Global Positioning System Applications

The space-based Navstar Global Position­ ing System (GPS), which is scheduled to achieve full operational status by late 1988, will consist of 18 active satellites placed around six orbital rings at 10,898 nautical miles above the earth. Every other ring will contain an extra satellite that will function as an active on-orbit spare. This regular and precise constellation of GPS satellites will provide continuous, three-dimensional global navigation coverage to users worldwide. Average positioning accuracies of 15 meters or less are anticipated by the military. This extraordinary precision has been demonstrated repeatedly under field-test conditions in both the United States and Western Europe. Other tests indicate that relative (differential) navigation, which employs user sets rigged to communicate their navigation solution to one another, can achieve substantially better results. Relative errors of only 1 or 2 meters have been demonstrated with existing equipment under realistic field-test conditions. Both military and civilian users are expected to find broadranging applications for the accurate and reliable navigation provided by the GPS. Various branches of the military intend to purchase more than 20,000 user sets in this century, and the Wall Street journal projects an additional 250,000 will be pur­ chased by civilian users. The final sections of this technical paper discuss the opera­ tional characteristics and practical benefits of the following specific civil uses of the Navstar system: (1) air traffic control, (2) time synchronization, (3) offshore oil exploration, (4) iceberg tracking, and (5) dinosaur hunting.