Introduction of Missile Control System

INTRODUCTION

The missile flight control system is one element of the overall homing loop. Figure 1 is a simplified block diagram of the missile homing loop configured for the terminal phase of flight when the missile is approaching intercept with the target. The missile and target motion relative to inertial space can be combined mathematically to obtain the relative motion between the missile and the target. The terminal sensor, typically an RF or IR seeker, measures the angle between an inertial reference

and the missile-to-target line-of-sight (LOS) vector, which is called the LOS angle. The state estimator, e.g., a Kalman filter, uses LOS angle measurements to estimate LOS angle rate and perhaps other quantities such as target acceleration. The state estimates feed a guidance law that develops the flight control commands required to intercept the target. The flight control system forces the missile to track the guidance commands, resulting in the achieved missile motion. The achieved missile motion alters the relative geometry, which then is sensed and used to determine the next set of flight control commands, and so on. This loop continues to operate until the missile intercepts the target. 

In the parlance of feedback control, the homing loop is a feedback control system that regulates the LOS angle rate to zero. As such, the overall stability and performance of this control system are determined by the dynamics of each element in the loop. Consequently, the flight control system cannot be designed in a vacuum. Instead, it must be designed in concert with the other elements to meet overall homing-loop performance requirements in the presence of target manoeuvre and other disturbances in the system, e.g., terminal sensor noise (not shown in Fig. 1), which can negatively impact missile performance.

Figure 1. The flight control system is one element in the missile homing loop.

 The inertial missile motion controlled by the flight control system 

combines with the target motion to form the relative geometry 

between the missile and target. The terminal sensor measures

 the missile-to-target LOS angle. The state estimator forms 

an estimate of the LOS angle rate, which in turn is input 

to the guidance law. The output of the guidance law is the 

steering command, typically a translational acceleration.The flight 

control system uses the missile control effectors, such as 

aerodynamic tail surfaces, to force the missile to track steering 

commands to achieve a target intercept.