Material characterization and plasma testing for an inflatable heatshield for the EARS reusable smallsat platform

The EARS project, funded under the Horizon Europe programme, aims at the development of an affordable, flexible platform that can be reused and easily produced in large numbers, targeting the low-cost SmallSat market. The EARS spacecraft is designed for Low Earth Orbit to support microgravity manufacturing and small experiments. Then, the spacecraft is planned to de-orbit, perform a controlled re-entry, and be recovered to deliver its products and results back to Earth. The EARS operations concept involves a controlled re-entry and, therefore, calls for an advanced heatshield. For that purpose, an inflatable concept has been considered. Unlike state-of-the-art rigid heatshields, an inflatable heat shield has several advantages, like a lower ballistic coefficient reducing thermal loads. The envisioned inflatable heatshield is made of two main parts: a rigid nose and a flexible thermal protection system (FTPS), which will be inflated during the re-entry. The FTPS features a multilayer structure, including an outer layer exposed to high temperatures, an insulation layer that prevents heat from reaching the internal structure, and a gas barrier to protect the inflatable core from hot gases. The current material candidates include traditional Ceramic Matrix Composite (CMC) for the rigid nose, woven Refrex 1420 for the FTPS outer layer, Sigratherm GFA5 soft graphite for the FTPS insulative layer, and Kapton for the gas barrier. Preliminary numerical analyses performed in FreeFEM++ show this combination of materials maintains the underlying structure below 70ºC, considering a constant heat flux of 275 kW/m2 for 80 s, representing the trajectory heat load. This study aims to investigate a preliminary approach for using flexible materials for heat shield applications. The test strategy consists of performing Simultaneous Thermal Analysis (STA) for specific heat capacity determination and an experimental test campaign in an Inductively Coupled Plasmatron (ICP) facility to replicate re-entry conditions. Four stagnation samples were tested, targeting both maximum and minimum heat flux values (0.27 MW/m² and 0.11 MW/m², respectively) and a low-pressure condition (15 hPa). Two configurations were tested. The first consists of one with a layer of Refrex, while the other was tested in a stacking configuration (2 layers of GFA + 1 layer of Refrex). The materials were evaluated using both intrusive and non-intrusive temperature monitoring techniques. Results showed that the stacking configuration is beneficial, and the Refrex surface remains intact but loses flexibility under the test conditions.