Lunar ground motions

Lunar ground motions can potentially become a hazard for structures or infrastructures on the Moon. Therefore, within this research theme we aspire to: (a) collect  seismological recordings from the Moon which are publicly available; (b) identify usable ground motion recordings resulting from the two most pertinent types of lunar events (shallow moonquakes and meteorite impacts), and develop appropriate input motions for numerical analyses and experiments; (c) create a public online database of processed data for access by future designers, hosted on this website.

Future aspirations associated with this area are to facilitate the study of seismic hazard on the Moon, and potentially on Mars, depending on the data received from the InSight mission.

Optimisation of the structural form of arches against gravitational and inertial loading

For spanning long and within the ISRU framework (use of regoltih as a structural material), we have decided that the most ideal structural type to use is arches (in 2D) of different geometries (circular, parabolic, catenary, etc). Arches are known to rely mainly on compressive forces and through their thrust lines to convey the external loading to their supports/foundation/springing.

Self-weight and compression provide their inherent lateral stability as well. Hence, due to low gravity (on the Moon almost 1/6 of the Earth’s gravitational field), this stability is not there anymore resulting to a requirement for arches with great wall thickness. The idea to use both rigorous engineering principles and AI algorithms in order to optimise the structural form of arches in order to be able to withstand inertial loading becomes more than evident.

Static behaviour and efficiency of optimised arches against gravitational and inertial loading

Following theme 2, as structural engineers, we need to structurally assess the results from our form-finding algorithms in order to further enhance the optimal forms of the arches by looking at their static behaviour against gravitational and lateral loading. The main objective here is to minimise the principal tensile and compressive stresses by improving the structural geometry accordingly. It is observed that by increasing the cross sectional areas only at specific locations (based on the stress concentrations), the shape can be dramatically more efficient.

Dynamic behaviour and further optimisation of arches in low gravity subjected to lunar strong ground motions

The optimal constant- and varying-thickness arches (CTAs and VTAs) identified from themes 2 and 3, are further investigated through their dynamic behaviour. The scope of this theme is to develop ways to minimise bending (and therefore tension) by assuming that the regolith-based structural material has a low tensile strength. There are mainly three configurations investigated herein: (a) fixed arches; (b) arches fixed on a foundation base that is able to slide; (c) arches fixed on a foundation base that is able to uplift and start rocking, subjected to a dataset of strong ground motions as determined from theme 1. The main objective is to estimate the probability of failure of these configurations in low gravity and select the most appropriate.

Centrifuge testing of clay 3D-printed form-found arches subjected to lunar strong ground motions

Under this theme, we aspire to study the real dynamic behaviour of reduced-scale, clay 3D-printed replicas of the three configurations of theme 4 in low-gravity conditions. The reduced-scale models will fit a centrifuge box (400x750x334) that will spin with a reduced acceleration in order to simulate appropriately the corresponding gravitational fields.

Simultaneously to the spinning, the box will be shaken with the given input strong ground motions. An additional parameter of investigation is how soil-structure interaction can affect the dynamic behaviour of the arches/vaults.

Macroscopic investigation of the mechanical properties of compacted and thermally-treated martian regolith simulant (MMS1 and MMS2).

The research under this theme complements ideally the work done in other themes, as we target to macroscopically determine the mechanical properties of compacted martian regolith simulant (MMS1 and MMS2) treated thermally. The study will involve also any anisotropic behaviour of MMS1 and MMS2 bricks in flexure.