Investigations of Peripheral 4-Jet Sonic and Supersonic Propulsive Deceleration Jets on a Mars Science Laboratory Aeroshell

Abstract

With the launch of Mars Science Laboratory (MSL), scheduled for 2011, Viking technology developed in the 1970's is reaching its limits for entry, descent and landing (EDL) on Mars, necessitating research and development of other technologies for decelerating high mass Mars entry systems (HMMES), such as propulsive deceleration (PD) jets. In this paper planar laser-induced iodine fluorescence is utilized to obtain qualitative flow visualization images and quantitative PD jet mole fraction images of peripheral sonic and supersonic PD jet models in Mach 12 flow and compared to CFD computations. The models are 0.22% of the MSL frontal area, with Mach 1 and Mach 2.66 jets on the frontal aeroshell of the model, oriented normal to the hypersonic flow. The interactions of PD jets with a Mach 12 freestream flow are visualized with coefficients of thrust (CT) varying from 0.5 to 3.0 in increments of 0.5. It was found that as CT increases the shock stand-off distance increases for both sonic and supersonic cases, with the supersonic distance at a CT = 3.0 being 17% greater than the sonic distance. The jet penetration distance was measured to be 50% greater for the supersonic case at a CT = 3.0. Experimental results were compared with CFD calculations of the sonic 4-jet configuration. Very good comparison was shown in the streamline patterns and jet mole fraction distributions. Using the validated CFD model, preliminary calculations showed that the drag coefficient for the 4-jet peripheral case was 3 times larger than that for the single centerline jet case at a CT of 0.5 and 6 times larger at a CT of 1.5, both with sonic exit conditions and the same total mass flow rate. The preservation of the vehicle drag was attributed to the normal bow shock between the peripheral jets which does not exist in the single centerline jet. The total axial force coefficient (sum of CT and CD) was calculated to be twice as large for the peripheral 4 sonic jets as for the single sonic centerline jet at a CT of 0.5 and 50% larger at a CT of 1.5. This result suggests that, for the same total mass flow rate and sonic exit Mach number, the propulsive deceleration performance of the peripheral 4-jet PD design will be considerably greater relative to the single centerline PD jet. This result is important for the design of PD jet decelerators for EDL for future HMMES missions.