News‎ > ‎

How do Satellites Work?

posted Jul 24, 2011, 3:41 PM by Nathan Eliason

Now, when we think of satellites, we see daily services like television and internet using space to deliver better performance. Just more than a generation ago, however, the launch of a satellite would put the nation in a standstill, as the 1957 Russian satellite Sputnik fueled a Race to the Moon. Panic swept through the nation as we feared the potential danger we were in with a potential enemy’s aircraft above our heads.

In reality, a satellite is any object in orbit around another object, whether it is natural or man-made. Currently, there are about 3000 total artificial satellites (man-made) in orbit around Earth, only around 600 of which are reported to be active. They aid us in our everyday lives, and many of us couldn’t live out our lives as we are without them.

A satellite is composed of three basic parts (this is all extremely simplified. This is rocket science, after all): A power source, a control system, and communication capabilities with transmitters and receivers on Earth. These man-made satellites most often include cameras, solar cells, radio receivers and transmitters, rocket motors, rocket fuel, communication and command antennas, and batteries.

To put a satellite in orbit, complicated math is involved. The launch must be precisely planned to create a delicate balance between Earth’s gravity pulling the machine back to Earth, and its own momentum pulling it around and away from Earth.  When a ball is thrown, for example, its own momentum pulls it up and away from Earth, yet the gravity from Earth on the ball pulls it back to the ground. Throw it too hard, and it will escape Earth’s orbit and fly into uncharted space with no gravitational pull back to Earth. The trick with satellites is to get in between the two regions, as to where Earth’s gravity will pull it back to Earth, but its own momentum will cause it to move around the planet, causing it to continually “fall” around the Earth. Any slower than 17,000 miles per hour, and the satellite will crash back to Earth’s surface. Too fast (around 13,500 mph), and the satellite will leave Earth’s gravity and become useless.

Satellites in low orbit, closer to Earth, circle the planet about 14 times daily. Its footprint, or viewing area of Earth, is always slightly below half of the planet, like we (at a full moon), can only view nearly half of the moon at one time (and incidentally the same half all the time, but that’s a different story). Satellites that are further from Earth, high-altitude satellites, travel around Earth in the same amount of time as its revolutionary period (one day), meaning that the satellite will always be looking at the same patch of Earth, enabling users on Earth to keep their satellite dishes (such as DIRECTV® and Dish Network®) focused on one location, while the satellite stays in the same spot in our sky (as viewed from Earth) all the time. This requires the satellite to be almost exactly 22,237 miles from Earth’s equator.

For example, your satellite television provider (assuming you have one) launches a satellite into space, which reaches 22,237 miles above Earth and flies around once each day in the same direction our planet is turning. Then, with the satellite dish on your house, they simply calibrate the dish to point exactly to that satellite, and because the satellite doesn’t appear to move from the surface of Earth, you don’t have to move your dish ever.

If you have a satellite-powered GPS, then you use a number of satellites every time you navigate somewhere. There are 24 satellites in low-orbit around Earth, whose location is precisely calculated at all times. Your GPS then finds at least four satellites and measures the time that a signal goes from the GPS to the satellite and back, and then uses that to find the distance from each satellite, giving you your exact position on Earth. Your GPS is actually intentionally inaccurate, to protect civilians for security reasons. The military, however, can rely on their GPS units to be accurate within a centimeter 95% of the time.