John W. Van Norman

Thruster Plume Surface Interactions: Applications for Spacecraft Landings on Planetary Bodies

Numerical and experimental investigations of supersonic jet interactions with a flat surface at various atmospheric pressures are presented in this paper. These studies were done in assessing the landing hazards of both the NASA Mars Science Laboratory and the Phoenix Mars spacecraft. Temporal and spatial ground pressure measurements in conjunction with numerical solutions at altitudes of ∼35 nozzle exit diameters and jet expansion ratios e between 0.02 and 100 are used. This study shows that, for typical landing spacecraft engine parameters, thruster plumes exhausting into Martian environments create the largest surface pressure loads and can occur at high spacecraft altitudes in contrast to the jet interactions, which occur in terrestrial and lunar atmospheres. These differences are dependent on the stability and dynamics of the plate shock, the length of the supersonic core, and plume decay due to shear layer instability, all of which are functions of the jet expansion ratio. Theoretical, experimental,...

Aerodynamic Analysis of Next Generation Supersonic Decelerators

NASA’s Low Density Supersonic Decelerator project is developing new supersonic inflatable decelerators for application during descent into low density environments like that at Mars. The design and development of these technologies is aided by simulations and ground testing, leading up to full-scale demonstration in supersonic flight dynamics tests. The decelerators being developed are (1) a 6-meter inflatable torus called the Supersonic Inflatable Aerodynamic Decelerator-Robotic (SIAD-R) (2) an 8-meter attached isotensoid Supersonic Inflatable Aerodynamic Decelerator-Exploration (SIAD-E), and (3) a 30.5 m diameter supersonic Disksail parachute. A parachute deployment device (PDD) is also being developed to extract the parachute in a controlled manner. This paper describes the use of Computational Fluid Dynamics (CFD) to develop the aerodynamic database for SIAD-R, SIAD-E and the PDD. Modeling of fluid structure interaction for SIAD-E is also included to characterize the impact of deformation on the aerodynamics. CFD is also used to determine optimal size and placement of ram-air inlets used by SIAD-E and PDD for inflation.

Mars Lander Engine plume impingement environment of the Mars Science Laboratory

The Mars Science Laboratory (MSL) Mission will land a 900-kg rover on the surface of Mars in 2010. Four Mars Lander Engines (MLEs) will be fired during the final propulsive descent to maintain a 0.75 m/s vertical rate of descent, in support of a tethered landing approach referred to as the “Sky-Crane”. At 20 m above the surface the rover will be lowered on a bridle as it continues to descend. At touch-down, a minimum of 6.5 m of vertical separation are provided between the engines nozzle exit plane and the ground-surface below [1]. This maneuver was chosen in part to minimize the ground/soil interaction that occurs when rocket engine plumes are fired into a soil media. In spite of the 6.5 m altitude above the surface, surface impingement pressures are expected to reach in excess of 2000 Pa, a metric previously established by the Viking program to mitigate soil bearing capacity failure. Plume-ground interaction has been a concern of Lunar and Mars propulsive landings for some time, but was not an issue for the Mars Pathfinder and Mars Explorer Rover era due to their use of airbag landing systems [2][3].This was also a concern of the Phoenix lander program, which fired twelve pulsed hydrazine monopropellant thrusters for its final descent and touch-down [4]. Phoenix was concerned with plume impingement soil interaction due to its high surface impingement pressure and potential for diffused gas eruptions. Phoenix was also concerned with landing site alteration due to its lack of mobility as well as instrument and solar array contamination issues. As MSL will operate in a regime that will result in ground-soil erosion a plume-ground interaction program has been undertaken to quantify the amount of soil erosion, namely the trajectory and number flux of particulates and the contamination and erosion this can impart to sensitive instruments and thermal surface coatings.

