Saltation is one of the main aeolian transport methods of sand and its physics has been studied extensively both on Mars and Earth. Most studies focused on the particle dynamics of individual particles, the determination of the saltation threshold or on describing the sediment.
This study aims to further research the effect of the aerodynamic environment, specifically the pressure and shear velocity, on the degree of preferred orientation of saltated grains in the sediment. Wind tunnel experiments at various pressures and shear velocities have shown that the fabric strength increases with increasing pressure for higher shear velocities. For lower shear velocities the same is seen at higher pressures, but at low pressures, the fabric strength is increased again. At low pressures impacting grains are thought to induce splashing, randomizing the orientation of grains in the sandbed. This effect is more pronounced at high velocities and low pressures, while at high pressures the airborne streamlining of grains while in flight has a stronger influence at higher velocities, due to the increased air density. In 70% of the experiments, the microscope images of the sediment could be used to determine the wind direction with an accuracy of 10°, if data from multiple images in the same area are combined. Individual images offer less reliable results as small-scale disturbances become more pronounced.
These findings offer a new perspective on the ongoing discussion about saltation on Mars by mapping the effects of pressure and shear velocity. Further experiments at low gravity can offer a more complete understanding of the saltation process on the red planet. In the meantime, the Object Based Image Analysis technique used in this research, offers another method of estimating the wind direction on Mars, based on microscope images taken by the rovers.

Between April 2021 and January 2024, the Ingenuity drone performed 72 flights in the Martian atmosphere. This technology demonstration paved the way for future exploration of Mars using Unmanned Aerial Vehicles (UAV). However, it is not yet clear which landforms and surface processes will benefit from this new technology.
This study therefore aims to further investigate the geomorphic features on Mars that will gain to be studied from a UAV perspective. To do so, a First Person View (FPV) drone is used to image Martian geomorphic features analogues at different ground sampling distance (GSD). Analysis of the images and comparison with current in-orbit capabilities on Mars are performed to determine the needed GSD and derive recommendations for future Mars rotorcraft missions. Analogues of ejecta blocks, gullies and patterned grounds were found and imaged within the Haughton impact crater on Devon island during the field campaign of the NASA Haughton-Mars Project (02/08/2024 to 14/08/2024).
The ejecta blocks and gullies appeared to be interesting targets for UAV studies on Mars. A GSD of 6 centimeters per pixels has been identified as an upper bound to properly observe the damage state of a boulder and distinguish its impact-related origin from other hypothesis (boulder slide remnant or glacier erratic). The gully characterization, and especially the identification of a wet origin can be performed with GSD lower than 2 centimeters per pixels. However, UAV studies of patterned grounds revealed no particular benefits since the needed GSD to identify their formation mechanism was low enough to be performed using rovers. The UAV perspective only enable the identification of smaller patterns than the one observed with satellite imagery.

This study investigates the relationship between gravity and the angle of repose (AoR) in granular materials, a key parameter in the geomorphology of planets and industrial applications. Avalanches of glass beads, volcanic sand, river sand, and their mixtures were tested in Hele-Shaw cells, in various hypergravity environments (1g to 20g). A numerical method was developed to measure the AoR, validated for experiments with 3% accuracy. The AoR displays cyclic and stable AoR trends, influenced by gravity, avalanching regimes, and material properties. This was revealed by introducing the novel "heartbeat" graphs. Results suggest a "V-shaped" AoR curve across gravity levels: high in low hypogravity, decreasing near 1g, increasing from 1g to 3g, and stabilising beyond 5g. This study highlights the Froude number as a critical unifying parameter for reconciling findings across the literature.

Rotor downwash that lifts dust from the ground, often called brownout on Earth, has long challenged safe rotorcraft operations. As flight moves from dense terrestrial air toward thin, planetary atmospheres, the physics change: the same rotor, at the same height, produces a very different near-surface flow. If the minimum conditions needed to mobilize dust grains and the effects of the dust once in motion are misjudged, landings, takeoffs, and low-altitude manoeuvrers can become unsafe, sensors can be degraded, and contamination risks can rise. Despite extensive understanding of brownout at Earth sea level, the physics of rotor-induced entrainment under reduced pressure remains poorly constrained.

