*Article* **Comprehensive Comparison of Different Integrated Thermal Protection Systems with Ablative Materials for Load-Bearing Components of Reusable Launch Vehicles**

**Stefano Piacquadio 1,\*, Dominik Pridöhl 1, Nils Henkel 2, Rasmus Bergström 3, Alessandro Zamprotta 3, Athanasios Dafnis <sup>1</sup> and Kai-Uwe Schröder <sup>1</sup>**


**Abstract:** Economic viability of small launch vehicles, i.e., microlaunchers, is impaired by several factors, one of which is a higher dry to wet mass ratio as compared to conventional size launchers. Although reusability may reduce launch cost, it can drive dry and/or wet mass to unfeasibly high levels. In particular, for load-bearing components that are exposed to convective heating during the aerothermodynamic phase of the re-entry, the mass increase due to the presence of a thermal protection system (TPS) must be considered. Examples of such components are aerodynamic drag devices (ADDs), which are extended during the re-entry. These should withstand high mechanical loading, be thermally protected to avoid failure, and be reusable. Ablative materials can offer lightweight thermal protection, but they represent an add-on mass for the structure and they are rarely reusable. Similarly, TPS based on ceramic matrix composite (CMC) tiles represent an additional mass. To tackle this issue, so-called integrated thermal protection systems (ITPS) composed of CMC sandwich structures were introduced in the literature. The aim is to obtain a load-bearing structure that is at the same time the thermally protective layer. However, a comprehensive description of the real lightweight potential of such solutions compared to ablative materials with the corresponding sub-structures is, to the authors' knowledge, not yet presented. Thus, based on the design of an ADD, this work aims to holistically describe such load bearing components and to compare different TPS solutions. Both thermal and preliminary mechanical designs are discussed. Additionally, a novel concept is proposed, which is based on the use of phase change materials (PCMs) embedded within a metallic sandwich structure with an additively manufactured lattice core. Such a solution can be beneficial due to the combination of both the high specific stiffness of lattice structures and the high mass-specific thermal energy storage potential of PCMs. The study is conducted with reference to the first stage of the microlauncher analysed within the European Horizon-2020 project named Recovery and Return To Base (RRTB).

**Keywords:** reusable launch vehicle; thermal protection system; integrated thermal protection system; ablative material; ceramic matrix composite; phase change material; lattice structure; additive manufacturing
