An open carbon-phenolic ablator for scientific exploration

Space exploration missions rely on ablative heat shields for the thermal protection of spacecraft during atmospheric entry flights. While dedicated research is needed for future missions, the scientific community has limited access to ablative materials typically used in aerospace. In this paper, we report the development of the HEFDiG Ablation-Research Laboratory Experiment Material (HARLEM), a carbon-phenolic ablator designed to supply the need for ablative materials in laboratory experiments. HARLEM is manufactured using polyacrylonitrile-based carbon fiber preforms and a simplified processing route for phenolic impregnation. We characterized the thermal protection performance of HARLEM in arcjet experiments conducted in the plasma wind tunnel PWK1 of the Institute of Space Systems at the University of Stuttgart. We assessed the performance of the new material by measuring surface recession rate and temperature using photogrammetry and thermography setups during the experiments, respectively. Our results show that HARLEM's thermal protection performance is comparable to legacy carbon-phenolic ablators that have been validated in different arcjet facilities or in-flight, as demonstrated by calculations of the effective heat of ablation and scanning electron microscopy of as-produced samples. In-house manufacturing of carbon-phenolic ablators enables the addition of embedded diagnostics to ablators, allowing for the acquisition of data on internal pressure and more sophisticated pyrolysis analysis techniques.

Novel heat flux controlled surface cooling for hypersonic flight

This paper presents a new method in theory and experiment to adjust the transpiration cooling based on the actual measured heat flux. This is particularly useful in extreme heating environments, e.g. atmospheric entry flight or combustion chamber applications. In such environments, usually cooling is set constant based on the vehicle design, yet a mass efficient and performant cooling is sought after. We present a method with real-time surface heat flux determination of the transpiration cooled wall and an automatic adjustment of the cooling. The heat flux is determined based on a system identification process. The heat flux measurement itself is derived non-intrusively from the measurement of pressure inside the plenum, i.e. the region between mass flow controller and porous wall. The particular advantage of this system is that the heat shield material is not weakened by any sensor system and its performance is optimized with respect to cooling needed at a certain heating level. Another new feature of the pressure heat flux transformation is the attenuation of a destabilizing positive feedback loop, where the transpiration cooling controller's output (i.e. mass flow rate) strongly influences its input (i.e. plenum pressure). We describe the identification of the model parameters for the heat flux determination, which are found and verified by a calibration approach. The controlled cooling was demonstrated in a hot air plasma flow with a reference heat flux of up to 1.4 MW/m[Formula: see text]. The results show the performance and verify the applicability in a real flight environment.

Two-photon induced polarization spectroscopy of xenon 7p[1/2]0

A novel experimental setup for two-photon induced polarization spectroscopy of xenon using a single dye laser is demonstrated. The experimental setup for probing this two-photon xenon transition using this technique has been developed in the High Enthalpy Flow Diagnostics Group of the Institute of Space Systems. The characterization of the setup is achieved through a polarization lineshape modelling approach accounting for absorption, dispersion, and imperfections in the alignment of the analyzing polarizer for asymmetrical polarization profiles. It is demonstrated that the lineshape modelling approach yields consistent results for measurements with pronounced asymmetrical lineshape properties as well as for those with symmetrical lineshapes. For the first time, data on pressure broadening and pressure dependent redshift of the absorption center wavelength of xenon 7p[1/2]₀ is presented. The results show a pressure broadening of 1.475 pm/bar full width at half maximum and a redshift of 0.8425 pm/bar.