A satellite is a small thing orbiting or circling a larger thing. The complete path it follows is called an orbit. The moon is a example of a natural satellite of the earth. Manmade, or artificial satellites are placed into orbit by rockets or space shuttles.
After World War II, the former Soviet Union successfully launched Sputnik I, the first artificial satellite in 1951, into space. In 1958, the United States launched its first artificial satellite Telstar I into orbit. Since then, many more satellites were made by different countries and launched into space.
How can they help us daily / what is the purpose with satellites
It has been helping scientists find answers to the unknown, and assisting tourists finding their way when they are lost. Today, satellites have become so widely used that some of them have become available to civilians around the globe with over 150 countries funding them. With over 2200 operational satellites orbiting the Earth. If we wish to understand why artificial satellites are so useful, we have to understand what each type of satellites are doing starting with Global Positioning system (GPS), Reconnaissance Satellites, and finally Telecommunications Satellites.
The Global Positioning System provides users with accurate information about their latitude, longitude, velocity and altitude, as well as the time, anywhere in the world. The GPS was launch in 1973 by Navstar in the United States and then followed by the Soviet Union with their own GPS. Both GPS systems are free to use by anyone around the world and offers great benefits to the military, companies, and you and me.
There are various types of Reconnaissance Satellites. There are the basic models which are used for photography; then there are more sophisticated models called “spy satellites” which are capable of capturing motion pictures from Earth’s surface, and finally there are the media satellites equipped with special sensors such as heat, infrared and ultra-violet sensors. Each type of satellite has its own set of equipment, and benefits humankind in many ways. The most basic models for instance, helps scientists learn what happened billions of years ago to our planet, how our solar system was born, the depth and activity of volcanoes around the world, and much more. Astronomers who also use the basic models can take pictures of Earth, nearby planets and faraway solar systems to study them and be able to determine facts such as, if life is possible to exist anywhere else in the galaxy, what are black holes and to discover new planets galaxies far far away.
The most common satellites in space are the Telecommunications Satellites. Capable of transferring massive amounts of data at a time, they are without a doubt the most widely employed satellites in the world. Similarly to GPS, Telecommunication Satellites are practically only used by the military, commercial companies and civilian residents. In commerce, communication is just as important and can benefit the entire world. The Internet is a great example of how satellites are able relay hundreds of countries in one single network and whether you are researching information on Egypt, online shopping in a Japanese site, or looking for television programs, it is the satellites which are doing all the hard work of transferring the information from one place to another with short delay.
This covers just a few of the thousands of different things that satellites have to offer in our everyday life.
How do they orbit?
An orbit is a regular, repeating path that one object in space takes around another one. An object in an orbit is called a satellite. A satellite can be natural, like the Earth or the Moon. It can also be man-made, like the Space Shuttle or a man made satellite.
Orbits are elliptical in shape, this means they are similar to an oval. For the planets, the orbits are almost round. The orbits of comets have a different shape. They are highly eccentric or “squashed.” Satellites that orbit the Earth are not always the same distance from the Earth. Sometimes they are closer, and at other times they are farther away. The closest point a satellite comes to the Earth is called its perigee. The farthest point is the apogee. The time it takes a satellite to make one full orbit is called its period. The slope is the angle the orbital plane makes when compared with the Earth’s equator.
Isaac Newton’s First Law of Motion sounds like this any given object there is in motion will stay in motion unless something pushes or pulls on it. Without gravity an Earth-orbiting satellite would go off into space along a straight line. With gravity it is pulled back toward the Earth. There is a constant tug-of-war between the satellites tendency to move in a straight line, or momentum, and the tug of gravity pulling it back.
An object’s momentum and gravity have to be balanced for an orbit to happen. If the forward momentum of one object is too great, it will speed past the other one and not enter into orbit. If momentum is too small, the object will be pulled into the other one and crash. When these forces are balanced, the object is always falling into the planet, but because it’s moving sideways fast enough, it never hits the planet.
Escape velocity is the speed an object must go to break free from a planet?s gravity and enter into orbit. Escape velocity depends on the mass of the planet. Each planet has a different escape velocity. The object?s distance from the planet?s center is also important. The escape velocity from the Earth is about 11.3 kilometers pr second.
Earth Orbit (LEO) is restricted to the first 65 to 130 kilometer of space. LEO is the easiest orbit to get to and stay in. This is where the Shuttle and ISS conduct their operations. One complete orbit in LEO takes about 90 minutes.
Satellites that seem to be at the location on Earth, are in Geosynchronous(geostationary) Earth Orbit (GEO). These satellites orbit about 14,375 kilometer above the equator and complete one round of the Earth precisely every 24 hours. Satellites headed for GEO first go to an elliptical orbit with an apogee about 14,375 kilometer. Firing the rocket engines at apogee then makes the orbit round.
Any satellite with an orbital path going over or near the poles maintains a polar orbit. Polar orbits are usually in low Earth orbit. They remain in place while the Earth passes under. This means that eventually, the entire Earth’s surface passes under a satellite in polar orbit.
Satellite Power Sources
Early communications satellites were very limited by the lack of suitable power sources. The only source of power available within early weight restrictions was a very inefficient panel of solar cells without battery backup. A major disadvantage of this type of power source is that the satellite has no power when it is in ECLIPSE (not in view of the sun). For continuous communications, this outage is unacceptable.
A combination of solar cells and storage batteries is a better prime power source. This is a practical choice, even though the result is far from an ideal power source. Only about ten percent of the energy of the sunlight that strikes the solar cells is converted to electrical power. This low rate is sometimes decreased even further.
Early satellites had over 8,500 solar cells mounted on the surface of the satellite, which supplied about 42 watts of power. No battery backup was provided in these satellites.
Nowadays satellites have about 32,000 solar cells installed on the surface of the satellite, and they supply about 520 watts. A battery is used for backup power during eclipses (not in view of the sun).
Nuclear power sources have been used in space for special purposes, but their use stops there. Technology has not progressed sufficiently for nuclear power sources to be used as a power source.
Satellite orientation in space is important for continuous solar cell and antenna orientation. Since the primary source of power in most satellites is from solar cells, a maximum number of the solar cells must be exposed to the sun at all times. The satellite antenna must also be pointed at the appropriate earth terminals. Our communications satellites use what is termed spin stabilization to meet these important requirements.
Once the system is in motion, spin stabilization requires actually no extra energy. A spin-stabilized satellite is usually constructed like a flywheel. After reaching its orbit, the jets are pulsed to start the satellite spinning. The satellite spin axis is orientated to the axis of the earth by means of small axial jets. Velocity jets, are used to place the satellite in orbit position and provide velocity correction.
Solar cells are installed around the outside surface of the satellite. This gives a large number of solar cells exposed to the sun 24 hours a day.
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