Supersonic retropropulsion for human Mars exploration class missions: overview and CFD validation

Supersonic retropropulsion (SRP) represents the most likely means to slow down during the descent phase of the next era of Martian missions, i.e. human Mars exploration class missions. A general overview of the Entry-Descent-Landing phase (EDL) is provided, referring to past missions in order to derive their limits and understand the importance of SRP for overcoming them. The preliminary results of NASA studies for the parametrization and conceptual design of a propulsion system implementing SRP during a descent Mars phase are also presented. Among all the fields of interest concerning the application of SRP, the aerodynamic one has been studied since the 60s, representing an important topic of research and development. In order to better understand the complexity of the flowfield , due to the interaction of a bow shock and exhausting highly underexpanded jet , all the factors that contribute to the definition of this flowfield have been briefly described in their salient points. Afterwards it was demonstrated the ability through the use of a computational fluid dynamic (CFD) software to reproduce the flowfield and SRP main features, thus validating the simulation with test data and code to code validation. Once validated the simulation, it has been possible to make further analysis in the computational field, indeed realizing a simplified situation where the jet expansion conditions have been replicated directly to the nozzle exit section. The use of such simplification allows a remarkable saving in the number of computational domain points, reducing the computational cost; moreover the verification of such simulation with code-to-code comparison, opens the roads for the applications of this principle in more complex simulations. Finally , an analysis of the fundamental frequencies has been carried out to study the unsteadiness of the flowfield and how the grid resolutions affects the capture of unsteady phenomena. in conclusion all results obtained with simulations showed good agreement with experimental data and validated code data, demonstrating the ability to reproduce the complex phenomenology of SRP.