Estimation on engagement time of proportional navigation guidance system using approximate time constant

By representing the High-order PN guidance system with a single-lag guidance system, a method for the estimation of the engagement time was put forward according to the approximate time constant. The engagement time of high-order PN guidance system is related with PN coefficient regardless of system order. When the system has multi-lag, the high-order system can be represented by an equivalent single-lag. The Approximate time constant of the system is the sum of all the time constants of the one-order lags and for the biquadratic lag system, and the approximate time constant is the first-order coefficient of the binomial. Since the approximate time constant is linear with the engagement time for different PN coefficient, it can be estimated. The method can be extended to the estimation of the engagement time for random order PN guidance system.