Stagnation-point radiative heating rate expressions are presented for use in air and an approximate Martian atmosphere consisting of 97 percent CO2 and 3 percent N2 Thermochemical equilibrium is assumed throughout The flight conditions and body dimensions that are modeled are representative of both manned and unmanned missions to Mars and return to earth Comparisons between the heating rates computed using the expressions presented here and independent computations yielded maximum differences of about 20 to 30 percent

Stagnation-point radiative heating relations for earth and Mars entries

Using the coupled ablation and radiation capability recently included in the LAURA flowfield solver, this paper investigates the influence of ablation on the shock-layer radiative heating for Earth entry. The extension of the HARA radiation model, which provides the radiation predictions in LAURA, to treat a gas consisting of the elements C, H, O, and N is discussed. It is shown that the absorption coefficient of air is increased with the introduction of the C and H elements. A simplified shock layer model is studied to show the impact of temperature, as well as the abundance of C and H, on the net absorption or emission from an ablation contaminated boundary layer. It is found that the ablation species reduce the radiative flux in the vacuum ultraviolet, through increased absorption, for all temperatures. However, in the infrared region of the spectrum, the ablation species increase the radiative flux, through strong emission, for temperatures above 3,000 K. Thus, depending on the temperature and abundance of ablation species, the contaminated boundary layer may either provide a net increase or decrease in the radiative flux reaching the wall. To assess the validity of the coupled ablation and radiation LAURA analysis, a previously analyzed Mars-return case (15.24 km/s), which contains significant ablation and radiation coupling, is studied. Exceptional agreement with previous viscous shock-layer results is obtained. A 40% decrease in the radiative flux is predicted for ablation rates equal to 20% of the free-stream mass flux. The Apollo 4 peak-heating case (10.24 km/s) is also studied. For ablation rates up to 3.4% of the free-stream mass flux, the radiative heating is reduced by up to 19%, while the convective heating is reduced by up to 87%. Good agreement with the Apollo 4 radiometer data is obtained by considering absorption in the radiometer cavity. For both the Mars return and the Apollo 4 cases, coupled radiation alone is found to reduce the radiative heating by 30 60% and the convective heating by less than 5%.

Influence of Ablation on Radiative Heating for Earth Entry

The experimental data for air radiation from ground-based experiments and from the Fire II and Apollo 4 flights have been reviewed and compared with a single prediction method. The ground-based data agree generally with the trends predicted by the present calculations, but differences of a factor of two are noted. The flight data from Fire II and Apollo 4 are in good agreement with the present calculations with differences of less than 50 percent.

Air radiation revisited

An approximate method is proposed for predicting the viscosity of partially ionized gas mixtures. This technique expresses the viscosity of a mixture in terms of the viscosities of the individual pure components, is simple in form, and does not require large computer run times or storage. Thus, the technique is suitable for use with complex flowfields and heat-transfer calculations. Results for gas mixtures which are representative of the atmospheres of Jupiter, Earth, and Venus, are presented and it is shown that the results compare favorably with detailed kinetic-theory analyses.

Viscosity of multicomponent partially ionized gas mixtures

This paper investigates the shock-layer radiative heating uncertainty for hyperbolic Earth entry, with the main focus being a Mars return. A baseline simulation approach involving the LAURA Navier–Stokes code with coupled ablation and radiation is presented, with the HARA radiation code being used for the radiation predictions. Flight cases representative of peak heatingMars or asteroid return are defined, and the strong influence of coupled ablation and radiation on their aerothermodynamic environments are shown. Structural uncertainties inherent in the baseline simulations are identified,with turbulencemodeling, precursor absorption, grid convergence, and radiation transport uncertainties combining for a 34 and 24% structural uncertainty on the radiative heating. A parametric uncertainty analysis, which assumes interval uncertainties, is presented. This analysis accounts for uncertainties in the radiation models, as well as heat of formation uncertainties in the flowfield model. Discussions and references are provided to support the uncertainty range chosen for each parameter. A parametric uncertainty of 47 and 28% is computed for the stagnation-point radiative heating for the 15 km=s Mars-return case. A breakdown of the largest individual uncertainty contributors is presented, which includes C3 Swings cross section, photoionization edge shift, and Opacity Project atomic lines. Combining the structural and parametric uncertainty components results in a total uncertainty of 81 and 52% for the Mars-return case.

K. Sutton

Papers

Fully coupled nongray radiating gas flows with ablation product effects about planetary entry bodies.