This report describes a computer program designed to analyze aspects of the geometric performance of pseudoranging navigation satellite (navsat) systems for users either on earth or in earth orbit. A navsat system includes a fleet of satellites, each with an accurate clock that transmits ephemeris, time, and other signals. These signals can be received by relatively small, inexpensive equipment, thus enabling the user to compute his position and time accurately. The NAVSTAR/Global Positioning System (GPS) is such a system, and its overall user accuracy can be broken down into two components which, when multiplied together, yield an estimate of the user's position and/or time accuracy. These two components are analyzed in this report. The first depends on the relative geometry among the navsats being employed and the user's location, and the second involves a determination of system errors. This report was prepared as part of a Project AIR FORCE study entitled "Space Warfare Issues," and should be of use to military and civilian defense analysts responsible for the design, use, and survivability of GPS and other U.S. space-related systems.