As technological improvements continue to lower manufacturing costs, astrographic telescopes and cameras are becoming cheaper and more accessible to a wider community. The Argus Optical Array (AOA) capitalizes on these advances to create an all-sky, high-cadence telescope array with arcsecond-resolution and a cost in the $20M range. The completed array will have a 5-m class collecting area consisting of over 900 individual telescopes observing the entire Northern sky simultaneously at a 1-minute cadence (and capable of observing at second-timescales). The Argus Array Technology Demonstrator (A2TD) enables the investigation of the performance of telescopes, cameras, climate control, precision tracking and pointing systems for inclusion in the completed AOA. It consists of nine 8-inch telescopes under a hemispherical enclosure mounted onto the Hercules Mount, a semi-fixed, equatorial mount. The mount adjusts its polar axis alignment via two high-precision linear actuators while supporting a load of over 180 kg including counterweights. The dome is decoupled from the platform containing the telescopes to minimize the effect of windshake during observations. Sidereal tracking is performed by two linear actuators which connect to the outer dome and the telescope platform separately and track synchronously at arcsecond precision. The Hercules mount was constructed from a combination of low-cost commodity materials, with only three key components requiring precision CNC machining. Systems tested on the Hercules Mount will scale or transfer directly to the next instrument in the Argus series of prototypes: Argus Pathfinder. Here we present on-sky results of the Hercules Mount and our plans for the next generation of Argus prototypes.
The Argus Optical Array will be the first all-sky, arcsecond-resolution, 5-m class telescope. The 55 GPix Array, currently being prototyped, will consist of 900 telescopes with 61 MPix very-low-noise CMOS detectors enabling sub-second cadences. Argus will observe every part of the northern sky for 6-12 hours per night, achieving a simultaneously high-cadence and deep-sky survey. The array will build a two-color, million-epoch movie, reaching dark-sky depths of mg=19.6 each minute and mg=23.6 each week over 47% of the entire sky, enabling the most-sensitive-yet searches for high-speed transients, gravitational-wave counterparts, exoplanet microlensing events, and a host of other phenomena. In this paper we present our newly-developed array arrangement, which mounts all telescopes into the inside of a hemispherical bowl (turning the original dome design inside-out). The telescopes’ beams thus converge at a single “pseudofocal” point. When placed along the telescope’s polar axis, this point does not move as the telescope tracks, allowing every telescope to simultaneously look through a single, unmoving window in a fixed enclosure. This telescope bowl is suspended from a simple free-swinging pivot (turning the usual telescope mounting support upside-down), with polar alignment afforded by the creation of a virtual polar axis defined by a second mounting pivot. This new design, currently being prototyped with the 38-telescope Argus Pathfinder, eliminates the need for a movable external dome and thus greatly reduces the cost and complexity of the full Argus Array. Coupled with careful software scope control and the use of existing software pipelines, the Argus Array could thus become one of the deepest and fastest sky surveys, within a midscale-level budget.
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.
The Argus Optical Array is a synoptic survey instrument that will use 900 commercial off-the-shelf telescopes to cover a composite all-sky of view with a total collecting area equivalent to a 5-meter telescope. We are currently carrying out a staged development process, leading up to the construction of the 38-telescope Argus Pathfinder system, which will observe the entire Northern sky between −20◦ < δ < 72◦ each night for 15 minutes per field. Argus Pathfinder is currently scheduled for a Q3 2022 deployment to the Pisgah Astronomical Research Institute in Rosman, NC. The Argus Array Technology Demonstrator (A2TD) is the first in this series of prototype instruments, and consists of 9-telescopes in a fiberglass enclosure on a tracking platform. The A2TD is a tool for rapid development, testing, and performance validation of the essential subsystems of the Argus Array design, including a custom-developed tracking drive and polar alignment system, thermal environment control, optical windows, and observatory control. The A2TD is also used for on-sky validation of telescope and camera pairs that have been bench-aligned, and for development of observatory automation and control software that are either directly transferable or scalable to later development stages, including the Argus Pathfinder. In this paper, we present the development process and design of the Argus Technology Demonstrator, and highlight early results from on-sky testing with the instrument.
Wide-field surveys using small-aperture, mass-produced telescopes have the potential to lower instrument hardware costs by orders of magnitude. The Argus Array series of instruments will open new pathways into the study of optical transients via high-cadence, all-sky imaging. The first prototype, the nine-telescope Argus Technology Demonstrator, is already onsky and validates novel concepts in tracking and high-speed data reduction. Next, the fully funded Argus Pathfinder consists of 38 telescopes on a single mount, and will observe the sky between -20° and +72° declination over the course of each night. The project is planned to culminate with the Argus Optical Array observing 20% of the entire sky simultaneously with 900 telescopes at cadences as fast as 1 second. As the number of telescopes increases, so do the maintenance requirements. For a standard open-air array on many mounts, this could result in operations costs far in excess of those of an equivalent monolithic telescope and lead to inconsistent sky coverage while parts of the array are offline. To limit wear and the need for cleaning, re-alignment and focusing, we seal our telescopes in a filtered and air-conditioned environment. This enclosure will be heavily insulated and maintained within a temperature range small enough to prevent measurable changes in telescope focus. Cameras and other power sources in the enclosure are water-cooled and the heat is removed to an isolated service module containing the array’s HVAC and support equipment. From there, the system temperature is maintained at a few seasonally changed set-points. This paper presents the design of the Pathfinder enclosure and environmental control system.
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