Mars Entry Conditions Research Articles

Stagnation-Point Aeroheating Correlations for Mars Entry

This work details the development of new stagnation-point aeroheating engineering correlations for Mars entry vehicles. Convective and radiative heating relations were formulated over a wide range of entry conditions. These relations were based on computational fluid dynamics simulations informed by recent experimental testing and modeling enhancements. For convective heating, a relation similar to those proposed in previous works was developed that is accurate to within across the domain of relevant Mars entry conditions. For radiative heating, two different functional forms were developed: exponential and polynomial relations. Each of these relations, which represents two different levels of complexity for implementation, were able to predict the radiative heating within about . The correlations were tested by applying them to the Mars Pathfinder entry trajectory to demonstrate their applicability. These new correlations provide significant improvement over existing relations in terms of the accuracy, the domain of applicability, and the captured physics, including infrared radiation and thermochemical nonequilibrium.

State-Resolved Dissociation and Exchange Reactions in CO2 Flows.

State-resolved chemical reactions in CO2 are studied by taking into account excitation of all vibrational modes and preferential reaction mechanisms. The effect of several parameters on the reaction rate coefficients is discussed; it is shown that the nonequilibrium factor in the expression for the rate coefficients of exchange reactions is much less sensitive to the number of accounted vibrational states and model parameters than that of dissociation. On the other hand, the choice of thermal equilibrium Arrhenius law parameters is crucial for the correct prediction of rate coefficients for both reactions. Developed models are implemented to the one-dimensional boundary layer code for coupled state-to-state simulations of nonequilibrium CO2 flows under Mars entry conditions. Vibrational distributions, mixture composition, flow variables, and heat flux are studied for several kinetic schemes and different models of chemical reactions. Whereas including the exchange reactions weakly affects the flow, switching between the Park and McKenzie sets of parameters results in significant modification of the kinetic mechanisms; for the McKenzie model, recombination near the wall is a dominating reaction, whereas for the Park model, chemical reactions are frozen. Different contributions to the heat flux are evaluated and a satisfactory agreement with experiments is shown.

Numerical simulations of radiative heat effects in a plasma wind-tunnel flow under Mars entry conditions

The Mars atmosphere, consisting mainly of CO2, with a few percent of N2 and other trace gases, is of interest to future space projects. Entry into its gaseous shell is of current significant research interest. For this application, an arc jet driven plasma wind tunnel is available to simulate relevant entry conditions for the planet. Recent improvements and qualification of the test facility, enables the testing on earth of high enthalpy flows with CO2 rich compositions. In order to complement the experimental analysis, numerical simulations of the test facility running at relevant ambient pressures of 600–1000 Pa, corresponding to low altitudes, have been completed. The simulations used a density-based Navier Stokes solver and non-equilibrium chemical and thermal effects which are characteristic of these types of high enthalpy flows. Special interest is given to the radiative heat transfer mechanism. Under these high temperature conditions, radiative effects become more relevant and advanced radiation models must be used. The coupling between the Navier Stokes and radiative transfer equations favours the understanding of plasma wind tunnel flows. The radiative heat is estimated using the k-distribution spectral model, which is appropriate for non-homogeneous radiating media. The numerical results and measurements are compared in order to improve the analysis methods for Mars entry flows.

Advanced Models for Vibrational and Chemical Kinetics Applied to Mars Entry Aerothermodynamics

The paper presents a comparative study of vibrational-chemical kinetics and heat transfer in carbon dioxide flows under Mars entry conditions for two classes of models: the state-to-state and multitemperature models. The state-to-state approach treats each vibrational state of a molecule as a separate chemical species, thus providing a very detailed flow description. Reduced multitemperature models are based on nonequilibrium quasi-stationary Boltzmann distributions over vibrational energy with vibrational temperatures of different modes. Implementation of multitemperature models requires much less computational effort, making them rather attractive for engineering applications. Simulations have been performed for the upper part of the Mars Pathfinder entry trajectory. Comparisons between different models demonstrate a good agreement for the flowfield variables obtained using the state-to-state and multitemperature approaches, except some discrepancies for the species mole fractions prediction. This conclusion is encouraging for computational fluid dynamics, since it confirms that multitemperature models, while not being so much detailed as state to state, are still able to capture the main peculiarities of thermal and chemical nonequilibrium flows. The transport and thermochemical models have been validated using experimental data obtained in the NASA Hypersonic Pulse ground test facility. It is shown that both state-to-state and advanced multitemperature transport models used in the present simulations provide a better agreement for the heating predictions compared to traditional models.

