Argus Optical Array motion control: novel pointing and tracking solutions for large array telescopes

The Argus Optical Array is an all-sky telescope composed of 900 0.2-m off-the-shelf, wide-field telescopes that covers 20% of the entire sky in each exposure. Using low-noise CMOS detectors, the array reaches g=19.6 in minute-long exposures, while deep coadds will reach g=23.6 every five nights. By observing the entire accessible sky simultaneously, Argus is sensitive to timescales orders of magnitude faster than most time-domain surveys, whose cadence is fixed by the time between visits to the same field. All 900 telescopes are mounted on a single platform that rotates about an axle; thus, operating a complex array telescope is reduced to smoothly tracking using this one axle. This requires few-arcminutes pointing of the system's rotation axis, as it is impossible to make a conventional pointing model for an all-sky telescope. The Argus polar alignment system, first demonstrated on the 8-ft-diameter Argus Array Technology Demonstrator, consists of custom software that controls two off-the-shelf high-load-capacity linear actuators attached to one end of the pointing axle of the Argus Optical Array. The Argus tracking system is a closed feedback loop that consists of an encoder and custom linear actuator, which leverages the large lever arm of the system to easily rotate our telescope platform. This approach was tested on the Argus Array Technology Demonstrator. Here we detail both motion control systems, our automated polar alignment routine, and performance on polar alignment and tracked image quality.