High resolution schemes for hyperbolic conservation laws

Atomic Spectra Database

The United States has successfully landed five robotic systems on the surface of Mars. These systems all had landed mass below 0.6 metric tons (t), had landed footprints on the order of hundreds of km and landed at sites below -1 km MOLA elevation due the need to perform entry, descent and landing operations in an environment with sufficient atmospheric density. Current plans for human exploration of Mars call for the landing of 40-80 t surface elements at scientifically interesting locations within close proximity (10's of m) of pre-positioned robotic assets. This paper summarizes past successful entry, descent and landing systems and approaches being developed by the robotic Mars exploration program to increased landed performance (mass, accuracy and surface elevation). In addition, the entry, descent and landing sequence for a human exploration system will be reviewed, highlighting the technology and systems advances required.

Mars Exploration Entry, Descent, and Landing Challenges

This report documents the results of a study to address the long range, strategic planning required by NASA's Revolutionary Computational Aerosciences (RCA) program in the area of computational fluid dynamics (CFD), including future software and hardware requirements for High Performance Computing (HPC). Specifically, the "Vision 2030" CFD study is to provide a knowledge-based forecast of the future computational capabilities required for turbulent, transitional, and reacting flow simulations across a broad Mach number regime, and to lay the foundation for the development of a future framework and/or environment where physics-based, accurate predictions of complex turbulent flows, including flow separation, can be accomplished routinely and efficiently in cooperation with other physics-based simulations to enable multi-physics analysis and design. Specific technical requirements from the aerospace industrial and scientific communities were obtained to determine critical capability gaps, anticipated technical challenges, and impediments to achieving the target CFD capability in 2030. A preliminary development plan and roadmap were created to help focus investments in technology development to help achieve the CFD vision in 2030.

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CFD Vision 2030 Study: A Path to Revolutionary Computational Aerosciences

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Mars exploration entry, descent and landing challenges

Ar eview of the best-available data for calculating a complete set of binary collision integral data for the computation of the mixture transport properties (viscosity, thermal conductivity, and ordinary and thermal diffusion) of 13-species weakly ionized air is presented. Although the fidelity of the data varies, all collision integrals presented herein, except for electron-neutral interactions, are estimated to be accurate to within 25% over the temperature range of interest (300‐15,000 K) for reentry and laboratory plasmas. In addition, most of the dominant atom‐atom and atom‐ion interactions for dissociated weakly ionized air were derived from ab initio methods that are estimated to be accurate to within 10%. The accuracy and valid temperature range for electron-neutral interactions vary because of scarcity of the required cross-sectional data.

Recommended Collision Integrals for Transport Property Computations Part 1: Air Species

A review of the best-available data for calculating a complete set of binary collision integrals for the computation of the mixture transport properties (viscosity, thermal conductivity, ordinary and thermal diffusion) of 17-species weakly ionized CO 2 -N 2 mixtures is presented. The fidelity of the data varies considerably, but most of the atom-atom interactions are derived from ab initio methods that are estimated to be accurate to within 5%. The remaining important interactions between neutral species are estimated to be accurate to within about 30% over the temperature range of interest (300-20,000 K) to Mars and Venus reentry plasmas. Collision integrals for important ion-neutral interactions are computed using a modified Tang-Toennies potential and have an estimated accuracy of ±25%, whereas those between trace species are approximated via the polarization (Langevin) potential model. The accuracy and valid temperature range for electron-neutral interactions vary considerably due to scarcity of the required cross section data.

Recommended Collision Integrals for Transport Property Computations Part 2: Mars and Venus Entries

A Monte Carlo sensitivity and uncertainty analysis is performed for a laminar convective heating prediction in a moderate Mars atmospheric entry condition using a nonequilibrium reacting Navier-Stokes computational fluid dynamics code. The objectives are to isolate the rate limiting mechanisms and identify the chief sources of aeroheating uncertainty. A flux-based wall catalysis formulation is developed and used to define four different catalytic regimes that are then individually analyzed at three different trajectory points. A total of 130 input parameters are statistically varied to short list a handful of parameters that essentially control the heat flux prediction. The uncertainties in these key input parameters are estimated, and a full Monte Carlo uncertainty analysis is performed. The results obtained provide the quantitative contribution of uncertainties in key modeling parameters, such as collision integrals, wall catalysis, and reaction rates to the final heat flux uncertainty. It is found that in high and low catalytic regimes, the collision integrals (which govern the transport properties of the mixture) contribute a large portion of the uncertainty, whereas in the moderately catalytic regime the catalytic properties of the surface contribute almost all of the uncertainty.

Uncertainty Analysis of Laminar Aeroheating Predictions for Mars Entries

Aerothermodynamic design environments are presented for the Mars Science Laboratory entry capsule heatshield. The design conditions are based on Navier-Stokes flowfield simulations on shallow (maximum total heat load) and steep (maximum heat flux, shear stress, and pressure) entry trajectories from a 2009 launch. Boundary layer transition is expected prior to peak heat flux, a first for Mars entry, and the heatshield environments were defined for a fully-turbulent heat pulse. The effects of distributed surface roughness on turbulent heat flux and shear stress peaks are included using empirical correlations. Additional biases and uncertainties are based on computational model comparisons with experimental data and sensitivity studies. The peak design conditions are 197 W/sq cm for heat flux, 471 Pa for shear stress, 0.371 Earth atm for pressure, and 5477 J/sq cm for total heat load. Time-varying conditions at fixed heatshield locations were generated for thermal protection system analysis and flight instrumentation development. Finally, the aerothermodynamic effects of delaying launch until 2011 are previewed.

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Aerothermodynamic Design of the Mars Science Laboratory Heatshield

The current status of aerothermal analysis for Mars entry missions is reviewed. The aeroheating environment of all Mars missions to date has been dominated by convective heating. Two primary uncertainties in our ability to predict forebody convective heating are turbulence on a blunt lifting cone and surface catalysis in a predominantly CO2 environment. Future missions, particularly crewed vehicles, will encounter additional heating from shock-layer radiation due to a combination of larger size and faster entry velocity. Localized heating due to penetrations or other singularities on the aeroshell must also be taken into account. The physical models employed to predict these phenomena are reviewed, and key uncertainties or deficiencies inherent in these models are explored. Capabilities of existing ground test facilities to support aeroheating validation are also summarized. Engineering flight data from the Viking and Pathfinder missions, which may be useful for aerothermal model validation, are discussed, and an argument is presented for obtaining additional flight data. Examples are taken from past, present, and future Mars entry missions, including the twin Mars Exploration Rovers and the Mars Science Laboratory, scheduled for launch by NASA in 2011.

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Michael J. Wright

Papers

Recommended Collision Integrals for Transport Property Computations Part 1: Air Species

Recommended Collision Integrals for Transport Property Computations Part 2: Mars and Venus Entries

Uncertainty Analysis of Laminar Aeroheating Predictions for Mars Entries

Aerothermodynamic Design of the Mars Science Laboratory Heatshield

A Review of Aerothermal Modeling for Mars Entry Missions