Monitoring the recession of ablative TPS during atmospheric entry of a capsule allows better understanding of ablation and its kinetics. Optimisation of capsule aerodynamics and TPS design and sizing can all benefit from knowledge of the progres-sion of TPS recession. Such knowledge helps to reduce uncertainties and increase modeling reliability especially for new environmental and entry conditions.

The presently used TPS recession sensors ARAD and HEAT both rely on the char to complete the electric circuit which means they cannot be reliable and the signal-to-noise ratio is often very low.

This ReGS sensor is a continuation of the ReWiG Phase A project (ESA 4000111843/14/NL/SC) which has proved the concept of a resistive grid sensor which does not depend on the char for circuit completion. In the new TPS recession sensor described here (patent under preparation), a thin metallic grid or mesh eliminates the dependence of the sensor on the char since the circuit remains closed as TPS recession proceeds. The voltage change across the grid now only depends on the length of the grid. If the grid is mounted through the thickness of the TPS, it will recess with the TPS and its resistance will change predictably. Further, in order to compensate for the temperature effect on the grid resistance, a thin resistance foil of identical material is mounted parallel to the grid and the nett signal due to the grid/TPS recession is therefore the difference between the two signals Vg-Vf. The REGS sensor can be built using a variety of metallic meshes or grids, even ones directly printed onto an insulating plate.

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