Parametric Study of Peripheral Nozzle Configurations for Supersonic Retropropulsion

Field, CA, 94035 With sample-return and manned missions on the horizon for Mars exploration, the ability to decelerate high-mass systems to the planet’s surface has become a research priority. This paper explores the use of supersonic retropropulsion, the application of jets facing into the freestream, as a means of achieving drag augmentation. Numerical studies of retropropulsion ows were conducted using a Cartesian Euler solver with adjoint-driven mesh renement. After rst validating this simulation tool with existing experimental data, a series of three broad parametric studies comprising 181 total runs was conducted using tri- and quad-nozzle capsule congurations. These studies chronicle the eects of nozzle location, orientation, and jet strength over Mach numbers from 2 to 8 and angles of attack ranging from 5 to 10 . Although many simulations in these studies actually produced negative drag augmentation, some simulations displayed local overpressures 60% higher than that possible behind a normal shock and produced drag augmentation on the order of 20%. Examination of these cases leads to the development of an aerodynamic model for drag augmentation in which the retrojets are viewed as oblique shock generators. Flow approaching the capsule face is decelerated and compressed by multiple oblique shocks. By avoiding the massive stagnation pressure losses associated with the bow shock in typical entry systems, this approach achieves signicant overpressure on the capsule face and strong drag amplication. With a fundamental physical mechanism for drag augmentation identied, follow-on studies are planned to exploit this feature and to understand its impact on potential entry trajectories and delivered mass limits for future Mars missions.