  We present mass excesses (ME) of neutron-rich isotopes of Ar through Fe,
obtained via TOF-$B\rho$ mass spectrometry at the National Superconducting
Cyclotron Laboratory. Our new results have significantly reduced systematic
uncertainties relative to a prior analysis, enabling the first determination of
ME for $^{58,59}{\rm Ti}$, $^{62}{\rm V}$, $^{65}{\rm Cr}$, $^{67,68}{\rm Mn}$,
and $^{69,70}{\rm Fe}$. Our results show the $N=34$ subshell weaken at Sc and
vanish at Ti, along with the absence of an $N=40$ subshell at Mn. This leads to
a cooler accreted neutron star crust, highlighting the connection between the
structure of nuclei and neutron stars.
