Supersonic retro-propulsion experimental design for computational fluid dynamics model validation

The development of supersonic retro-propulsion, an enabling technology for heavy payload exploration missions to Mars, is the primary focus for the present paper. A new experimental model, intended to provide computational fluid dynamics model validation data, was recently designed for the Langley Research Center Unitary Plan Wind Tunnel Test Section 2. Pre-test computations were instrumental for sizing and refining the model, over the Mach number range of 2.4 to 4.6, such that tunnel blockage and internal flow separation issues would be minimized. A 5-in diameter 70-deg sphere-cone forebody, which accommodates up to four 4:1 area ratio nozzles, followed by a 10-in long cylindrical aftbody was developed for this study based on the computational results. The model was designed to allow for a large number of surface pressure measurements on the forebody and aftbody. Supplemental data included high-speed Schlieren video and internal pressures and temperatures. The run matrix was developed to allow for the quantification of various sources of experimental uncertainty, such as random errors due to run-to-run variations and bias errors due to flow field or model misalignments. Some preliminary results and observations from the test are presented, although detailed analyses of the data and uncertainties are still on going.

1. Introduction

Present capability for entry, descent, and landing (EDL) of small robotic missions to Mars, typified by a landed mass less than a metric ton, is predicated on the use of parachutes for a significant portion of the deceleration required to safely reach the surface. Practically speaking, this approach is not scalable to larger payloads due to physical limits with parachute size, materials, and testing capabilities. A proposed alternate approach is to use propulsive deceleration early in the trajectory, even during supersonic flight (instead of just at the terminal-landing phase). Thus, supersonic retro-propulsion (SRP), or the use of engine thrust directed into the oncoming supersonic freestream flow, is deemed a potentially enabling technology for future large payload missions to Mars. For a manned mission to Mars, the payload would be on the order of 10s of metric tons. SRP is currently one of the focus areas of the EDL project. For further discussions of SRP from a systems analysis and performance perspective, see [1] – [5]. A broader survey of the literature is provided in [6].