HoverCal + PoloCalC: precise on-flight metrology performance results over CLASS telescope

We present results from efforts to build a drone-based calibration system providing a high-accuracy polarized reference signal for mm-wave telescopes mapping the cosmic microwave background. The multi-rotor drone allows the source to reach the far-field of small aperture telescopes, such as CLASS or SO-SATs, at their nominal elevation angle, providing a reference signal under normal observing conditions. The goal is to achieve calibration accuracy of at least 0.1 degrees on the absolute polarization angle response. Results from three flight campaigns at the CLASS site, Cerro Toco, Chile, tested the on-board metrology system, using GPS and photogrammetry to determine the source's position and orientation during flight. The results indicate the drone's position is known within 10 cm and its polarization angle to better than 0.05 degrees, meeting the system's technical requirements.