Characterization of CO2 Plasma Free Stream Conditions for Atmospheric Entry Simulation

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Eichhorn, Christoph
Herdrich, Georg
Fertig, Markus
Winter, Michael
Auweter-Kurtz, Monika
Lein, Sebastian
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Due to increased interest in future space exploration missions to Venus and Mars, e.g. ESA's ExoMars mission in the framework of the AURORA program, it is inevitable to develop adequate tools to simulate atmospheric entry in CO2 dominated environments. These tools are represented on the experimental side by plasma wind tunnel facilities capable of generating high enthalpy CO2 plasma jets. In addition numerical tools are required to predict the expected convective heat flux. Additionally, numerical tools to simulate the radiation heat flux are necessary especially for re-entry in CO2 dominated atmospheres as CO2 is known to be strongly radiating. Based on the experience in earth re-entry simulations [1, 2], enhanced simulation capabilities for CO2 entry scenarios are currently under development at IRS. Using the PWK3 facility, an inductively heated plasma wind tunnel with electrode less plasma generation, high enthalpy plasma free streams of reactive or corrosive gasses can be generated. In the past this facility has been operated for example with pure oxygen. Characterization of the oxygen plasma free stream included OES, FPI and LIF [3, 4]. Due to electrode less plasma heating which prevents impurities in the plasma, the facility is predestined for material characterization, in particular investigations of the catalytic behaviour of material samples have been performed [5]. Following the experiences gained in oxygen experiments, CO2 plasma operation points with enthalpy levels, which are characteristic for atmospheric entry missions to Venus and Mars, have been established in the facility. In the proposed paper our results of OES and FPI investigations for several high enthalpy plasma conditions at 12MJ/kg, 15MJ/kg and 21MJ/kg will be discussed. The enthalpy levels have been realized at three axial positions, at 170 mm, 140 mm and 50 mm distance from the nozzle exit of the plasma source. For each position and each measurement technique radial scans have been performed. From the FPI data translational temperatures of the heavy particle species have been derived. Calculations have been based on the measurement of the 777 nm atomic oxygen triplet. In order to create a data basis for further improvement and validation of radiation codes such as PARADE [6], which are used to simulate the radiation emitted by a plasma, a large amount of emission spectroscopic measurements have been performed. A first qualitative comparison of the measurement data from the 21MJ/kg condition with numerically created CO2 spectra has been used to identify the radiating species. Atomic oxygen and atomic carbon could clearly be identified, also there is evidence for oxygen and carbon ions. From the molecule based radiation, C2 Swan and CO 3rd Pos. as well as the CO+ 1st. Neg. systems could be identified and showed fairly good agreement with the PARADE data, whereas the CO+ Comet bTail system, which is not implemented in PARADE until now, also contributed significantly to the measured radiation and therefore is recommended to be implemented in PARADE. Within the paper the principal availability of ground test facilities to simulate atmospheric re-entry by generating high enthalpy CO2 plasma free streams will be shown. Furthermore the results from the plasma characterization using FPI and OES will be presented and a qualitative comparison of the measurement results with numerically simulated spectra will be performed. References 1.Fertig, M., Modellierung reaktiver Prozesse auf Siliziumkarbid-Oberflächen in verdünnten Nichtgleichgewichts-Luftströmungen, Dissertation, IRS, University of Stuttgart, 2006. 2. G. Herdrich, M. Auweter-Kurtz, H.L. Kurtz, New Inductively Heated Plasma Source for Reentry Simulations, also AIAA Paper 98-3022, presented on the 20th AIAA Advance Measurement and Ground Testing Conference, Albuquerque, NM, June 1998, Journal of Thermophysics and Heat Transfer, Vol. 14, No. 2, pp. 244-249, April-June 2000. 3. Löhle, S., Untersuchung von Wiedereintrittsplasmen mit Hilfe Laserinduzierter Fluoreszensmessungen, Dissertation, IRS, University of Stuttgart, 2006. 4. Winter, M., Emissionsspektroskopische Untersuchung der Umströmung von Probenkörpern in hochenthalpen Plasmaströmungen, Dissertation, IRS, University of Stuttgart, 2006. 5. Pidan, S., Auweter-Kurtz, M., Herdrich, G., Fertig, M., Recombination Coefficients and Spectral Emissivity of Silicon Carbide-Based Thermal Protection Materials, Journal of Thermophysics and Heat Transfer, Vol. 19, No. 4, pp. 566-571, Oct.-Dec- 2005. 6. Pfeiffer, B., Fertig, M., Winter, M., Auweter-Kurtz, M., PARADE - A Program to Calculate the Radiation of Atmospheric Re-Entry in Different Atmospheres, Proceedings of the First International Workshop on Radiation of High Temperature Gases in Atmospheric Entry, 8-10 October 2003, Lisbon, Portugal, p. 85-91.
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