Pointing/tracking control design for a high energy laser system

At MBDA Deutschland GmbH currently a high-energy laser weapon demonstrator is designed with the focus on CRAM (counter rocket, artillery, mortar) and counter UAV scenarios. The demonstrator consists of four industrial fiber lasers that are geometrically coupled in one beam director telescope. With this coupling scheme one telescope can provide sufficient laser energy for a successful CRAM operation. For coarse alignment of the telescope an industrial robot is used; within the telescope two underlying, cascaded control loops of actuated mirrors ensure the ability to position the laser beam with μrad precision on the target. With the first actuated mirror stage (the secondary mirror of the telescope) all laser beams can be controlled simultaneously. This stage is primarily used to compensate for tracking errors due to the limited dynamics of the robot coarse actuation system. The second mirror stage consists of piezo servo loops. One piezo loop each is used to control one laser beam of the telescope. The main task of this actuation stage is to compensate for higher frequency disturbances that could not be attenuated by the other control loops (such as vibrations, atmospheric turbulence, etc.). The paper at hand details the layout of the control loops necessary for pointing the telescope on the target and then for tracking and holding the laser beams on the target. First simulation models and results are presented for pointing and tracking a target with the robot coarse actuation system; then the inner control loops of the telescope are described with special emphasis on the different modes of operation and system interaction/coupling during the engagement cycle. At the end of the paper simulation results are compared with measurements that have been recorded while tracking a drone at the company test site.