The advantages of velocity vector referencing in proportional navigation

Two broad classes of proportional navigation laws are compared with regard to their implementation, analysis, and behavior. The first consists of laws such as the PPN (pure proportional navigation) laws, which are referenced relative to the pursuer velocity vector, and the second consists of line-of-sight (LOS) referenced laws such as TPN (true PN), GTPN (generalized TPN), and GGL (generalized guidance law). It is shown that the latter class has serious drawbacks in terms of implementation and trajectory behavior, which more than offset the limited advantage in analytical treatment exploited hitherto in the literature. Among the major drawbacks are forward acceleration and braking requirements which are difficult to achieve, relative inefficiency in the utilization of control effects, restrictions on initial conditions, for intercept, lack of robustness, and the possibility of unbounded acceleration. From a practical point of view, PPN is a superior guidance law to TPN and its generalizations. The only utility of the LOS-reference laws appears to be to serve as approximations to analyze the more practical and efficient PPN law and its variants