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The computational technique and uncertainty analysis presented in Part 1 (Johnston et al., "Assessment of Radiative Heating Uncertainty for Hyperbolic Earth Entry Part 1: Flight Simulation Modeling and Uncertainty," Journal of Spacecraft and Rockets, Vol. 50, No. 1, 2013, pp. 19-38.) for Mars-return radiative heating simulations are applied to 1960s era shock-tube and constricted-arc experimental cases. It is shown that these experiments contain shock-layer temperatures and radiative flux values relevant to the Mars-return cases of present interest. Comparisons between the predictions and measurements, accounting for the uncertainty in both, are made for a range of experiments. A measure of comparison quality is defined, which consists of the percent overlap of the predicted uncertainty bar with the corresponding measurement uncertainty bar. For nearly all cases, this percent overlap is greater than zero, and for most of the higher temperature eases (T > 13, 000 K), it is greater than 50%. These favorable comparisons provide evidence that the baseline computational technique and uncertainty analysis presented in Part 1 are adequate for Mars-return simulations. [ABSTRACT FROM AUTHOR]

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 carbon, hydrogen, oxygen, and nitrogen is discussed. It is shown that the absorption coefficient of air is increased with the introduction of the carbon and hydrogen elements. A simplified shock-layer model is studied to show the impact of temperature, as well as the abundance of carbon and hydrogen, 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 3000 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 freestream mass flux. The Apollo 4 peak-heating case (10.24 km/s) is also studied. For ablation rates up to 3.4% of the freestream mass flux, the radiative heating is reduced by up to 19%, whereas 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%. [ABSTRACT FROM AUTHOR]

This paper presents a detailed analysis of the shock-layer radiative heating to the Fire II vehicle using a new air-radiation model and a viscous shock-layer flowfield model. This new air-radiation model contains the most up-to-date properties for modeling the atomic-line, atomic photoionization, molecular band, and non-Boltzmann processes. The applied viscous shock-layer flowfield analysis contains the same thermophysical properties and nonequilibrium models as the LAURA Navier-Stokes code. Radiation-flowfield coupling, or radiation cooling, is accounted for in detail in this study. It is shown to reduce the radiative heating by about 30% for the peak radiative heating points, although reducing the convective heating only slightly. A detailed review of past Fire II radiative heating studies is presented. It is observed that the scatter in the radiation predicted by these past studies is mostly a result of the different flowfield chemistry models and the treatment of the electronic state populations. The present predictions provide, on average throughout the trajectory, a better comparison with Fire II flight data than any previous study. The magnitude of the vacuum ultraviolet contribution to the radiative flux is estimated from the calorimeter measurements. This is achieved using the radiometer measurements and the predicted convective heating. The vacuum ultraviolet radiation predicted by the present model agrees well with the vacuum ultraviolet contribution inferred from the Fire II calorimeter measurement, although only when radiation-flowfield coupling is accounted for. [ABSTRACT FROM AUTHOR]

This paper investigates the non-Boltzmann modeling of the radiating atomic and molecular electronic states present in lunar-return shock layers. The master equation is derived for a general atom or molecule while accounting for a variety of excitation and deexcitation mechanisms. A new set of electronic-impact excitation rates is compiled for N, O, and N2+, which are the main radiating species for most lunar-return shock layers. Based on these new rates, a novel approach of curve-fitting the non-Boltzmann populations of the radiating atomic and molecular states is developed. This new approach provides a simple and accurate method for calculating the atomic and molecular non-Boltzmann populations while avoiding the matrix inversion procedure required for the detailed solution of the master equation. The radiative-flux values predicted by the present detailed non-Boltzmann model and the approximate curve-fitting approach are shown to agree within 5% for the Fire II 1634-s case. [ABSTRACT FROM AUTHOR]

