Mars Entry, Descent, and Landing

The combination of landing future higher mass systems with greater accuracy on Mars may require the use of both propulsive decelerator (PD) and reaction control system (RCS) thrusters. However, the interactions between these jets, the freestream, and the aeroshell involve complex flow phenomena that are still not well understood. In a combined study, researchers at the University of Michigan and the University of Virginia are using numerical and experimental methods to study the complex flow interactions that are generated in the use of PD and RCS jets. The research objectives are four-fold. The first objective is to design, build and install Mars Science Laboratory (MSL) based models with PD and RCS jets in a hypersonic flow facility at the University of Virginia. The second objective is to use the planar laser-induced iodine fluorescence (PLIIF) technique to measure the flowfield interactions between these PD jets, RCS jets, the aeroshell and the freestream. The third objective is to develop effective procedures for physically accurate and numerically efficient computation of the complex flow interactions that are generated in the use of these PD and RCS jets for vehicle deceleration and control during Mars entry. The fourth and final objective is to validate the computational method by direct quantitative comparisons with the experimental measurements.

Numerical simulations are performed using the general CFD code LeMANS, developed at the University of Michigan and is used to simulate hypersonic reacting flows. Figure 1(a) presents Mach number contours for an axisymmetric simulation using an MSL model with a single-nozzle sonic PD jet. The jet expands from sonic conditions at the nozzle exit to higher Mach numbers (i.e. supersonic). The flow then first decelerates from supersonic to subsonic velocities through a jet shock and then from subsonic to zero velocity at a stagnation point detached from the surface of the aeroshell. The freestream also decelerates from hypersonic to subsonic velocities through a bow shock and then to zero velocity at the same stagnation point. In the interface region (region between the bow and jet shocks where the two streams mix), the total pressures for the two streams are equal as they both flow outward between the two shocks with subsequent re-acceleration to supersonic velocities. The figure also shows a region of separated flow between the PD jet boundary, the surface of the model and the mixed outflow, with a reattachment point near the shoulder of the aeroshell. Figure 1(b) shows Mach number contours on the plane of symmetry for an MSL model at 20 deg. angle-of-attack with an RCS jet in order to illustrate the flowfield features that develop during the use of these jets. The RCS nozzle is located in the backshell and the jet exists parallel to the main freestream flow. The RCS jet expands from sonic conditions at the nozzle-exit to supersonic and hypersonic conditions downstream in the wake. The jet also disturbs most of the wake region on the windside, but does not appear to interact with the bow shock that develops around the aeroshell.

Figure 1: Flowfield features of PD (left) and RCS (right) jets for Mars entry aeroshells.

This project is funded by the National Aeronautics and Space Administration (NASA Grant NNX08AH37A).