4. A guidance system as recited in claim 3 wherein said steerable object includes a guidance point spaced a predetermined distance from the steerable object along its longitudinal axis of motion and said sensing means produces bearings to said object and to said guidance point, said difference means taking the bearing signal difference as the difference between the bearing to the guidance point and the bearing to the second site and taking the rate of change as the rate of change of the difference between the bearing to the object and the bearing to the second site.
5. A guidance system as recited in claim 4 wherein said determining means additionally includes means for generating a bearing error signal corresponding to the bearing signal difference and a rate of change error signal corresponding to the rate of change of the differences between the bearings to the object and to the second site.