Although it is often believed that the coldness of space is ideally suited for performing measurements at cryogenic temperatures, this must be regarded with caution for two reasons: firstly, the sensitive instrument must be completely shielded from the strong solar radiation and therefore, e.g., either be placed inside a satellite or externally on the satellite's shaded side. Secondly, any platform hosting such an experiment in space generally provides an environment close to room temperature for the accommodated equipment. To obtain cryogenic temperatures without active cooling, one must isolate the instrument from radiative and conductive heat exchange with the platform as well as possible. We perform analyses on the limits of this passive cooling method for a recently proposed experiment to observe the decoherence of quantum superpositions of massive objects. In this context, we obtain temperatures of 27 K for the optical bench and 16 K for the critical experimental volume. Our analyses and conclusions can readily be applied to similar science experiments requiring a cryogenic environment in space.

This article presents the full operational experimental capabilities of the plasma wind tunnel facilities at the Institute of Space Systems at the University of Stuttgart. The simulation of the aerothermodynamic environment experienced by vehicles entering the atmosphere of Earth is attempted using three different facilities. Utilizing the three different facilities, the recent improvements enable a unique range of flow conditions in relation to other known facilities. Recent performance optimisations are highlighted in this article. Based on the experimental conditions demonstrated a corresponding flight scenario is derived using a ground-to-flight extrapolation approach based on local mass-specific enthalpy, total pressure and boundary layer edge velocity gradient. This shows that the three facilities cover the challenging parts of the aerothermodynamics along the entry trajectory from Low Earth Orbit. Furthermore, the more challenging conditions arising during interplanetary return at altitudes above 70 km are as well covered.

No abstract

It was demonstrated recently, that in transpiration cooled environments, the plenum pressure is sensitive to the surface heat flux. The Pressure Based Non-Integer System Identification (NISIp) method was found to be useful for the identification of pressure impulse responses of such systems. Using an identified system, an unknown surface heat flux can be reconstructed by measurement of the plenum pressure and deconvolution with the found pressure impulse response. Since a heat flux measurement at transpiration cooled surfaces is of fundamental interest in many applications of high-speed vehicles and propulsion systems, this methodology is intended to be further developed towards a heat flux sensor. A review of the methodology, the experimental setup and the results of first heat flux measurements in the plasma wind tunnel PWK4 at the Institute of Space Systems, Stuttgart are presented in this paper. Surface heat flux profiles for different coolant mass flow rates have been successfully determined using plenum pressure data.

This paper presents a semi-analytical solution of the coupled differential equations for fluid and solid phase in a one-dimensional porous medium in thermal non-equilibrium. The thermal impulse response of the fluid and solid phases is used to determine the pressure loss over the thickness of the material. Experimental data obtained from surface heating of porous ZrB2 samples is compared to the theoretical model. The plenum pressure, surface temperature and backside temperature are measured using pressure sensors, thermographic imaging and thermocouple instrumentation The non-integer system identification (NISI) approach is used to obtain the thermal impulse response which is then compared with the model prediction. Plenum pressure rise and thermal impulse response of the heating experiments are used to assess the volumetric heat transfer coefficient of the sample. Good agreement is found between the simulated and experimental data for the temperature and pressure measurements. The obtained heat transfer coefficients are between 2.1 • 10 4 and 6.8 • 10 4 W m −3 K −1 for mass fluxes of 10 to 244 g m −2 s −1 .