Speaker
Description
For manned missions beyond earth orbit, the radiative heat flux is expected to represent a significant portion of the total heat flux to the capsule surface. This is due to the high entry speeds and large capsule sizes expected.[1, 2] Examples of where the radiative heat flux becomes substantial include missions to Venus [1] and Mars return to earth missions[3]. A substantial portion of this radiative heat flux occurs in the VUV portion of the spectrum.[4, 5] For Venus and Mars atmospheres, composed primarily of CO2, the CO(4+) band in the VUV represents either a significant or dominant portion of the radiative heat flux. It is therefore important to validate the radiation models used for this system and to reduce the corresponding uncertainty as much as possible. The work of Brandis et al.[6] and Cruden et al.[5] compared experimental measurements of CO(4+) radiation in the NASA EAST shock tube facility with theoretical predictions using established radiation codes. Their goal was to validate the predictive capabilities of these radiation codes. However, the models underestimated the measured radiation by a factor of 2. One potential reason for this discrepancy, among others, is that the bands responsible for CO (4+) emission have not relaxed to the equilibrium post-shock temperature.
Our goal is to address this issue. The plasma facility at laboratoire EM2C operates at atmospheric pressure and provides a plasma in chemical and thermodynamic equilibrium at approximately 7000 K. We therefore have the capability to study emission from an equilibrium plasma, with the entire chemical composition and thermodynamic state accurately described by a single temperature. We can compare the measured emission to that predicted from radiation codes to validate these codes. For the radiation calculations, we use the code SPECAIR.[7] For the experimental measurements, we use a McPherson VUV vacuum spectrometer capable of making measurements down to 120 nm. We have a preliminary comparison between experimental measurements and theoretical predictions down to 165 nm. The preliminary measurements show good agreement between the model predictions. Our goal is to extend these measurements down to 150 nm and to perform a comparison between several different models available in the literature. We also plan to study VUV emission from air plasmas in order to study the VUV NO bands in the UV/VUV regions of the spectrum.
[1] W. C. Pitts and R. M. Wakefield, "Performance of entry heat shields on Pioneer Venus Probes," Journal of Geophysical Research: Space Physics, vol. 85, no. A13, pp. 8333-8337, 2019/02/10 1980.
[2] J. H. Grinstead, M. J. Wright, D. W. Bogdanoff, and G. A. Allen, "Shock Radiation Measurements for Mars Aerocapture Radiative Heating Analysis," Journal of Thermophysics and Heat Transfer, vol. 23, no. 2, pp. 249-255, 2019/02/10 2009.
[3] C. O. Johnston, A. Mazaheri, P. Gnoffo, B. Kleb, and D. Bose, "Radiative Heating Uncertainty for Hyperbolic Earth Entry, Part 1: Flight Simulation Modeling and Uncertainty," Journal of Spacecraft and Rockets, vol. 50, no. 1, pp. 19-38, 2019/02/10 2013.
[4] A. M. Brandis et al., "Validation of CO 4th positive radiation for Mars entry," vol. 121, pp. 91-104, 2013.
[5] B. A. Cruden, D. Prabhu, and R. Martinez, "Absolute Radiation Measurement in Venus and Mars Entry Conditions," Journal of
Spacecraft and Rockets, vol. 49, no. 6, pp. 1069-1079, 2019/02/10 2012.
[6] A. M. Brandis et al., "Validation of CO 4th positive radiation for Mars entry," Journal of Quantitative Spectroscopy and Radiative
Transfer, vol. 121, pp. 91-104, 2013.
[7] C. O. Laux, T. G. Spence, C. H. Kruger, and R. N. Zare, "Optical diagnostics of atmospheric pressure air plasmas," Plasma Sources
Science and Technology, vol. 12, no. 2, pp. 125-138, 2003.
[8] K. Kirby and D. L. Cooper, "Theoretical study of low‐lying 1Σ+ and 1Π states of CO. II. Transition dipole moments, oscillator
strengths, and radiative lifetimes," The Journal of Chemical Physics, vol. 90, no. 9, pp. 4895-4902, 2019/02/10 1989.
Summary
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