Abstract: In an integrated satellite navigation system where satellite fixes periodically establish the position of a ship plying a course within the range of a chain of radio ranging stations, ship velocities are accurately determined in the interval between satellite fixes to chart the course between fixes by establishing difference values between successive RF signal transit times for each of a plurality of radio ranging stations. A set of functions dependent upon the difference values for transit times related to each station is stored, retaining the most recent and discarding the most aged of the set. Velocity signals representative of the motion of the ship are then periodically generated by utilization of the sets of difference functions. Preferably, the sets of difference functions are modified to give the most recent members of each set the greater weight.