'MOHAWK' : a 4000-fiber positioner for DESpec

TL;DR

This paper introduces a modular, low-cost 4000-fiber positioner for DESpec using Echidna tilting spine technology, addressing challenges of curvature and pitch with off-the-shelf actuators and rapid reconfiguration.

Contribution

It presents a novel, highly modular design for a large fiber positioner that overcomes curvature and pitch challenges, with proven prototypes and estimated throughput losses.

Findings

Prototyped actuators achieve 7 micron accuracy within 15 seconds.

Design accommodates the curved focal plane and small pitch without major issues.

Estimated throughput loss is about 15%, with 6.3% due to tilting-spine technology.

Abstract

We present a concept for a 4000-fibre positioner for DESpec, based on the Echidna 'tilting spine' technology. The DESpec focal plane is 450mm across and curved, and the required pitch is ~6.75mm. The size, number of fibers and curvature are all comparable with various concept studies for similar instruments already undertaken at the AAO, but present new challenges in combination. A simple, low-cost, and highly modular design is presented, consisting of identical modules populated by identical spines. No show-stopping issues in accommodating either the curvature or the smaller pitch have been identified, and the actuators consist largely of off-the-shelf components. The actuators have been prototyped at AAO, and allow reconfiguration times of ~15s to reach position errors 7 microns or less. Straightforward designs for metrology, acquisition, and guiding are also proposed. The throughput losses of the entire positioner system are estimated to be ~15%, of which 6.3% is attributable to the tilting-spine technology.