Presentation of a method for obtaining a navigation capability as a bonus to a communication satellite system. The Memorandum is primarily concerned with the technology of determining a user vehicle's position from a single satellite by obtaining multiple measurements of range and range-rate data. The computational method is based on a "six-element fix" where three unknown position components and three unknown velocity components are determined from a set of measurements of range and range-rate data. In principle, it is an orbit determination process in reverse. A simplified model of the process simulated many examples with vehicle speeds ranging from 20 K for surface vessels to 2000 K for supersonic aircraft and with satellite altitudes ranging from 500 n mi to synchronous, both polar and equatorial. Results indicate that satisfactory aircraft navigation accuracies may be achieved for orbital altitudes of less than 4000 n mi. 75 pp.