This thesis addresses that gap by posing a focused objective: contribute to safer and more predictable rotorcraft operations in low-pressure environments by quantifying how the thresholds and the intensity of dust entrainment produced by rotor downwash evolve as ambient pressure is stepped from Earthlike toward Mars-like conditions. In other words, the work questions how the minimum surface shear required to start motion, and the strength of the dust once moving, change as the atmosphere thins....

Desert sand acoustic emissions are produced when a “sonic sand” is sheared locally or by a natural dune slipface avalanche, resulting in a brassy sound between 50 and 400 Hz. This type of sediment exhibits particular granulometric, shape and surface characteristics, due to the grains’ erosion and transport history, and emits sounds when the sheared grain layer vibrates in a synchronized manner, much like the membrane of a speaker. Recording such sand acoustic emissions on Mars (and perhaps other planetary environments) using rover microphones could thus become a new form of observable for scientists to estimate the surface sediment’s characteristics and history from a distance, but also the granular flow dynamics taking place. To determine whether this approach could be viable in the future, it is essential to evaluate how the Martian environment may affect sand acoustic emissions differently than on Earth. After showing that the muted Martian soundscape would likely allow rovers to detect such signals from a few tens of meters, the present thesis studies the impact of the interstitial air pressure within the sand bed on the sound emission mechanism of such sonic desert sands.

In this project, silent and sonic desert sand shear flows are induced under a range of pressure levels, from terrestrial ambient pressure to Mars-like pressure, within two separate, manually operated vacuum chamber setups: a smaller chamber shaken to create the sounds, and another longer chamber that better replicates avalanche-like sand flows. The motion applied and sound produced are measured using an accelerometer and a microphone inside the chamber. Metrics in the time and frequency domains are defined to analyse the changes in sound energy, amplitude, and frequency components produced at different pressure levels. Firstly, the silent sand tests are used to establish how the air pressure level within the experimental setup affects the regular sound of sheared sand (i.e. grains impacting one another) and more generally the sound emission of “normal” sounds, whose emission mechanisms do not depend on grain packing and synchronized motion. Then, a simplified theoretical model of how the sound pressure level (SPL) of a sound evolves with decreasing acoustic impedance, is derived and validated using the silent sand measurements performed. Finally, the sonic sand measurements are compared to the SPL model and silent sand measurement results, which are used as a baseline for nominal sound production behavior, to evaluate how the interstitial air pressure affects the amplitude and signal energy of the sheared sonic sand emissions. Furthermore, differences in the sand acoustic emissions’ frequency spectra and time duration across pressure levels provide information about the possible physical changes occurring in the granular flow dynamics of the sheared sonic sand.

In both experiments, the dominant frequency very closely follows the trend of the motion metrics used, as described in the literature, and remains very consistent across pressure levels. This suggests that the maximum sheared sonic sand layer thickness is independent of the interstitial air pressure. Then, the sonic sand emissions see an increase in the sound amplitude and signal energy related metrics from ambient pressure to 413.25 mbar, unlike the gradual decrease predicted by the SPL model and the trend of silent sand measurements with decreasing pressure. Below 413.25 mbar, the results suggest a stabilized behavior, with the acoustic metrics of the emissions following the model. Furthermore, in the avalanche-like emissions, a new frequency component slightly higher than the dominant frequency emerges as the chamber pressure decreases. These observations are evidenced in the time-domain, where the sand acoustic emissions seem to initiate earlier in the granular flow at 413.25 mbar and below, resulting in greater acoustic pressure levels being produced, compared to those at terrestrial pressure. It is hypothesized that more sheared sonic sand grains synchronize at 413.25 mbar and below (compared to terrestrial air pressure), and thus increase the amplitude of the sound wave produced. For avalanche-like flows, the new frequency component that appears with decreasing pressure level seems to suggest that the minimum sheared layer thickness threshold required to produce an emission is lowered at lower pressure, which leads to a higher frequency produced initially until the full layer forms, ultimately decreasing the frequency. Further research is required to confirm these preliminary findings and theories.

