The InfraRed Imaging Spectrograph (IRIS) is the first-light client instrument for the Narrow Field Infrared Adaptive Optics System (NFIRAOS) on the Thirty Meter Telescope (TMT). IRIS includes three natural guide star (NGS) On-Instrument Wavefront Sensors (OIWFS) to measure tip/tilt and focus errors in the instrument focal plane. NFIRAOS also has an internal natural guide star wavefront sensor, and IRIS and NFIRAOS must precisely coordinate the motions of their wavefront sensor positioners to track the locations of NGSs while the telescope is dithering (offsetting the telescope to cover more area), to avoid a costly re-acquisition time penalty. First, we present an overview of the sequencing strategy for all of the involved subsystems. We then predict the motion of the telescope during dithers based on finite-element models provided by TMT, and finally analyze latency and jitter issues affecting the propagation of position demands from the telescope control system to individual motor controllers.
@article{arxiv.1808.07504,
title = {The Infrared Imaging Spectrograph (IRIS) for TMT: closed-loop adaptive optics while dithering},
author = {Edward L. Chapin and Jennifer Dunn and David Andersen and Glen Herriot and Dan Kerley and Takashi Nakamoto and Jimmy Johnson and Lianqi Wang and Gelys Trancho and Eric Chisholm and Brent Ellerbroek and Kim Gillies and Yutaka Hayano and James Larkin and Luc Simard and Mark Sirota and Ryuji Suzuki and Bob Weber and Shelley Wright and Kai Zhang},
journal= {arXiv preprint arXiv:1808.07504},
year = {2018}
}