Post-Flight Aerodynamic and Aerothermal Model Validation of a Supersonic Inflatable Aerodynamic Decelerator

NASAs Low Density Supersonic Decelerator Program is developing new technologies that will enable the landing of heavier payloads in low density environments, such as Mars. A recent flight experiment conducted high above the Hawaiian Islands has demonstrated the performance of several decelerator technologies. In particular, the deployment of the Robotic class Supersonic Inflatable Aerodynamic Decelerator (SIAD-R) was highly successful, and valuable data were collected during the test flight. This paper outlines the Computational Fluid Dynamics (CFD) analysis used to estimate the aerodynamic and aerothermal characteristics of the SIAD-R. Pre-flight and post-flight predictions are compared with the flight data, and a very good agreement in aerodynamic force and moment coefficients is observed between the CFD solutions and the reconstructed flight data.

Development of models for disk-gap-band parachutes deployed supersonically in the wake of a slender body

The Advanced Supersonic Parachute Inflation Research and Experiments (ASPIRE) project will investigate the supersonic deployment, inflation, and aerodynamics of Disk-Gap-Band (DGB) parachutes in the wake of a slender body. The parachutes will be full-scale versions of the DGBs used by the Mars Science Laboratory in 2012 and planned for NASAs Mars 2020 project and will be delivered to targeted deployment conditions representative of flight at Mars by sounding rockets launched out of NASAs Wallops Flight Facility. The parachutes will be tested in the wake of a slender payload whose diameter is approximately a sixth that of entry capsules used for Mars missions. Models of the deployment, inflation, and aerodynamic performance of the parachutes are necessary to design key aspects of the experiment, including: determining the expected loads and applicable margins on the parachute and payload; guiding sensor selection and placement; evaluating the vehicle trajectory for targeting, range safety, and recovery operations. In addition, knowledge of the differences in the behavior of the parachutes in the wake of slender and blunt bodies is required in order to interpret the results of the sounding rocket experiment and determine how they relate to expected performance behind blunt bodies at Mars. However, modeling the performance of a supersonic DGB in the wake of a slender body is challenging due to the scarcity of historical test data and modeling precedents. This paper describes the models of the aerodynamic performance of DGBs in supersonic slender-body wakes being developed for the ASPIRE sounding rocket test campaign. Development of these models is based on the four available flight tests of DGBs deployed in supersonic slender-body wakes as well as on data from past flight and wind-tunnel experiments of DGBs deployed in the wake of blunt bodies, on the reconstructed at-Mars DGB performance during past missions, and on computational fluid dynamics simulations. Simulations of the wakes of blunt and slender bodies in supersonic flow have been conducted in order to investigate the differences in the flowfields encountered by parachutes deployed in both wake types. The simulations have allowed the project to investigate the fundamental differences between the sounding rocket tests and the flight of a DGB during a Mars mission and to assess the limitations of the sounding rocket test architecture for evaluating flight performance at Mars.

Aerodynamic Models for the Low Density Supersonic Decelerator (LDSD) Test Vehicles

An overview of aerodynamic models for the Low Density Supersonic Decelerator (LDSD) Supersonic Flight Dynamics Test (SFDT) campaign test vehicle is presented, with comparisons to reconstructed flight data and discussion of model updates. The SFDT campaign objective is to test Supersonic Inflatable Aerodynamic Decelerator (SIAD) and large supersonic parachute technologies at high altitude Earth conditions relevant to entry, descent, and landing (EDL) at Mars. Nominal SIAD test conditions are attained by lifting a test vehicle (TV) to 36 km altitude with a helium balloon, then accelerating the TV to Mach 4 and 53 km altitude with a solid rocket motor. Test flights conducted in June of 2014 (SFDT-1) and 2015 (SFDT-2) each successfully delivered a 6 meter diameter decelerator (SIAD-R) to test conditions and several seconds of flight, and were successful in demonstrating the SFDT flight system concept and SIAD-R technology. Aerodynamic models and uncertainties developed for the SFDT campaign are presented, including the methods used to generate them and their implementation within an aerodynamic database (ADB) routine for flight simulations. Pre- and post-flight aerodynamic models are compared against reconstructed flight data and model changes based upon knowledge gained from the flights are discussed. The pre-flight powered phase model is shown to have a significant contribution to off-nominal SFDT trajectory lofting, while coast and SIAD phase models behaved much as predicted.