This research addresses scientific understanding and methods for mitigation of rocket nozzle erosion by solid-propellant combustion products in order to substantially increase the operating pressures of future missiles. Several processes can affect the nozzle erosion rate at high-pressure and high-temperature conditions. To characterize the nozzle erosion processes at both traditional operating pressures and at substantially increased pressure levels, two separate test facilities have been planned for operation at chamber pressures up to 8000 psi (55.2 MPa). The focus of this paper is the design and development of one of these test rigs, the rocket motor simulator (RMS). The RMS is a gaseous reactant combustor used to simulate propellent product species generated from a selected non-metallized Propellent S. Utilizing a bi-directional counter-flow vortex combustion chamber, the gaseous reactants are mixed and combusted producing a gaseous mixture with temperature and concentrations of selected oxidizing species similar to those of Propellent S. The ability to control the product species concentrations through gaseous reactant flow rates allows the evaluation of the effect individual chemical species have on the nozzle erosion process. As a means of mitigating erosion of the nozzle throat, a nozzle boundary-layer control system is also adopted in the nozzle assembly design to evaluate the methodology of boundary-layer cooling as a means of controlling erosion rates. Instantaneous erosion rates will be measured using a real-time X-ray radiography system in combination with the X-ray translucent nozzle assembly.