This paper presents a numerical simulation of a directional solidification experiment, which was conducted in microgravity conditions in the Material Science Lab (MSL) onboard the International Space Station. Solidification of an Al-7wt.%Si alloy in the Low Gradient Furnace (LGF) was investigated. The LGF is a Bridgman-type furnace insert for the MSL, consisting of two heated cavities separated by an insulated adiabatic zone. The simulation results include the prediction of Columnar to Equiaxed Transition (CET) and average as-cast equiaxed grain diameters. A front tracking algorithm was employed to track the growing columnar dendrite front while a volume averaging method was used to model equiaxed nucleation, growth and impingement. The thermal boundary conditions for the simulation domain were defined and computed via temperature readings that were recorded during the experiment. The experimental data were obtained from a number of thermocouples that were attached to the crucible of the sample cartridge assembly. To conclude, the microgravity experimental results and the model simulation results, including the CET, are compared.