Satellites Essay, Research Paper

Satellites

A satellite is any object that orbits or revolves around another object. For example, the Moon is a satellite of Earth, and Earth is a satellite of the Sun. The payload is all the equipment a satellite needs to do its job. This can include antennas, cameras, radar, and electronics. The payload is different for every satellite. For example, the payload for a weather satellite includes cameras to take pictures of cloud formations, while the payload for a communications satellite includes large antennas to transmit TV or telephone signals to Earth. The bus is the part of the satellite that carries the payload and all its equipment into space. It holds all the satellite’s parts together and provides electrical power computers, and propulsion to the spacecraft. The bus also contains equipment that allows the satellite to communicate with Earth. Communications satellites act as relay stations in space. People use them to bounce messages from one part of the world to another. These messages can be telephone calls, TV pictures, or even Internet connections like the one you’re using now.

Communications satellites are in geosynchronous orbit (from geo = Earth + synchronous =moving at the same rate). That means that the satellite always stays over one spot on Earth. The area on Earth that it can “see” is called the satellite’s “footprint.” Here is one footprint that covers all of Africa. A person in Africa can use this satellite to communicate with anyone else in Africa. We can also use satellites as a relay system to send signals anywhere on Earth. Here you can see the overlapping footprints of four different satellites. If you wanted to send a signal from Africa to Southeast Asia, you could bounce, or relay, the signal using more than one satellite. A satellite is a complex machine. All satellites are made up of several sub-systems that work together as one large system to help the satellite achieve its mission. Command and data, pointing control, communications, power supply, mission payload, and thermal control are the names of the several sub systems.

The parts of a satellite are transmitter/ receiver, high gain antennas, image sensor, flight computer, digital camera, omni antennas, I/O processor, reaction wheels, star trackers, bus structures, battery, thermal blanket, and solar arrays. These parts make the satellite work. When a satellite circles close to Earth we say its in Low Earth Orbit (LEO). Satellites in LEO are just 200 – 500 miles (320 – 800 kilometers) high. Because they orbit so close to Earth, they must travel very fast so gravity won’t pull them back into the atmosphere. Satellites in LEO speed along at 17,000 miles per hour (27,359kilometers per hour)! They can circle Earth in about 90 minutes. A Low Earth Orbit is useful because its nearness to Earth gives it spectacular views. The crew in a Space Shuttle traveling in low earth orbit took this picture. Satellites that observe our planet, like Remote Sensing and Weather satellites, often travel in LEOs because from this height they can capture very detailed images of Earth’s surface.

A Polar orbit is a particular type of Low Earth Orbit. The only difference is that a satellite in polar orbit travels a north-south direction, rather than the more common east-west direction. Polar orbits are useful for viewing the planet’s surface. As a satellite orbits in a north-south direction, Earth spins beneath it in an east-west direction. As a result, a satellite in polar orbit can eventually scan the entire surface. It?s like pealing an orange in one piece. Around and around, one strip at a time, and finally you’ve got it all. For this reason, satellites that monitor the global environment, like remote sensing satellites and certain weather satellites, are almost always in polar orbit. No other orbit gives such thorough coverage of Earth.

A satellite in geosychonous equatorial orbit (GEO) is located directly above the equator, exactly 22,300 miles out in space. At that distance, it takes the satellite a full 24 hours to circle the planet. Since it takes Earth 24 hours to spin on in its axis, the satellite and Earth move together. So, a satellite in GEO always stays directly over the same spot on Earth. (A geosynchronous orbit can also be called a GeoSTATIONARY Orbit.) A satellite in elliptical orbit follows an oval-shaped path. One part of the orbit is closest to the center of Earth (perigee) and the other part is farthest away (apogee). A satellite in this orbit takes about 12 hours to circle the planet. Like polar orbits, elliptical orbits move in a north-south direction. Well that?s all about satellites that are in space and their functions.

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