Linear pyrometer for investigations of thermal protection systems

Simulated re-entry tests of reusable thermal protection systems for spacecraft are being conducted in an arc-heated, high-enthalpy wind tunnel. The operating conditions correspond to the early phase of re-entry. Steady-state operation of the test facility allows the determination of the material's performance. One of the most important measurement parameters for re-entry simulation is the material's front surface temperature, which has to be known as accurately as possible. The surface temperature is usually measured by remote pyrometers. Since the material is heated by the radiating plasma, signal disturbances are present when measuring through the plasma. Furthermore the normal spectral emittance is subject to changes, depending on the plasma conditions. In order to avoid these drawbacks which reduce accuracy, a new kind of pyrometer for the measurement of the rear side temperature was designed, where no disturbances by the plasma occur. It is integrated in the sample support system. The temperature range is 1200-2370 K and the measuring spot is 1 mm in diameter. This article describes the design and the application of the miniaturized pyrometer in the plasma wind tunnel.