In-flight performance of the NIRSpec Micro Shutter Array

TL;DR

The paper evaluates the in-flight performance of JWST's NIRSpec Micro Shutter Array, highlighting its high success rate, usability, and operational readiness for science, with insights into failure modes and proposed improvements.

Contribution

It provides a comprehensive assessment of the MSA's in-flight performance, including failure analysis and operational plans to enhance reliability.

Findings

96% success rate in shutter commands during commissioning

82.5% of unvignetted shutters are usable for science

Marginal increase in failed open/closed shutters consistent with ground tests

Abstract

The NIRSpec instrument on the James Webb Space Telescope (JWST) brings the first multi-object spectrograph (MOS) into space, enabled by a programmable Micro Shutter Array (MSA) of ~250,000 individual apertures. During the 6-month Commissioning period, the MSA performed admirably, completing ~800 reconfigurations with an average success rate of ~96% for commanding shutters open in science-like patterns. We show that 82.5% of the unvignetted shutter population is usable for science, with electrical short masking now the primary cause of inoperable apertures. In response, we propose a plan to recheck existing shorts during nominal operations, which is expected to reduce the number of affected shutters. We also present a full assessment of the Failed Open and Failed Closed shutter populations, which both show a marginal increase in line with predictions from ground testing. We suggest an amendment to the Failed Closed shutter flagging scheme to improve flexibility for MSA configuration planning. Overall, the NIRSpec MSA performed very well during Commissioning, and the MOS mode was declared ready for science operations on schedule.