  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.