The Saturnian moon Titan has a methane-based hydrological cycle similar to the water cycle on earth. This includes lakes, fluvial drainage networks, clouds and has evidence for precipitation of methane rain. Here we explore the impact of rainfall on Titan based on an analogue laboratory approach. While the composition and structure of the Titan atmosphere and its cloud systems has been studied by the Cassini-Huygens missions, the chemical composition of rain drops remains undetermined. Recent studies have put forward the possibility of soluble nitrogen within rain drops that were earlier assumed to be purely made of methane. Based on simulations, we find a 77% - 23% distribution of methane and nitrogen. The ratio was used to develop a suitable laboratory analogue approach to study splash erosion by rain drop impacts. Using this analogue approach that involved impacting individual drops on soil sample analogues and custom-built numerical models, we find that that rain drops on Titan can redistribute soil particles at larger distances (30 - 600 mm) than Earth due to different energy transmission percentages from drop to splashed matter (15% - 50% of the drop, in comparison to water). Assuming a particle launch angle of 45◦, soil particles can reach heights of ∼10-70 mm, meaning soil splashing can create visible phenomena and proof for recent rainfall events. Such observables of Titanic rainfall can be used for more detailed surface studies by future missions, such as NASA’s Dragonfly drone.

The dark flight of the meteorite in the atmosphere complicates the estimation of the impact point on the Earth’s surface. The irregular shape of the meteorite affects the aerodynamic forces during the dark flight, which can influence the trajectory of the meteorite. This further complicates the meteorite recovery. Limited knowledge of the aerodynamic properties of meteorite is speculated as one of the major reasons for partial recovery of the meteorites. Therefore, this work experimentally investigates the meteorite aerodynamics during dark flight using a subsonic wind tunnel. The drag coefficient, free fall analysis from 10 km altitude and the rotational aspects were studied using a 3D printed meteorite model. Additionally, the results were implemented in a dark flight code to study the influence of these parameters for a hypothetical meteorite fall. This study proved that aerodynamic forces are very crucial in the meteorite dark flight and strongly influences the meteorite trajectory.

It has been shown that glacially induced decompression rates under Vatnajökull cause an increase in mantle melt and enhancement in volcanic activity. Eruptions under ice can form tuyas, that can be used to constrain past ice sheet thickness. Several mountains in the Martian South Polar Region qualify as tuyas, but their exact origin is still unknown. In this study we reconstruct a palaeo ice sheet from the height and spatial distribution of these tuyas and study glacially induced decompression rates within the Martian mantle.
In a finite element model we use the reconstructed ice sheet to constrain the surface pressure load and test different lithosphere thicknesses and linear deglaciation periods. We find a general decrease in decompression rates over depth and time. Results show that a decompression rate equal to the one induced by present-day deglaciation of Vatnajökull occurs at a lower depth inside the Martian mantle. Given that the mantle temperature is close to the solidus at this depth and magma ascent velocity is sufficiently high, mantle unloading due to ice melt could have contributed to the formation of the tuyas in the Martian South Polar Region. Our study proposes present-day deglaciation of Vatnajökull as a potential analogue for processes related to deglaciation on Mars.

The need for higher spatio-temporal resolution Earth observation increases rapidly. To fill this need, the Deployable Space Telescope (DST) project aims to make a light-weight, low-volume deployable telescope. In doing so, the achievable ground resolution is high while the cost per telescope stays low. This allows for the DST to be used in constellations, thus effectively achieving a high spatio-temporal resolution. One of the issues of this design are the relative translation and rotation of the secondary mirror due to temperature fluctuations. This thesis work focused on first finding these movements by identifying the temperature variations of the secondary mirror support structure using ESATAN TMS simulations, and subsequently designing a system to keep these movements within the allowed budgets. The end-result is a novel design in which all displacements are measured by means of 4 Displacement Measuring Interferometers and corrected by means of 4 linear piezo actuators.