On a New Six Degree of Freedom Modelling Method for Homing Missiles and its Application for Design/Analysis

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Development of an accurate six-degree-of-freedom (6-DOF) simulation model for homing missiles incorporating seeker servosystem detailed modelling is reported. A new modelling concept for seeker servosystem simulation, the Newtonian equivalent model (NEM) has been evolved, where body motion coupling is modelled through forces and moments transformed to the seeker. The NEM-based modelling of seeker head and its integration in 6-DOF has been discussed. In the presence of body coupling, the simulation model for seeker tracking or pointing error, gimbal angles and inertial line of sight (LOS) rates as measured by the seeker mounted rate gyros have been obtained through the new modelling method. A novel method of obtaining optimum pitch and yaw LOS rates for proportional navigation (PN) guidance mechanisation is formulated based on synthesised sight line rates measured in the seeker inner gimbal axis. This new method has been validated through simulation studies using the 6-DOF model developed and by comparing the results with those obtained by the conventional method of generating LOS rates for PN guidance. Other important applications of the 6-DOF model discussed are guidance and control design validation/tuning seeker feedforward compensation design tuning of switchover point from open-loop to closed-loop PN guidance. Importance of the detailed 6-DOF simulation model as the ultimate performance evaluation tool for the weapon system in terms of both terminal performance and adequacy of seeker field of view, gimbal angle freedom, etc. has been brought out.