A projectile which uses a bang-bang type guidance law is hunched, and its goal is to hit a fixed target whose centre is located on the ground. Using stochastic optimal control, the performance of the projectile is compared with cases where an optimal guidance law, or a saturated proportional navigation law, are being applied using the same airframe.
1. Introduction
Conventional missile systems make use of seekers which are mounted on some sort of gimbal system inside the missile, for detection and tracking of the target. The gimbals allow the seeker to be inertially stabilized, and it is then possible to implement a proportional navigation guidance law. The proportional navigation guidance law provides in general very good guidance accuracies. The alternative to mounting the seeker on gimbals is to fix the seeker to the missile airframe in the so-called strapdown configuration. To implement a proportional navigation guidance law using a strapdown seeker requires the use of an on-board computer and some additional sensors. All the above schemes are complex, costly and difficult to implement in a high-g launch environment.
In this work a cheaper option for a guidance scheme, although a less accurate one, is discussed. This scheme uses the concept of a wind stabilized seeker. The concept of a wind stabilized seeker makes use of a seeker mounted on a "sting" which protrudes from the front of the missile. The seeker is mounted on a universal joint, and has a housing which is aerodynamically shaped so that it will align itself with the relative wind vector. The seeker sightline is therefore aligned with the missile flight path, irrespective of airframe attitude. The seeker can then measure the error angle between the seeker's flight path and the seeker-to-target line-of-sight. By using the seeker's outputs to control the flight surfaces on the missile airframe, the guidance loop tries to zero this error angle. Henceforward, it is assumed that the system is to be used against targets on the ground and that the projectile is unpowered after initial launch.
This paper deals with the guidance of a projectile which uses a wind stabilized seeker. Using stochastic optimal control, three guidance laws are considered, that is, an optimal guidance law, a saturated proportional navigation law and a bang-bang guidance law. However, from these three laws only the bang-bang guidance law can be implemented on the above-mentioned projectile, and the study of the first two laws is done for the sake of the evaluation of the performance of the projectile acting under the third guidance law.
This work is to a large extent a continuation of [1], and the methods applied here are the same as those applied in [1]. However, the physical problem dealt with here differs from the one dealt with in [1].