Guidance law with circular no-fly zone constraint

The proposed guidance law is used for guiding a missile against a maneuvering target while satisfying a circular no-fly zone (NFZ) constraint. It consists of two parts: virtual-target guidance (VTG) and boundary-constraint handling scheme (BCHS). In order that the missile avoids the NFZ, VTG first maps the actual target to a virtual one, then obtains the relative motion between the virtual target and missile, and finally uses proportional navigation to steer the missile to the virtual target. The missile also hits the actual target when it hits the virtual target because the virtual and actual targets are coincident at this moment. In some cases, especially when the initial velocity vector of the missile points toward the center of the NFZ, if the evasive action taken by VTG is found to be insufficient, then BCHS will be enabled to keep the missile from entering the NFZ unless the target enters the NFZ.