GPS–INS INTEGRATION REQUIREMENTS FOR ROBUST NOE HELICOPTER NAVIGATION

The integration of a Global Positioning System (GPS) receiver with a strapdown Inertial Navigation System (INS) in order to provide accurate, robust navigation capability for a modern attack helicopter is examined. The attack helicopter mission environment places unique requirements on navigation systems. Precision navigation capability is required for applications including target handover, automatic hover-hold, and automated pilotage systems now under development. However, terrain masking during Nap-of-the-Earth (NOE) flight restricts the availability of GPS satellite signals which can reduce the amount of data provided by a GPS receiver. Two GPS–INS integration methods that have been used in integrated navigation system designs, (1) providing the INS Kalman filter with pseudorange and pseudorange-rate measurements for each tracked GPS satellite and (2) providing the INS Kalman filter with GPS receiver derived position and velocity fixes, are considered for an attack helicopter navigation system. The navigation performance of these two schemes is compared for a simulated NOE attack helicopter mission over actual terrain. The performance analysis shows that integration of the GPS receiver with an INS using pseudorange and pseudorange-rate data provides overall navigation accuracy of about twice that of position and velocity fix integration. It can also significantly increase attack helicopter mission effectiveness in an NOE environment.