  With its first flight in 2018, Micro-X became the first program to fly
Transition-Edge Sensors and their SQUID readouts in space. The science goal was
a high-resolution, spatially resolved X-ray spectrum of the Cassiopeia A
Supernova Remnant. While a rocket pointing error led to no time on target, the
data was used to demonstrate the flight performance of the instrument. The
detectors observed X-rays from the on-board calibration source, but a
susceptibility to external magnetic fields limited their livetime. Accounting
for this, no change was observed in detector response between ground operation
and flight operation. This paper provides an overview of the first flight
performance and focuses on the upgrades made in preparation for reflight. The
largest changes have been upgrading the SQUIDs to mitigate magnetic
susceptibility, synchronizing the clocks on the digital electronics to minimize
beat frequencies, and replacing the mounts between the cryostat and the rocket
skin to improve mechanical integrity. As the first flight performance was
consistent with performance on the ground, reaching the instrument goals in the
laboratory is considered a strong predictor of future flight performance.
