We present the method used to estimate the cosmic-ray observations expected for that the Trans-Iron Galactic Element Recorder for the International Space Station (TIGERISS), which is designed to measure the abundances of the rare Ultra-Heavy Galactic Cosmic Rays (UHCR) $_{30}$Zn and heavier. TIGERISS uses planes of crossed silicon strip detectors at the top and bottom for charge and trajectory determination and acrylic and aerogel Cherenkov detectors for velocity and charge determination. Instruments are modeled in configurations for the Japanese Experiment Module (JEM) "Kibo" Exposed Facility ($\sim$1.66 m$^2$ sr), as an European Space Agency Columbus Laboratory external payload ($\sim$1.16 m$^2$ sr), and as an ExPRESS Logistics Carrier (ELC) experiment ($\sim$1.10 m$^2$ sr). Differential geometry factors determined for detector orientations within the geomagnetic field over the ISS 51.6$^\circ$ inclination orbit are used to determine geomagnetic screening. Energy spectra are integrated using the higher of the energies needed to trigger the instrument or penetrate the geomagnetic field for time-weighted bins of geomagnetic latitude, instrument orientation, and incidence angle. Finally, abundances are reduced by the fraction of events calculated to fragment in the instrument.