  IGR J17591-2342 is an accreting millisecond X-ray pulsar discovered in 2018
August in scans of the Galactic bulge and center by the INTEGRAL X-ray and
gamma-ray observatory. It exhibited an unusual outburst profile with multiple
peaks in the X-ray, as observed by several X-ray satellites over three months.
Here we present observations of this source performed in the X-ray/gamma-ray
and near infrared domains, and focus on a simultaneous observation performed
with the Chandra-High Energy Transmission Gratings Spectrometer (HETGS) and the
Neutron Star Interior Composition Explorer (NICER). HETGS provides high
resolution spectra of the Si-edge region, which yield clues as to the source's
distance and reveal evidence (at 99.999% significance) of an outflow with a
velocity of $\mathrm{2\,800\,km\,s^{-1}}$. We demonstrate good agreement
between the NICER and HETGS continua, provided that one properly accounts for
the differing manners in which these instruments view the dust scattering halo
in the source's foreground. Unusually, we find a possible set of Ca lines in
the HETGS spectra (with significances ranging from 97.0% to 99.7%). We
hypothesize that IGR J17591-2342 is a neutron star low mass X-ray binary at a
distance of the Galactic bulge or beyond that may have formed from the collapse
of a white dwarf system in a rare, calcium rich Type Ib supernova explosion.
