Understanding the flow of heat at surfaces and interfaces is critical to the knowledge of thermomechanical considerations and design envelopes of spacecraft and aerospace systems. This prospectus contributes to the body of knowledge of heat transfer modeling within such systems by presenting new methodology and preliminary results on the topics of thermal conductance at a ball bearing interface, and of thermionic cooling and heat spreading at the surface of a hypersonic leading edge. Motivating Chapter 2, ball bearings are commonly used to reduce the friction in rotating mechanical components. The present work reports improved numerical approaches to model bearing thermal conductance in the absence of convection. We start by modeling the thermal pathway across a single ball-to-race pathway for a simplified geometry, an azimuthally symmetric ball in contact with a flat surface (ball-on-flat). A first-principles approach is used to calculate the static lubricant meniscus shape using a custom-developed Python code. We apply the finite element method (FEM) to extract total thermal conductance of the lubricated ball-on-flat system. Using similar methods, we also present a three-dimensional numerical model of the lubricant meniscus in a static angular contact ball bearing section (ball-on-race). By generating thermal conductance correlations for Yovanovich's classic lubricated model, our two-dimensional multiphysics model, and our three-dimensional multiphysics model, we enable comparison of the results of all three models. To compare them, parametric studies are conducted to illustrate the effect of lubricant volume and applied load on the total thermal conductance for each model. The hierarchical methodology reported here improves both the fidelity of tribo-thermo-mechanical modeling and establishes a reference for the accuracy of commonly used geometric approximations for thermal transport in spacecraft ball bearings.Motivating Chapters 3-5, leading edges of hypersonic vehicles can reach temperatures greater than 2000 °C, and radii of curvature smaller than 1 cm, at which thermionic emission (also known as electron transpiration) can play a significant role in cooling the leading edge alongside other heat transfer modes such as convection and radiation. Existing theoretical analyses of thermionic cooling with space-charge effects at a leading edge are limited to one-dimensional (1D), analytical and numerical models that do not capture the influences of geometric curvature of the leading edge or temperature gradients along the leading edge. In Chapter 3, we suggest that the key to understanding space-charge effects is development of the plasma sheath potential, and to that end we demonstrate a generalized methodology to calculate the sheath potential space in 1D Cartesian, cylindrical, and spherical coordinate systems. We extend Takamura's approach beyond the Cartesian system, and motivate sheath formation conditions for potential sheathes with and without a virtual cathode similar in nature to how Bohm originally presented his criterion of minimum Mach number for a valid 1D Cartesian sheath. By observing which parameter inputs satisfy the sheath formation conditions, we illustrate parameter spaces of minimum Mach number, potential derivative at the wall, and net current, for each coordinate system and for two different input work functions; we also show example potential spaces for each coordinate system. With our numerical approach, generalized to multiple coordinate systems, we enable computationally efficient and higher fidelity analysis of thermionic emission with space-charge effects for more realistic system geometries. In Chapter 4, because the contribution to thermionic cooling by photoexcited electrons remains relatively unexplored, we present a numerical model of thermionic and photoemission driven cooling and heat spreading, examining the movement of electrons emitted based on a random energy model within a prescribed potential space. By simulating surfaces with two different temperature gradients and imposing potential spaces derived for Cartesian, cylindrical, and spherical coordinate systems, we demonstrate that heat spreading can be significant for temperature gradients on a length scale comparable to the mean electron spreading distance. Additionally, by testing two different leading edge radii, we find that heat spreading affects a larger percentage of surface area for a smaller leading edge radius. Lastly in Chapter 5, we develop a three-dimensional particle-in-cell (PIC) based framework and propose a method to quantify the potential heat-spreading and net cooling due to space-charge limited thermionic emission at a semicylindrical leading edge. The framework has two overarching model components: an electrostatic PIC model that applies outside the leading edge surface, and a heat conduction model that applies inside the leading edge. Utilizing this framework we can assess the effect of heat spreading due to charge movement along the leading edge on the thermionic heat fluxes and resulting temperatures. We propose three different cases of code variations: thermionic cooling without any charge reflection possible, thermionic cooling and heat spreading due to charge movement and reflection enabled, and finally thermionic cooling without heat spreading. Through evaluation of these cases, we seek to quantify the ability of heat spreading to reduce leading edge temperatures and its dependence on geometry and non-thermionic heat flux gradient, advancing the analysis of thermionic cooling beyond the limits of existing one-dimensional approaches.