The simulation of hypersonic plasma flow is of critical importance to the design, optimisation and construction of re-entry spacecraft. Tools for conducting such simulations must be capable of modelling various kinds of thermochemical non-equilibrium, as well as a high degree of shock resolution and high accuracy post-shock flow characteristics. The development and characterisation of a new toolkit designed for such problems is presented herein; OP2A. The OP2A toolkit is capable of dealing with the complex phenomena arising in re-entry flows and the high accuracy shock resolution required to accurately and precisely simulate post-shock flows. Additionally, OP2A is designed to facilitate the optimisation of space vehicle design through fluid simulation. It does so by prioritising rapid mesh generation and the seamless modification of physical simulation elements and models, to allow for rapid testing of various simulation configurations. In order to achieve this, emphasis has been placed upon the efficiency, flexibility and stability of OP2A, and certain numerical aspects have been chosen to facilitate rapid grid generation. OP2A can resolve simulated quantities to second order accuracy in both space and time. In addition, OP2A is able to simulate the chemistry of various gas compositions, allowing for the simulation of multiple atmospheres. This work documents the theoretical and numerical implementations within OP2A, and details the more notable computational aspects designed to facilitate spacecraft optimisation simulations. OP2A’s thermochemical modelling capabilities have been thoroughly evaluated and the results are presented herein. OP2A has also been used to simulate several results of interest to re-entry simulation, detailing the effects of thermochemical non-equilibrium upon plasma flows about a spacecraft. These results are presented and discussed in terms of their significance to re-entry problems and within the context of the surrounding literature. The direction of the future development of OP2A is also discussed, including details of both numerical and computational expansions.