OPERATION OF A SINGLE-CHANNEL, SEQUENTIAL NAVSTAR GPS RECEIVER IN A HELICOPTER MISSION ENVIRONMENT

The NASA Ames Research Center is conducting a research program to determine the feasibility of Differential GPS as a precision-approach and landing-guidance aid in remote areas. Based on preliminary studies conducted under this program, it has been shown that to achieve the required accuracy using the proposed GPS civilian signal (C/A code), improvements are necessary to reduce the vertical navigation error component. This paper presents the results from an initial series of flight tests conducted in the NASA SH-3G helicopter to better understand the nature of the errors associated with the dynamic performance of a NAVSTAR GPS single-channel receiver in a typical helicopter approach, and to direct research toward reducing the vertical navigation error component. Navigation solutions obtained during the sequential tracking of four satellites and the solutions for the baro-altitude-augmented, three-satellite mode of operation of the GPS Z-Set receiver were compared. The effects of the constellation geometry on system performance are noted.