High-efficiency space propulsion devices utilize ion plumes to generate thrust. Numerical models of the plume dynamics are utilized to explore design variables, to understand operating conditions, and to improve performance. In this talk, we discuss the computational challenges associated with modeling electrically charged and neutral particles in spacecraft electric propulsion devices. We will focus on the unique challenges and opportunities specific to electrospray ion plumes and our goals to connect atomic-scale dynamics to device-scale properties. Several approaches are utilized to capture physics at varying scales, including molecular dynamics, n-body, and particle-in-cell methods.