"Global Positioning Satellites Navigators continually struggle to find better tools to help them determine their location. The first explorers used the sun and stars to help them steer a straight course, but this method of navigation only worked under clear skies. Magnetic compasses were developed yet could only be used to determine longitude, not latitude. Finally, the mechanical clock, in conjunction with the compass, provided navigators with the most accurate method of determining location. Today, most navigators use a handheld device that functions in concert with a series of 24 orbiting satellites. This network, the Global Positioning System (GPS), can determine your position and altitude anywhere on earth. The GPS pinpoints your location by sending out radio signals to locate any 4 of the 24 orbiting GPS satellites. Once the satellites are found, the GPS measures the length of time it takes for a radio signal to reach the handheld receiver. When the time is determined for each of four satellites, the distance is calculated, and the longitude, latitude, and altitude are displayed on the screen [Fig. 3.39(a)]. The GPS was first developed solely for military use. Eventually, the GPS was made available for civilian businesses. Shipping, airline, farming, surveying, and geological companies made use of the technology. Today, GPS receivers are affordable and are used by the general public [Fig. 3.39(b)]. More sophisticated receivers not only locate a position, but can also guide the navigator to a predetermined location. Several automobile manufacturers have included GPS receivers as an option in their cars. Such receivers come complete with voice commands, such as "Turn left at the next traffic light," as part of their option packages.Tesla is a unique automobile as it is considered to be the first-of-its-kind, fully electric and high-performance electric vehicle. Prior to the Tesla, electric cars were hybrid vehicles that relied on a combination of electric power