Interactions between the Reaction Control System (RCS) jets and the bow shock from the aeroshell of a Mars Science Lab (MSL) model are investigated. Images are obtained experimentally at the University of Virginia using a low-density, hypersonic wind tunnel with the Planar Laser Induced Iodine Fluorescence technique. The models are .44% MSL aeroshells fitted with 0.5 mm RCS orifices to simulate Reaction Control Systems in both parallel and transverse jet directions relative to the aeroshells. Experiments are conducted at Mach 12 in the underexpanded jet freestream flowfield with sonic RCS jets. Images for both transverse and parallel jets are obtained for nozzle-thrust coefficients ranging from 0 to 3. It is found that there is much interaction between the aeroshell bow shock and the RCS jet for the transverse jet cases; however, there was not much interaction between the parallel jet and the bow shock on the aeroshell. Results from a nozzle-thrust coefficient of 0.5 were compared to numerical simulations for similar conditions obtained using CFD at the University of Michigan. It is found that there is good agreement in flowfield density between the experimental and numerical results in the jet core of the RCS but greater differences near the jet boundaries.

Due to scientific interest in increasing the mass of Mars entry systems and the altitude of their landing sites, the size requirements for the conventional aerodynamic decelerators used to slow the vehicle from hypersonic velocities in the upper atmosphere to zero velocity on the surface may become unfeasible. One option is propulsive decelerator (PD) jets which may be used to slow the vehicle down to appropriate speeds. The use of these PD jets, however, involve complex flow interactions that are still not well understood. This paper describes numerical and experimental techniques that are used in an effort to understand these interactions. The numerical simulations use a scaled version of the Mars Science Laboratory aeroshell geometry with a sonic PD jet in a single-nozzle configuration located at the center of the forebody in Mach 12 flow of iodine-seeded nitrogen gas. The boundary conditions for the PD jet are non-dimensionalized using the thrust coefficient in order to compare the numerical results with experimental data from previous and ongoing work. The results show that the flowfield features, such as the bow shock, PD jet shock, and recirculation regions in front the aeroshell's forebody, are all affected by the thrust coefficient of the PD nozzle. These effects also extend to the surface and aerodynamic properties of the aeroshell. The results show that as the thrust coefficient increases, the absolute values of the pressure and shear stress along the surface of the aeroshell decrease and approach a roughly constant value over the entire surface. The aerodynamic drag coefficient of the aeroshell also decreases and approaches an almost constant value equal to 8% of the value for the PD jet off case as the thrust coefficient increases. Finally, comparisons between the numerical results and experimental data show good agreement in the bow shock profile and standoff distance as well as the aerodynamic properties of the aeroshell between the two sets of results.

Future high-mass spacecraft entering the thin Martian atmosphere will exceed the capabilities of supersonic and subsonic parachutes and will incorporate other means of deceleration. Propulsive deceleration is one technology that is being considered. The interaction of the spacecraft aerodynamics with the propulsion deceleration jets has been shown to cause a decrease in drag coefficient with increasing thrust coefficient, which is not desirable for deceleration. Planar laser-induced iodine fluorescence images for a single-propulsion deceleration jet showed a lifting of the vehicle bow shock away from the aeroshell. Flowfield calculations showed that this lifting provided a shielding effect, preventing the freestream mass and momentum flux from reaching the aeroshell surface, creating a low-pressure region between the jet boundary and the aeroshell. With four peripheral propulsive deceleration jets, planar laserinduced fluorescence images and computational fluid dynamics calculations showed that the vehicle bow shock is maintained between the jets as the thrust coefficient is increased. This bow shock is responsible for greater drag preservation with the peripheral jets. The calculations also showed that high pressure is maintained between the peripheral jets. These results suggest that using a few peripheral propulsion-deceleration jets located near the aeroshell shoulder would provide the greatest drag preservation when using propulsive deceleration.

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The fluid interactions produced by a sonic reaction control system (RCS) thruster for a Mars-entry aeroshell are investigated using computational fluid dynamics (CFD). The study uses a scaled Mars Science Laboratory (MSL) aeroshell at a 20 • angle-of-attack in Mach 12 flow of I2-seeded N2 gas. The RCS jet is directed either parallel or transverse to the freestream flow in order to examine the effects of the thruster orientation with respect to the center of gravity of the aeroshell. The results show that both the parallel and transverse RCS jets obstruct the flow around the aeroshell and impinge on the surface, which increase the overall pressure on the aftbody. As a result, the RCS jet decreases both the drag and lift forces, and the moment acting on the aeroshell, particularly at relatively large RCS thrust conditions. The results also indicate that the fluid interactions produced by the parallel and transverse jets affect the control effectiveness of the RCS. The performance of the parallel RCS thruster is close to ideal due to relatively small aerodynamic interference induced by the jet. However, the relatively large aerodynamic interference produced by the transverse RCS jet causes a deficit of control authority. The physical accuracy of the computational method is assessed by comparing the numerical results with experimental visualizations.