In the not-so-distant past, the mention of satellites inspired images of the space program and science fiction. Although they do orbit the Earth, satellites have many applications here on Earth. The use of satellites has become common in the ever-changing landscape of modern civilian and military technology. Satellites allow people to receive data and reach out from even the most remote of locations.
Phones
A satellite phone is a form of wireless communication device that transmits conversations and data to satellites in orbit over the Earth. These signals then are sent from the satellites to a receiver on the ground, which then routes the call through local telephone networks. Satellite phones differ from regular cell phones in that they do not rely on communicating with cell towers on the ground, which may not be close enough for use in remote areas. This technology enables callers to communicate with someone from anywhere in the world, provided that there is adequate coverage by satellites in orbit. These types of phones communicate with two different types of satellites, low-orbit and geosynchronous. Low-orbit satellites move very fast at an altitude of more than 400 miles above Earth's surface and orbit the planet every 60 to 90 minutes. Geosynchronous satellites are more powerful and fewer in number, orbiting above a single point on Earth at an altitude of up to 20,000 miles. While they provide larger areas of coverage than low-orbit satellites, there is a considerable transmission delay, or lag, due to their distance from Earth. Phones that work with low-orbit satellites also require less power than those that transmit to geosynchronous satellites, meaning that they also tend to be cheaper and smaller. Like with cellular phones, transmissions to and from a satellite phone depend on line-of-sight coverage, meaning that a phone must be within the line of sight of a satellite. This means that the best way to communicate using a satellite phone is to be outside. Satellite phones can be prohibitively expensive due to the cost of building and launching communications satellites, but the cost is gradually declining due to improving technology.
- How and When to Buy a Satellite Phone
- Satellite Phones: What to Know and Where They Go (PDF)
- Satellite Communications
- Satellite Telephony
Televisions
Satellite television programming is broadcast through a signal from orbiting satellites. This signal is caught by a small dish-like antenna that is referred to as a satellite dish. These dishes are small enough to sit on one's roof, on the side of a house, or in a backyard without taking up a large amount of space or being overly obtrusive. Most often, satellite television subscribers receive select programming sent from a direct broadcast satellite, or DBS, provider. Consumers sign up and purchase packaged programming from these DBS providers. The DBS provider receives signals from the programming source. The signals are then sent from the DBS broadcast center to the satellite, which sends the signal back down toward Earth. The consumer who has paid for the DBS package picks up the signal with their satellite dish, which sends the programming to the receiver connected to their television. There are many benefits to satellite television, such as hundreds of available channels and high-quality picture and sound as well as the potential for access to media feeds from around the world.
- Satellite Reception
- The Birth of Satellite TV 50 Years Ago
- Satellite Programming
- Receiving Television Broadcast Stations From Satellite TV Companies
- What Are Satellites Used For?
GPS
The Global Positioning System, or GPS, is a satellite navigation system owned by the U.S. and set into place by the U.S. Department of Defense. The system, which consists of satellites orbiting the earth, is operated and maintained by the 50th Space Wing out of Schriever Air Force Base in Colorado. There are three segments that make up the system: the space, control, and user segments. The actual satellites are a part of the space segment, and roughly 95 percent of the time, there are a minimum of 24 GPS satellites in operation. These satellites circle Earth at an altitude of 12,550 miles, which is considered a medium earth orbit, every 12 hours. A minimum of four satellites are placed on each of six orbital planes that surround the planet. This configuration ensures that at least four of the satellites are available to users regardless of where they are on Earth.
The second GPS segment, which is the control segment, consists of stations and antennae that track, analyze, send commands to, and monitor the GPS satellites. Although the master control station is located in Colorado, monitoring stations are found around the U.S. and in locations in countries such as Australia, Bahrain, Ecuador, and South Africa. The master control station's job is to control and maintain the accuracy of the satellites' placement and to send them navigational messages. In addition, information received by the monitoring stations is sent to the master control station, where it is used not only to update navigational messages sent to the satellites but also to help determine their exact location.
GPS equipment such as a receiver makes up the user segment. This equipment is how people use GPS signals for navigational or tracking purposes. While GPS is an important tool for the military, it is also used by civilians around the world. GPS applications include time synchronization, environmental data collection, and collecting accurate positioning information for rescue efforts. GPS has also become a popular tool for drivers, who use it for mapping out trips or finding destinations. In aviation, it is used to improve navigation and, as a result, increase flight safety.
- The GPS
- The Evolution of GPS
- Satellite Technology (PDF)
- Understanding the Global Positioning System
- GPS Applications
- Global Positioning System