A comparison of state space, range space, and carrier phase differential GPS/INS relative navigation

The first ground test results of the UCLA formation flight control computer (FFCC) are presented. The FFCC are designed to calculate real time, relative states of multiple aircraft accurately enough to fly two F-18 A/C autonomously in formation flight for a drag reduction experiment. This paper compares three schemes of differing complexity for the estimation of relative position, velocity, and attitude of two FFCC. Each scheme processes measurements from a GPS receiver and an INS on each vehicle. In the first scheme, each FFCC estimates its own absolute state using an extended Kalman filter (EKF) and the relative state is found by differencing the absolute state estimates from each filter. In the second scheme, one vehicle processes the single vehicle EKF while the second processes the differential range and Doppler measurements to estimate the relative state. In the third scheme, differential carrier phase measurements are added to the relative state estimation filter. The third scheme meets the target values for flying two NASA F-18 A/C in flight formation. Relative position is estimated within 10 cm, and relative attitude within 0.5 deg.