Figure 2 illustrates how an artificial satellite can orbit the Earth. In theory, if a cannon is fired fairly weakly, the path of the cannonball will be that of a parabolic arc and will land perhaps a few hundred yards away. The numbered frame 1 shows a cannon using a little more gunpowder, which causes the cannonball to shoot a little bit farther. In this situation, the ball lands perhaps a few hundred miles away. We can see just a little of the Earth's curvature, but it does not really affect anything. In the second numbered frame, using a super-shooter, the cannonball is shot hard enough that it travels several thousand miles. This frame illustrates that the curvature of the Earth has had an effect. The ball travels much farther than it would have had the Earth been flat. Finally, in the third numbered frame, a mega-super-big cannon fires the cannonball at the unbelievable velocity of 5 miles/second (nearly 17,000 miles/hour; the fastest jet planes can fly 2 or 3 thousand miles/hour). The result of this shot is that the ball misses the Earth as it falls.

Figure 2. An illustration of an artificial satellite launch. copyright

However, the Earth's gravitational pull causes it to both continuously change direction and continuously fall. The result is a "cannonball" which is orbiting the earth. In the absence of gravity, however, the original throw (even the shortest, slow one) would have continued in a straight line, leaving the Earth far behind.

An artificial satellite is a manufactured object that orbits Earth or something else in space on a continual basis. Satellites are used to study the universe, to help forecast the weather, to transfer telephone calls and to assist in ship and aircraft navigation. Specifically, communications satellites serve as relay stations, receiving radio signals from one location and transmitting them to another. A communications satellite can relay several television programs or many thousands of telephone calls at once. They are used to bounce messages from one part of the world to another.

Figure 3. The basic components of a communications satellite link copyright

Every communications satellite involves the transmission of information from an originating ground station to the satellite, followed by a retransmission of the information from the satellite back to the ground (see Figure 3). The retransmission may either be to a select number of ground stations or it may be broadcast to everyone in a large area.

Space shuttles carry some satellites into space, but most satellites are launched by rockets that fall into the ocean after the fuel is used up.

A cellular phone can be described as a very sophisticated radio. They are a type of wireless communication device that uses many small cells with a base station and a cell phone tower at the center of each cell. These cells have extensive frequencies that allow many thousands of people to use cell phones at the same time. In this process, cellular calls are transferred from base station to base station as a user travels from cell to cell. A cellular network is composed of cellular towers. In essence, when a call is placed from your cell phone, it travels by radio waves to a cellular tower that picks up the specific signal from your phone. These cellular towers are thought of as cells, with each cell able to typically pick up a signal within 10 square miles. The signal is then sent to a Mobile Telephone Switching Office (MTSO) which handles calls from several towers — called a cluster. The MTSO transfers the signal to a local phone line that sends the signal to the final destination via landline, microwave signals or satellite. The MTSO senses when the signal is becoming weak and hands your call off to the next tower — or the MTSO in the next cluster. It controls the quality of your link by keeping you connected to the best possible signal as you move from cell to cell. When you have traveled beyond the range of the towers, the signal is lost and you cannot make or receive calls.

Satellite phones do not use cells or cell towers for sending/receiving calls. Most satellite phones use Low Earth Orbiting (LEO) communication satellites. When a satellite phone is turned on, the signal goes up to any number of satellites in a compatible constellation (group of satellites) where it is then registered with the constellation. When a call is made through the satellite phone, the signal goes to the satellites and then is directed down to a ground station and then further directed to the call destination. The call can be directed to a land-line as well as a cellular network and the reverse is also true. This process allows the satellite phone to be used in the middle of no where — great distances from any cellular phone tower — and thus providing an essential form of communication for those who travel to the beyond!