Free flight testing of missile designs is generally necessary to confirm that accurate estimates have been made of effects due to the change in size from wind tunnel model to full scale missile and of effects arising from the flight dynamic behaviour of the missile. The amount of such testing is generally limited by the high costs involved and so every effort is made to obtain the maximum information from each flight trial. During recent years parameter estimation techniques have been developed to provide superior methods for analysis of free flight tests. They enable the analyst to extract the required data with greater accuracy from fewer tests than has previously been possible. The old equation error methods relied on measuring all the variables characterising the projectile motion and using the equations of motion to obtain a relationship between aerodynamic forces and moments and translational and angular velocities of the vehicle.