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Wednesday, 8 July 2015

Introduction to Satellites

Today, on Embrace Space, we are going to examine satellites! This cursory introduction will help familiarize you with what is necessary for a satellite to function. If you're already familiar, feel free to come back later when these posts become more technical and focus on interesting new developments in the industry! 

A simple definition is that a satellite is "any object orbiting a celestial body". This broad definition could include the Moon (orbiting the Earth), the International Space Station (an artificial satellite, orbiting the Earth), or the Earth itself (as it orbits the Sun).

For our purposes, we will be considering artificial satellites; those made by people and placed in orbit around the Earth. In the beginning, satellites were made and used by military and civil organizations for the purposes of surveillance and communication. The benefits of using satellites to overcome geographical distance and line-of-sight issues became very clear very early.

As technology grew, and people moved from simply watching television, to using mobile phone, GPS, and Internet services, satellites have increased in number and capability. The telecommunications satellite is the one with which most people are familiar, or at least the one most people imagine when they think of satellites. 

The standard telecommunications satellite is a very large piece of hardware orbiting the Earth above the Equator at 36 000 km. Such a satellite has several specific components and features. Depending on the required function of the satellite, your components, orbital location, and choice of hardware and software can change drastically. Satellite engineers must clearly understand the desired function, and then make choices based on the environments and components which may serve that function.

In order to better understand what a satellite needs, let's think like an engineer! Let us imagine that you want a satellite to hover above your country or continent, providing everyone with phone, television, and internet services. 

In order to send and receive the information, we're going to need an antenna. It must be large enough to catch all the signals sent up by broadcasting stations all over your country, and powerful enough to send that signal to each and every customer on the ground. 

We will need a computer, to encode and decode the signal, to track the satellite's health and location, and coordinate all the functions of the satellite and its components. 

In order to power the satellite, we'll need electrical power, which we can get most easily via solar panels. Sometimes, the satellite may be in shadow, rendering the panels less than useful. In that case, we will need batteries for backup power.

How do we ensure that the satellite is pointed at our country, and not somewhere else, or spinning out of control? We will use an Attitude and Orbit Control System, or AOCS. This includes the software and hardware necessary to know where the satellite is currently pointing and issuing commands necessary to point the satellite to the right place. You will need sensors (Earth, Sun, star) which can point at the objects in parentheses in order to determine how the satellite is oriented, and you will require some sort of system for turning the satellite and keeping it in your desired orientation. These can come in the form of momentum flywheels or gyros (basically spinning wheels), magnetorquers (magnets fixed to your satellite which can interact with the magnetic field of the Earth and turn your satellite), or thrusters (chemical propulsion jets which turn the satellite).

Speaking of propulsion, you may require such a system to help keep your satellite in the right orbit. While space is a near-vacuum, there are effects which can cause a satellite to drift over time. The Earth isn't perfectly spherical so it pulls on satellites in different ways, in different places. The Moon does the same. Even the radiation from the Sun can push satellites out of place. Therefore, you'll likely need fuel and a propulsion system to occasionally fix the satellite orbit. Also, as environmental concerns over space debris become more of a pressing issue, you may need this propulsion system to deorbit the satellite.

Depending on the orbit, (more information on orbits here), your satellite may require some form of thermal control. Electronics do not work well if they become too hot or too cold, so the thermal control system keeps everything at the best temperature. These systems can be as simple as different coloured paints (like how a white shirt feels cooler on a warm day), fans, heaters, or other special materials. This is why many satellites are shown to be wrapped in some sort of golden mesh; this mesh is likely a form of gold or mylar, used to regulate satellite temperature.

Now you know the basics of satellites! It is my plan to move toward discussing specific kinds of satellites, like CubeSats, and some new innovations in the space industry. There are numerous satellite manufacturing companies all around the world and, believe it or not, satellites are a big business. Now that you know the basics, we can begin to talk about this business in greater detail!

Thank you for reading and remember, if you use a cell phone, you have a satellite to thank for it!

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