Validation of CO 4th positive radiation for Mars entry

This paper presents measurements and simulations of CO 4th Positive equilibrium radiation obtained in the NASA Ames Research Center's Electric Arc Shock Tube (EAST) facility. The experiments were aimed at measuring the level of radiation encountered during conditions relevant to high-speed entry into a simulated Martian atmosphere (96% CO2: 4% N2). The facility was configured to target several ranges of nominal Mars entry conditions, of which 7.35km/s at 0.1Torr (13.3Pa), 6.2–8km/s at 0.25Torr (33Pa) and 7.1–7.8km/s at 1Torr (133Pa) are examined in this paper. The CO 4th Positive system was chosen to be the focus of this study as it accounts for a large percentage of the emitted radiation for Martian entry, and also due to the difficulties of obtaining experimental validation data due to the emission appearing in the Vacuum Ultra Violet (VUV) spectral range. The focus of this paper is to provide a comprehensive comparison between the EAST data and various CO 4th Positive databases available in the literature. The analysis endeavors to provide a better understanding of the uncertainty in the measurements and quantifies the level of agreement found between simulations and experimental data. The results of the analysis show that the magnitude of the CO 4th Positive radiative intensity is very sensitive to the flow temperature. Subsequently, simulations using thermodynamic equilibrium generally under-predict the experimental data by approximately a factor of up to 2. However, when simulations are performed using a flow temperature extracted from the black body limited portion of the CO 4th Positive spectra taken from experiment, the agreement between the EAST data and simulations is generally very good. Furthermore, comparisons of experimental data and simulations across other spectral regions provide additional support for the use of the black body temperature.

Absolute Radiation Measurement in Venus and Mars Entry Conditions

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Absolute Radiation Measurement in Venus and Mars Entry Conditions

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Numerical Simulation of Nonequilibrium Stagnation-Line CO2 Flows with Catalyzed Surface Reactions

A methodology developed at the Institute for Problems in Mechanics of Moscow is used for the analysis of the catalytic properties of thermal protection materials in a CO 2 environment. The method relies on a combination of 1) heat-transfer and pitot-pressure measurements in a subsonic plasma jet and 2) numerical flow simulations. The simulated environments are typical of Mars entry conditions. In particular, this work is focused on the finite-rate chemistry part of the flow description. The extension of numerical tools developed at the von Karman Institute, required within the methodology for the determination of catalycity properties for thermal protection system materials, has been completed for CO 2 flows. Nonequilibrium stagnation-line computations have been performed for several outer edge conditions in order to analyze the influence of the chemical models for bulk reactions. Moreover, wall surface reactions have been examined, and the importance of several recombination processes has been discussed

Flow about a planetary entry vehicle

The results of the numerical investigation of equilibrium and non-equilibrium flows in hypersonic shock layer about a non-ablating body are presented. Calculations have been performed for Earth, Venus and Mars entry conditions and for monatomic gas. Viscosity, heat-conduction, diffusion, chemical reactions and radiative energy transfer have been taken into account. Numerical solutions are obtained by means of the time-asymptotic method and implicit finite-difference schemes. The results show non-monotonous variation of the shock wave distance from the body surface and non-monotonous wall pressure and skin friction distributions for the vehicles of non-analytical shape. The significant increase of radiative heat flux along the surface of large-angle blunted bodies is discovered. Radiative cooling and boundary layer effects on convective and radiative heating are discussed. The importance of absorption in non-equilibrium electronic excitation of CO molecules is found. The necessity of higher order approximations in the transport coefficients calculation for ionized gas is demonstrated.

A method for computing the nonequilibrium radiant emission from near-equilibrium shock layers

Near equilibrium shock layers nonequilibrium radiant emission calculation, noting application to Mars entry conditions