Bio-based ablative thermal protection materials for space application

Abstract

In the context of a growing bioeconomy, green renewable resources are of interest for the space industry. Because of its relatively low density, low thermal conductivity, easy handling and good ablative behaviour bio- and wood-based materials are taken into consideration for the use as a thermal protection system (TPS) material on hot structures such as the leading edges of stabilising fins, fairings, nose cones and other TPS applications. As a mandatory and thus flight critical structure of launch vehicles, these parts need to be aerodynamically effective, lightweight, stiff and heat resistant on its foremost front end, where high temperatures may arise from gas kinetic effects. In order to gain a deeper understanding and assess the applicability of modern bio- and wood-based materials, a systematic literature and patent analysis of bio- and wood-based materials in spaceflight has been conducted as a starting point for the research. To set a framework for the application of a bio-based material in space, functionality and boundary conditions have been analysed and form requirements for the development of the bio-based TPS material. Further, prototype materials with varying ingredients of natural fibres, binders and additives have been developed and characterised by a thermogravimetric analysis (TGA) to determine their general suitability as a TPS material. The materials have been additionally screened in more detail via the analyses of bulk density, thermal conductivity and specific heat capacity. Measurements under real environmental conditions in a plasma channel were carried out for further investigation and form the core of this work. With the defined requirements and results from screening tests and plasma channel tests a selection of the best-performing prototype material could be made. First impacts on launch vehicle’s design and an outlook for future research on bio-based TPS conclude this contribution.