a sensor system uses ground emitters to illuminate a projectile in flight with a polarized rf beam . by monitoring the polarization modulation of rf signals received from antenna elements mounted on the projectile , both angular orientation and angular rate signals can be derived and used in the inertial solution in place of the gyroscope . depending on the spacing and positional accuracies of the rf ground emitters , position information of the projectile may also be derived , which eliminates the need for accelerometers . when rf signals of ground emitter / s are blocked from the guided projectile , the sensor deploys another plurality of rf antennas mounted on the projectile nose to determine position and velocity vectors and orientation of incoming targets .