Protection of Lunar Structures from Micrometeoroid Strikes: Behaviour of Composite and Metallic-based Multi-layer Panels

• Experimental tests of stuffed Whipple shield and multi-shock shield • Relationship between micrometeoroid and projectile energy of a single-stage gun • Inclusion of silica, basalt, glass and Kevlar FRP and PU foam in panels • Systematic SWS vs MSS comparison under matched energy and multi-modal diagnostics • Proposal for a preferred panel configuration The application of panels to the external surface of lunar structures can offer protection from micrometeoroid strikes to the underlying structure. Inspiration for the panel design can be drawn from derivatives of the Whipple Shield as used on spacecraft and the International Space Station (ISS). This paper reports the details on an experimental study on the impact performance of two types of potential lunar structure shielding systems, namely stuffed Whipple shield and multi-shock shield. The goals of the panel testing were (i) substituting high-grade materials (as originally used in the ISS, for example) with alternative materials, such as basalt fibres, glass fibres, silica fibres, and polyurethane foam, (ii) minimise damage and debris contamination to the panel internal environment due to projectile impact, (iii) non-perforation of the panel inner wall in order to ensure the integrity of the underlying structure, and (iv) verify existing ballistic limit equations for application to panel designed using a range of materials. The impact condition investigated was based on a representative micrometeoroid of density of 0.2 g/cm 3 and speed 72 km/s, that produces a corresponding impact energy of 2200 J. The panels were in turn tested using a single-stage gas gun with velocities ranging from 612 m/s to 790 m/s, with a steel sphere of 12 mm diameter which provides the same impact energy as the representative micrometeoroid. The test results, enabled by high-speed camera images, provide a detailed understanding of the performance and failure modes of the tested panels. The best performing panel was a Stuffed Whipple Shield compromised of external layers of aluminium sheet, with an inner layer of silica and basalt fibre-reinforced polymer (FRP) composite plates. The panels were also filled with polyurethane foam. The detailed results reported in the paper can be used for informing the design of future experimental testing as well as numerical modelling.