What is a satellite | How To Work Satellites?

satellite doesn’t necessarily have to be a tin can spinning through space. The word “satellite” is more general than that: it means a smaller, space-based object moving in a loop (an orbit) around a larger object. The Moon is a natural satellite of Earth, for example, because gravity locks it in orbit

around our planet. The tin cans we think of as satellites are actually artificial (human-built) satellites that move in precisely calculated paths, circular or elliptical (oval), at various distances from Earth, usually well outside its atmosphere.

To understand why satellites move this way, we must revisit our friend Newton. Newton proposed that a force – gravity – exists between any two objects in the universe. If it weren’t for this force, a satellite in motion near a planet would continue in motion at the same speed and in the same direction – a straight line.

What do they do?

Communications satellites are “space mirrors” that can help us bounce radio, TV, Internet data, and other kinds of information from one side of Earth to the other.

Satellite orbits:

One of the most surprising things about satellites is the very different paths they follow at very different heights above Earth. Left to its own devices, a satellite fired into space might fall back to Earth just like a stone tossed into the air. To stop that happening, satellites have to keep moving all the time so, even though the force of gravity is pulling on them, they never actually crash back to Earth. Although there are many different types of satellite orbits, they come in three basic varieties, low, medium, and high—which are short, medium, and long distances above Earth, respectively.

High-Earth orbits:

Many satellites have orbits at a carefully chosen distance of about 36,000 km (22,000 miles) from the surface. This “magic” position ensures they take exactly one day to orbit Earth and always return to the same position above it, at the same time of day. A high-Earth orbit like this is called geosynchronous (because it’s synchronized with Earth’s rotation) or geostationary (if the satellite stays over the same point on Earth all the time). Communications satellites—our “space mirrors”—are usually parked in geostationary orbits so their signals always reach the satellite dishes pointing up at them. Weather satellites often use geostationary orbits because they need to keep gathering cloud or rainfall images from the same broad part of Earth from hour to hour and day to day (unlike LEO scientific satellites, which gather data from many different places over a relatively short period of time, geostationary weather satellites gather their data from a smaller area over a longer period of time).

Medium-earth orbits:

The higher up a satellite is, the longer it spends over any one part of Earth. GPS Navistar satellites are in MEO orbits roughly 20,000 km (12,000 miles) above our heads and take 12 hours to “loop” the planet. Their orbits are semi-synchronous, which means that, while they’re not always exactly in the same place above our heads, they pass above the same points on the equator at the same times each day.  It’s just the same as jet planes flying over your head: the slower they move through the sky, the higher up them are. A medium-Earth orbit (MEO) is about 10 times higher up than a LEO.

Low-Earth orbits:

Scientific satellites tend to be quite close to Earth—often just a few hundred kilometers up—and follow an almost circular path called a low-Earth orbit (LEO). Some follow what’s called a polar orbit, passing over both the North and South poles in a “loop” taking just over an hour and a half to complete. Since they have to be moving very fast to overcome Earth’s gravity, and they have a relatively small orbit, they cover large areas of the planet quite quickly and never stay over one part of Earth for more than a few minutes.

Communications satellites:

Allow telephone and data conversations to be relayed through the satellite. Typical communications satellites include Telstar and Intelsat. The most important feature of a communications satellite is the transponder — a radio that receives a conversation at one frequency and then amplifies it and retransmits it back to Earth on another frequency. A satellite normally contains hundreds or thousands of transponders. Communications satellites are usually geosynchronous.

Uplinks and downlinks:

If you want to send something like a TV broadcast from one side of Earth to the other, there are three stages involved. First, there’s the uplink, where data is beamed up to the satellite from a ground station on Earth. Next, the satellite processes the data using a number of onboard transponders (radio receivers, amplifiers, and transmitters). These boost the incoming signals and change their frequency, so incoming signals don’t get confused with outgoing ones. Different transponders in the same satellite are used to handle different TV stations carried on different frequencies. Finally, there’s the downlink, where data is sent back down to another ground station elsewhere on Earth. Although there’s usually just a single uplink, there may be millions of downlinks, for example, if many people are receiving the same satellite TV signal at once.

Satellites are like any other vehicle inasmuch as they have two main parts: the generic vehicle itself and the specific thing it carries to do its unique job. The “vehicle” part of a satellite is called the bus, and it includes the outer case, the solar panels and batteries that provide power, telemetry rocket thrusters to keep it in position, and reflective materials or other systems to protect it from solar radiation and dissipate heat.

About the Author

Rabin

I am a self taught white hat hacker and a B.sc in Hardware & Networking graduate from India. I am running a Blog for my community where I technical things in “English” which makes this experience even more interesting.

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