Loosely-coupled GPS/INS state estimation in precision projectiles

A state estimation method for gun-launched precision projectiles using affordable technologies is presented. Navigation algorithms were developed to incorporate flight dynamic models with measurements from inertial sensors and, if available, GPS. GPS is used to estimate an inertial sensor bias which can then be used if GPS is lost later in flight. This novel technique allows GPS to continue to benefit the flight after it is unavailable and allows noisy, low cost sensors to provide a useful state estimate. Simulations were conducted to assess algorithm performance over a range of conditions. These results indicated that the algorithm with only 10 seconds of GPS availability yields a position error of less than 35 m over a 30 s flight. This effort shows that navigation error using coupled GPS/INS is sufficient to increase system accuracy for munitions even if GPS should become unavailable during flight.