Surface Characterization of Metallic and Ceramic TPS-Materials for Reusable Space Vehicles

Paper number

IAC-06-C2.6.09

Author

Mr. Markus Schuessler, University of Stuttgart, Germany

Coauthor

Mrs. Monika Auweter-Kurtz, Institute of Space Systems, Germany

Coauthor

Dr. Georg Herdrich, Germany

Year

2006

Abstract

Performance and lightweight design of future thermal protection systems (TPS) strongly depend on the surface properties of the material used: catalytic efficiency and total emissivity. During the re-entry of a space vehicle into the Earth’s atmosphere, the airflow molecules passing the bow shock become dissociated. The atoms then recombine on the TPS surface or in the gas phase to molecules. The different recombination rates depend on the catalytic efficiency of the material used. Due to the transfer of recombination energy to the material surface, the heat load depends on the catalytic efficiency of the TPS material. Since the catalytic properties of these materials depend on temperature, the heat flux indirectly depends on the vehicle surface temperature, and consequently on the total emissivity of the TPS material.
Due to this strong interaction between catalytic effects and total emissivity, the characterization of the involved phenomena and temperature dependent values are essential for the development of future TPS systems.   
This paper describes the methodology used to determine the recombination coefficients of metallic and ceramic TPS-materials in pure oxygen and nitrogen plasmas. The methodology is based on Goulard’s Theory and heat flux measurements in the plasma wind tunnel facilities at IRS. Additional necessary plasma parameters, e.g. stagnation enthalpy, Pitot pressure and Mach number, have been derived using the various measurement techniques, plasma probes and numerical tools developed at IRS.
In addition, a newly qualified method and test facility for determing the TPS material’s total emissivity at high temperatures is described. A material sample is mounted to a pneumatic actuator and placed in a variable black body radiator, which is then resistively heated to a selected temperature. Once the sample is in thermal equilibrium with the cavity, the material sample is shifted rapidly (isothermal) out of the black body. The apparent temperature drop observed by a pyrometer enables the total emissivity to be determined according to Stefan Bolzman´s Law.
The test conditions and results of the plasma wind tunnel testing carried out in the inductively heated plasma wind tunnel facility PWK3-IPG3 at IRS will be presented. Values for the catalytic efficiency of the metallic TPS material PM1000 and high temperature ceramics SSiC, Al2O3, Spinel, and Yt2O3 are given. Values for the total emissivity of all materials are evaluated between 750 and 1800K. The results will be discussed with special attention given to the application of PM1000 as TPS material on the European re-entry capsule EXPERT.

Abstract document

IAC-06-C2.6.09.pdf

Manuscript document

IAC-06-C2.6.09.pdf (🔒 authorized access only).

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