Speaker
Description
Using a bio-based material such as wood for satellite structures can be an eco-friendly alternative to the traditionally used metals. The production of those metals is energy intensive and the mining of their raw materials often causes environmental damage. Moreover, the European space industry relies on imports for these materials. In contrast, wood is readily available throughout Europe. The feasibility of wood-based composites for CubeSats and especially small satellite class were previously reported by DLR Stuttgart. However, the behaviour of bio-based materials in space and their reaction to the space environment is still largely unknown. To mitigate this knowledge gap and to make use of the environmental advantages, this work looks into the manufacturing of a satellite structure panel made from acetylated radiata pine and the feasibility of the application of a coating to prevent erosion due to atomic oxygen (ATOX).
In a preceding Micro-VCM outgassing test beech and balsa wood exhibited a total mass loss (TML) of 5-6%, but their recovered mass loss was << 1 %. This indicates that the high TML is due to the moisture content of the wood. An acetylated radiata pine wood was chosen because the acetylation process lowers the moisture content of the wood and therefore lowers the TML to about 2%. Additionally, pine wood has better specific mechanical properties compared with other wood species.
Plywood is traditionally made from adhesively bonded wood veneers stacked in a 0°/90° lay-up. To find an adhesive suitable for space and for bonding wood, preliminary shear testing (ISO 6237) of a two-component epoxy and a film adhesive with different wood species was done. The two-component epoxy yielded higher shear strength and a better suitability for wood. Subsequently, this adhesive was chosen to bond the acetylated radiata pine veneers. To cure the adhesive under controlled pressure and temperature a universal testing machine, which was fitted with an oven, was utilised for the bonding process.
Small samples were milled out and first coating tests to prevent erosion due to ATOX were done. Prior to deposition, the samples underwent surface cleaning and plasma activation to remove organic contaminants and enhance surface energy, thereby improving adhesion of the subsequently deposited coatings. Aluminium oxide-based (Al₂O₃) and silica-based (SiO₂) thin films were deposited via magnetron sputtering physical vapor deposition (PVD) under optimised vacuum and gas flow conditions to achieve dense, uniform, and adherent coatings.
These are the first promising steps to producing a space suitable plywood panel for a satellite structure to reduce the environmental footprint of the space industry by making use of bio-based materials and greener technologies. A campaign is planned for testing the effects of ATOX on the wood to mitigate the knowledge gap of the behaviour of bio-based materials in space even further.
Keywords:
bio-based materials; satellite structure; wood; plywood; adhesive bonding; atomic oxygen; coatings