Azimuthal Rotator/Slew Drive Control System and Characterization for Precision Pointing in Field Testing the POEMMA Balloon with Radio Project

The Probe of Extreme Multi-Messenger Astrophysics Balloon with Radio project, a NASA super-pressure balloon mission aiming to study Ultra-High-Energy Cosmic Rays, very high energy neutrinos, and High-Altitude Horizontal Airshowers, requires the precise pointing of the ~3,000-pound telescope array to achieve sub-1° pointing accuracy during field testing. Requirements first call for robust mounting solutions for the integrated system of the trailer bed to the azimuthal rotator to the telescope array, ensuring secure transportation and deployment of the full gondola system for field testing. Design specifications led to the development of a system consisting of a high-torque Azimuthal Rotator by utilizing a SlewMaster slew drive and a geared stepper motor with an integrated pulse controller. Controlled rotation in azimuth is crucial for accurately scanning and characterizing the full optical field-of-view of the telescope system using stationary light sources during calibration. The control system must rely on a relative-axes navigation method for accurate positioning, which is dependent on mitigating mechanical error. The primary contribution here is the precise characterization of system backlash through the integration of physical limit switches to establish a repeatable, high-fidelity zero reference point. Automated pulse sequences execute controlled, bidirectional rotation. The measured data, in motor steps, quantifies the total mechanical backlash in the high-reduction gear train. This contribution plans to present the control architecture, testing methodology, and report the preliminary measurements quantifying total system backlash. Safety regulations also call for control switches for an emergency stop and operator presence control.