  It is now possible to model thermal relaxation of neutron stars after bouts
of accretion during which the star is heated out of equilibrium by nuclear
reactions in its crust. Major uncertainties in these models can be encapsulated
in modest variations of a handful of fudge parameters that change the crustal
thermal conductivity, specific heat, and heating rates. Observations of thermal
relaxation constrain these fudge parameters and allow us to predict longer term
variability in terms of the neutron star core temperature. We demonstrate this
explicitly by modeling ongoing thermal relaxation in the neutron star XTE
J1701-462. Its future cooling, over the next 5 to 30 years, is strongly
constrained and depends mostly on its core temperature, uncertainties in crust
physics having essentially been pinned down by fitting to the first three years
of observations.
