  Light curves are the primary observable of type-I x-ray bursts. Computational
x-ray burst models must match simulations to observed light curves. Most of the
error in simulated curves comes from uncertainties in $rp$ process reaction
rates, which can be reduced via precision mass measurements of
neutron-deficient isotopes in the $rp$ process path.
  We perform a precise Penning trap mass measurement of $^{27}$P utilizing the
ToF-ICR technique. We use this measurement to calculate $rp$ process reaction
rates and input these rates into an x-ray burst model to reduce simulated light
curve uncertainty. We also use the mass measurement of $^{27}$P to validate the
Isobaric Multiplet Mass Equation (IMME) for the A=27 T=$\frac{3}{2}$ isospin
quartet which $^{27}$P belongs to.
  The mass excess of $^{27}$P was measured to be -670.7(6) keV, a fourteen-fold
precision increase over the mass reported in the 2020 Atomic Mass Evaluation
(AME2020). X-ray burst light curves were produced with the MESA (Modules for
Experiments in Stellar Astrophysics) code using the new mass and associated
reaction rates. Changes in the mass of $^{27}$P seem to have minimal effect on
light curves, even in burster systems tailored to maximize impact.
  The mass of $^{27}$P does not play a significant role in x-ray burst light
curves. It is important to understand that more advanced models do not just
provide more precise results, but often qualitatively different ones. This
result brings us a step closer to extracting stellar parameters from individual
x-ray burst observations. The IMME has been validated for the $A=27, T=3/2$
quartet. The normal quadratic form of the IMME using the latest data yields a
reduced $\chi^2$ of 2.9. The cubic term required to generate an exact fit to
the latest data matches theoretical attempts to predict this term.
