see every day on television. All of these are important aspects of the space age, but satellite communications has probably had more effect than any of the rest on the average person.

Satellite communications is also the only truly commercial space technology- -generating billions of dollars annually in sales of products and services. Clarke, wrote a short article in Wireless World that described the use of manned satellites in hour orbits high above the world's land masses to distribute television programs.

Perhaps the first person to carefully evaluate the various technical options in satellite communications and evaluate the financial prospects was John R. After the launch of Sputnik I, many considered the benefits, profits, and prestige associated with satellite communications. Because of Congressional fears of "duplication," NASA confined itself to experiments with "mirrors" or "passive" communications satellites ECHO , while the Department of Defense was responsible for "repeater" or "active" satellites which amplify the received signal at the satellite--providing much higher quality communications.

The U. The military program, ADVENT, was cancelled a year later due to complexity of the spacecraft, delay in launcher availability, and cost over-runs. COMSAT's initial capitalization of million dollars was considered sufficient to build a system of dozens of medium-orbit satellites.

They chose the hour-orbit geosynchronous satellite offered by Hughes Aircraft Company for their first two systems and a TRW geosynchronous satellite for their third system.

Global satellite communications had begun. These had included televising parts of the Tokyo Olympics. Further negotiations in and resulted in a new international organization, which would ultimately assume ownership of the satellites and responsibility for management of the global system. From a few hundred telephone circuits and a handful of members in , INTELSAT has grown to a present-day system with more members than the United Nations and the capability of providing hudreds of thousands of telephone circuits.

If the effects of inflation are included, this is a tremendous decrease! RCA promptly leased circuits on the Canadian satellite until they could launch their own satellite.

The first U. These satellites were used for voice and data, but very quickly television became a major user. By the end of there were transponders available over the U. Very quickly the "movie channels" and "super stations" were available to most Americans. The dramatic growth in cable TV would not have been possible without an inexpensive method of distributing video. Television still dominates domestic satellite communications, but data has grown tremendously with the advent of very small aperture terminals VSATs.

It was three-axis stabilized rather than spinning. It had an antenna that directed its radio energy at the earth. It was rather sophisticated and heavy.



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