Evolution of JWST Contingency Payload Operations for Mitigating NIRSpec Micro-shutter Array Electrical Shorts

TL;DR

This paper discusses how JWST's NIRSpec instrument manages electrical shorts in its micro-shutter array to maintain scientific output, sharing operational strategies refined over two years and future implications.

Contribution

It presents the evolution of contingency procedures for mitigating micro-shutter array shorts in JWST's NIRSpec, including identification, masking, and unmasking strategies to optimize science yield.

Findings

Operational procedures have improved short mitigation effectiveness.

Recovery of multiplexing capacity by unmasking affected shutters.

Operational experience informs future MSA technology use in space missions.

Abstract

The Near-Infrared Spectrograph (NIRSpec) is one of four science instruments on board the James Webb Space Telescope (JWST), which began routine operations in July 2022. As JWST's primary spectroscopic instrument for faint, distant targets, NIRSpec plays a central role in several of the mission's core science goals. Its signature multi-object spectroscopy (MOS) mode enables the simultaneous acquisition of spectra for up to a hundred targets across the field of view, using a micro-shutter array (MSA) comprised of nearly 250,000 individually addressable micro-electromechanical shutters. The MSA is susceptible to occasional electrical shorts, which produce unwanted infrared glow in MOS exposures, rendering them unusable and wasting valuable observatory time. Mitigation requires promptly identifying the affected shutter(s) and masking the corresponding row(s) or column(s) to prevent future activation. However, masking shutters unnecessarily reduces NIRSpec's multiplexing capacity, so it is important to minimize the extent of masking while reliably suppressing the short's effects. More than two years of operations have informed refinements in technical procedures and operational decision-making around short mitigation. This experience also supports new efforts to identify and unmask previously affected rows or columns where shorts have since disappeared, enabling the recovery of multiplexing capacity that would otherwise remain lost. As MSA technology matures toward use in future missions such as the Habitable Worlds Observatory, operational strategies developed for NIRSpec remain relevant beyond JWST. This paper provides an overview of MSA shorts mitigation operations, summarizes shorts observed since the completion of commissioning, and describes the evolving contingency procedures that have enabled continued science productivity from this unique payload.