In-lab and On-sky Closed-loop Results of Adaptive Secondary Mirrors with TNO's Hybrid Variable Reluctance Actuators

TL;DR

This paper reports on the development, control, and testing of adaptive secondary mirrors with hybrid variable reluctance actuators, demonstrating their effectiveness in lab and on-sky environments for advanced telescopes.

Contribution

It introduces a new actuator technology for adaptive secondary mirrors and validates its performance through comprehensive lab and on-sky closed-loop tests.

Findings

IRTF-ASM-1 meets all performance requirements in on-sky tests.

Lab tests show effective control of large-format deformable mirrors with hybrid actuators.

The new actuators support thicker facesheets, enhancing mirror robustness.

Abstract

We performed closed-loop lab testing of large-format deformable mirrors (DMs) with hybrid variable reluctance actuators. TNO has been developing the hybrid variable reluctance actuators in support for a new generation of adaptive secondary mirrors (ASMs), which aim to be more robust and reliable. Compared to the voice coil actuators, this new actuator technology has a higher current to force efficiency, and thus can support DMs with thicker facesheets. Before putting this new technology on-sky, it is necessary to understand how to control it and how it behaves in closed-loop. We performed closed-loop tests with the Shack-Hartmann wavefront sensor with three large-format deformable mirrors that use the TNO actuators: DM3, FLASH, and IRTF-ASM-1 ASM. The wavefront sensor and the real-time control systems were developed for the NASA Infrared Telescope Facility (IRTF) and the UH 2.2-meter telescope ASMs. We tested IRTF-ASM-1 on-sky and proved that it meets all of our performance requirements. This work presents our lab setup for the experiments, the techniques we have employed to drive these new ASMs, the results of our closed-loop lab tests for FLASH and IRTF-ASM-1, and the on-sky closed-loop results of IRTF-ASM-1 ASM.