Laser Communication Between Mobile Platforms

Practical laser communication is impeded by the inherent strict requirements on agile and accurate steering of the laser beam over a wide angular range that are addressed by the pointing, acquisition, and tracking (PAT) system. While the vehicle carrying the optical instrumentation is in motion, a PAT system is required to compensate for the vibrations applied to the optical platform through the proper application of advanced control laws. This paper presents a feedforward vibration rejection system interacting with an optical tracking system to successfully perform the PAT task. It features a set of inertial navigation sensors to monitor the optical platform orientation, and the optical tracker monitoring the optical alignment errors. The control effort is defined on the basis of both signals and upon amplification drives the actuators of a novel singularity-free full-hemisphere-range robotic manipulator supporting the optical platform. The resultant technology enables two ground vehicles navigating through a difficult terrain to maintain optical connectivity sufficient for reliable laser communication. The paper presents the development of an extended Kalman filter "fusing" the inertial navigation sensor data, the design and implementation of the disturbance rejection/optical tracking control system, and the results of the experimental evaluation of the overall system performance.