Duration: 36 months
The project aims to improve our capability to predict heat loads to re-entering spacecraft. Current design margins for ablative heat shields are exorbitantly large preventing further space exploration, as vehicles become prohibitively heavy [1,2]. To reduce uncertainty in predictive tools, experimental data is required for validation and calibration of models. One of the major sources of uncertainty is the interaction of heat shield material with the hypervelocity flowfield around a spacecraft [3,4]. This is in part due to the restricted capability of state-of-the-art wind tunnels. Impulse facilities do not provide enough test time to heat models to flight temperatures, and plasma wind tunnels do not provide full flow-similarity. To improve spacecraft design, experimental data is required that replicates hot ablating heat shield material in a hypervelocity flow. The project utilises a novel ground testing methodology to address this problem by combining a plasma wind tunnel with an impulse facility. Sub-scaled models of re-entry capsules will be manufactured from real heat shield material and will be exposed to a plasma flow [5]. Once they reach flight temperature and the ablation process sets in, they are impulsively moved into a hypervelocity flow generated by an expansion tube [6]. The ablation continues while a hypervelocity flowfield is established around the capsule, allowing the novel replication of heat shield ablation in a hypersonic flowfield. This new hybrid testing methodology can be extended to different test gases representing other planets’ atmospheres, such as Ice Giants, Mars etc. [7,8], or can be used to study other entry scenarios, such as demisable man-made objects [9]. Experimental data will include optical flow diagnostics, as well as material-probe diagnostics. These measurements improve our understanding of the chemical kinetics in these flows [10-12] and enable an improved replication of re-entry including coupled material-flow physics.
References:
[1] Laub, B. ; Venkatapathy, E. “Thermal protection system technology and facility needs for demanding future planetary missions” Proceedings of the International Workshop Planetary Probe Atmospheric Entry and Descent Trajectory Analysis and Science, 6-9 October 2003, Lisbon, Portugal. Edited by A. Wilson. ESA SP-544, Noordwijk, Netherlands: ESA Publications Division, ISBN 92-9092-855-7, 2004, p. 239 - 247
[2] Christopher O. Johnston, Alireza Mazaheri, Peter Gnoffo, Bil Kleb, and Deepak Bose “Radiative Heating Uncertainty for Hyperbolic Earth Entry, Part 1:” Flight Simulation Modeling and Uncertainty. Journal of Spacecraft and Rockets 2013 50:1, 19-38
[3] Christopher O. Johnston, Peter A. Gnoffo, and Alireza Mazaheri “Study of Ablation-Flowfield Coupling Relevant to the Orion Heatshield”, Journal of Thermophysics and Heat Transfer 2012 26:2, 213-221
[4] Hermann, T., Löhle, S., Fasoulas, S., Leyland, P., Marraffa, L. and Bouilly, J.-M. "Infuence of Ablation on Vacuum-Ultraviolet Radiation in a Plasma Wind Tunnel Flow". In: Journal of Thermophysics and Heat Transfer Vol.31, No. 3 (2017), pp. 575-585, DOI: 10.2514/1.T4936.
[5] T. Hermann E.W.K. Chang, J. Schaefer, C. Joglekar, H. Boehrk" Development of Small Scale Arc-jet Facility OPG1", AIAA Scitech, Washington DC, 2023.
[6] E.W.K. Chang, C. Joglekar, T. Hermann " Integration of Arc-jet in Impulse Facility for Hypervelocity Aerothermal Testing with Ablation", AIAA Scitech, Washington DC, 2023.
[7] J Steer, P Collen, A Glenn, C Hambidge, L Doherty, M McGilvray, S Loehle, L Walpot, “Shock radiation tests for Ice Giant entry probes including CH4 in the T6 free-piston driven wind tunnel”, Radiation of High Temperature Gases Workshop, Santa Maria, Portugal, 2022.
[8] T. Marynowski, S. Löhle, and S. Fasoulas , “Two-Photon Absorption Laser-Induced Fluorescence Investigation of CO2 Plasmas for Mars Entry” Journal of Thermophysics and Heat Transfer 2014 28:3, 394-400.
[9] Hermann, T., Löhle, S., Fasoulas, S. and Andrianatos, A. "Tomographic Optical Emission Spectroscopy of a High Enthalpy Air Plasma Flow". In: Applied Optics 55, Issue 36, 10290-10298 (2016). DOI: 10.1364/AO.55.010290.
[10] Electron Number Density Measurements in a Saturn Entry Condition. Yu Liu, Christopher M. James, Richard G. Morgan, Peter A. Jacobs, Rowan Gollan, and Timothy J. McIntyre. AIAA Journal 2022 60:3, 1303-1315.
[11] Hermann, T., Löhle, S., Wei, H., Morgan, R., Bauder, U. and Fasoulas, S. "Quantitative Emission Spectroscopy for Superorbital Re-entry in the Expansion Tube X2". In: AIAA Journal of Thermophysics and Heat Transfer Vol. 31, No. 2 (2017), pp. 257-268, DOI: 10.2514/1.T4898.