A new air-radiation model is presented for the calculation of the radiative flux from lunar-return shock layers. For modeling atomic lines, the data from a variety of theoretical and experimental sources are compiled and reviewed. A line model is chosen that consists of oscillator strengths from the National Institute of Standards and Technology database and the Opacity Project (for many lines not listed by the National Institute of Standards and Technology), as well as Stark broadening widths obtained from the average of available values. Uncertainties for the oscillator strengths and Stark broadening widths are conservatively chosen from the reviewed data, and for the oscillator strengths, the chosen uncertainties are found to be larger than those listed in the National Institute of Standards and Technology database. This new atomic line model is compared with previous models for equilibrium constant-property layers chosen to approximately represent a lunar-return shock layer. It is found that the new model increases the emission resulting from the 1-6-eV spectral range by up to 50 %. This increase is due to both the increase in oscillator strengths for some important lines and to the addition of lines from the Opacity Project, which are not commonly treated in shock-layer radiation predictions. Detailed theoretical atomic bound--free cross sections obtained from the Opacity Project's TOPbase are applied for nitrogen and oxygen. An efficient method of treating these detailed cross sections is presented. The emission from negative ions is considered and shown to contribute up to 10% to the total radiative flux. The modeling of the molecular-band systems using the smeared-rotational-band approach is reviewed. The validity of the smeared-rotational-band approach for both emitting and absorbing-band systems is shown through comparisons with the computationally intensive line-by -line approach. The absorbing-band systems are shown to reduce the radiative flux by up to 10%, whereas the emitting-band systems are shown to contribute less than a 5% increase in the flux. The combined models chosen for the atomic line, atomic bound--free, negative-ion, and molecular-band components result in a computationally efficient model that is ideal for coupled solutions with a Navier--Stokes flowfield. It is recommended that the notable increases shown, relative to previous models, for the atomic line and negative-ion continuum should be included in future radiation predictions for lunar-return vehicles. [ABSTRACT FROM AUTHOR]

The radiative heating environment for the Huygens probe near peak heating conditions for Titan entry is investigated in this paper. The task of calculating the radiation-coupled flowfield, accounting for non-Boltzmann and non-optically thin radiation, is simplified to a rapid yet accurate calculation. This is achieved by using the viscousshock-layer technique for the stagnation-line flowfield calculation and a modified smeared-rotational band model for the radiation calculation. These two methods provide a computationally efficient alternative to a Navier-Stokes flowfield and line-by-line radiation calculation. The results of the viscous-shock-layer technique are shown to provide an excellent comparison with the Navier-Stokes results of previous studies. It is shown that a conventional smeared-rotational band approach is inadequate for the partially optically thick conditions present in the Huygens shock layer around the peak heating trajectory points. A simple modification is proposed to the smeared-rotational band model that improves its accuracy in these partially optically thick conditions. This modified approach, referred to as the smeared-rotational band corrected, is compared throughout this study with a detailed line-by-line calculation and is shown to compare within 5 % in all cases. The smeared-rotational band corrected method requires many orders-of-magnitude less computational time than the line-by-line method, which makes it ideal for coupling to the flowfield. The application of a collisional-radiative model for determining the population of the CN electronic states, which govern the radiation for Huygens entry, is discussed and applied. The nonlocal absorption term in the collisionalradiative model is formulated in terms of an escape factor, which is then curve-fit with temperature. Although the curve fit is an approximation, it is shown to compare well with the exact escape factor calculation, which requires a computationally intensive iteration procedure. [ABSTRACT FROM AUTHOR]

A methodology to correlate flight aeroheating environments to the arc-jet environment is presented. For a desired hot-wall flight beating rate, the methodology provides the arc-jet bulk enthalpy for the corresponding cold-wall heating rate. A series of analyses were conducted to examine the effects of the test sample model holder geometry to the overall performance of the test sample. The analyses were compared with arc-jet test samples, and challenges and issues are presented. The transient flight environment was calculated for the Hypersonic Inflatable Aerodynamic Decelerator Earth Atmospheric Reentry Test vehicle, which is a planned demonstration vehicle using a large inflatable, flexible thermal protection system to reenter the Earth's atmosphere from the International Space Station. A series of correlations were developed to define the relevant arc-jet test environment to properly approximate the vehicle flight environment. The computed arc-jet environments were compared with the measured arc-jet values to define the uncertainty of the correlated environment. The results show that, for a given flight surface heat flux and a fully catalytic thermal protection system, the flight-relevant arc-jet heat flux increases with the arc-jet bulk enthalpy, while for a noncatalytic thermal protection system, the arc-jet heat flux decreases with the bulk enthalpy. [ABSTRACT FROM AUTHOR]