Thesis (Ph. D.)--Open University. BLDSC no. DXN024724.

The main objectives of this study are to determine how various physical and chemical properties of geologic samples can be investigated by Fourier Transform InfraRed (FTIR) spectral analyses, and determine how each of these individual properties uniquely alter the mid-infrared spectrum. Of particular interest is how extraterrestrial samples differ (spectrally) from terrestrial samples, and how such findings can be applied to current and future missions to airless planetary bodies (such as Diviner Lunar Radiometer, aboard the Lunar Reconnaissance Orbiter, and the Mercury Thermal Radiometer on BepiColombo). As such, a range of geological samples have been analysed including terrestrial rocks (anorthosite, granite, grabbro etc.), mineral standards (common rock-forming minerals), lunar meteorites (from Miller Range, Antarctica), and Apollo 14, 15, and 16 soils. A new technique to analyse such samples has been developed and implemented as part of this study: FTIR spectral imaging of unconsolidated samples (powders and soils) to obtain modal mineralogy estimates. Such estimates are comparable to QEMSCAN analyses and spot point counting of the same samples. This is particularly relevant for the non-destructive analysis of Apollo soil samples (bulk and sieved fractions). Individual spectra of polished terrestrial and extraterrestrial samples have been obtained in preparation for the creation of a spectral database. Such samples also have coupled chemical composition information via Electron Probe MicroAnalysis (EPMA). To have a spectrum and an associated chemical composition for each mineral in a database is unique compared to other spectral databases. Analyses of lunar meteorites resulted in an understanding of how shock (caused by hypervelocity impacts) alters the physical and spectral properties of lunar minerals. FTIR microscopy of individual minerals and phases in the meteorites were coupled with optical and cathodoluminescence (CL) imaging to identify the level of shock obtained by each mineral and phase. The FTIR reflectance bands of plagioclase merge with increasing shock pressure until a single, low-reflectance broad peak is displayed by the most highly shocked plagioclase (>45 GPa), and a dark-red colour is present in CL images. FTIR and QEMSCAN analyses of Apollo regolith samples have provided an understanding of the spectral effects of bulk mineralogy, maturity (a measure of the time spent at the lunar surface), grain size, and mineral chemistry. Using such information, the modal mineralogy of each sample has been estimated, one of which had not previously been analysed for its modal mineralogy. Samples from the same Apollo missions present similar spectral features, meaning FTIR spectroscopy can be used to identify the origin of lunar soils. A weak correlation in maturity with a spectral feature termed the Christiansen Feature has been found for lunar samples. Related to maturity, FTIR spectra of individual agglutinates (a product of space weathering) have been obtained and the spectral properties of agglutinates (decreased %Reflectance values of the region sensitive to geological materials) resemble those of highly mature lunar soils.

Understanding the effects of various wheel parameters on tractive performance is not completely understood. In order to properly quantify the individual effects of wheel parameters on the mobility of rigid and flexible wheels in soft soil, tests were performed, in cooperation with NASA Glenn Research Center (NASA-GRC), using the terramechanics rig at the Virginia Tech Advanced Vehicle Dynamics Lab (AVDL). To conduct such a study, four different wheels were evaluated under similar normal loads, slip ratios, and soil density. The first wheel represents the baseline, against which all the others were benchmarked. The remaining three wheels included the following parameter changes: 1) same diameter as the baseline but wider, 2) same width as the baseline but smaller in diameter, and 3) same width and diameter as the baseline but with a longer contact length. For each test the normal load, drawbar pull, and driving torque were measured and recorded for further analysis. To measure the effect of the changes in the wheels' parameters on the contact patch under different loads, a pressure pad was embedded below the surface of the Lunar simulant to measure the contact patch shape, size, and pressure distribution. Analysis of the experimental results showed that the drawbar pull was more significantly affected by the wheel diameter than by the contact width, and that same trend followed suit for the driving torque. Overall, the greater contact patch area resulted in a higher drawbar pull and torque. / Master of Science

Lunar soil, defined as the finest part of the lunar regolith which covers the entire surface of the Moon, has shown to have remarkable shear strength properties, highlighted by the clearly visible effects of soil cohesion. The main objective of this thesis is to unveil the physical explanations causing this unusual soil behaviour in a waterless, airless, lunar environment. Ultra-High Vacuum (UHV), in particular, is considered responsible for increasing the strength of surface energy forces due to lunar soil outgassing. In turn, the presence of surface energy forces, arising from van der Waals intermolecular forces, is thought to alter the mechanical properties of lunar soil. A particle-based microscopic approach by means of the Discrete Element Method (DEM) was utilised to investigate the effects of surface energy forces on the macroscopic soil be- haviour. A micro-mechanical contact model, based on the JKR theory, was selected to describe the inter-granular behaviour between lunar soil particles. Physical and geometrical parameters typical of lunar soil were employed. Several triaxial tests were run to identify a link, if any, between the microscopic surface energy parameter and the macroscopic soil cohesion, which was interpreted as a true soil cohesion. In addition, very low stress levels and high soil densities were simulated in order to take into account the low gravitational field and the high state of soil compaction caused by continuous meteorite impacts on the Moon. Results from triaxial tests were analysed at both the peak and critical state. It was found that in the ideal case of perfectly spherical grains, the presence of adhesion is a source of noticeable macroscopic soil cohesion. However, no influence was observed in terms of macroscopic friction angle. Furthermore, a brittle macroscopic soil behaviour was revealed, owing to the simulated inter-granular chemical bonds and the very low stress conditions applied. Finally, similar to the behaviour of cemented sands, very little cohesion was recorded at the critical state. Subsequently, particle shape effects were investigated by complementing the numerical model with a simple form of inter-particle rolling resistance. Simulations were also run with non-convex grains of increasing geometrical complexity in order to simulate more realistically the irregular shapes of lunar soil grains. In both cases, the interplay of surface energy forces with particle shape effects resulted in even higher shear strength, with predictions similar to the estimates of shear strength for real lunar soil. Once again, the peak strength was dominated by macroscopic cohesion which, on the other hand, was hardly observable at the critical state, confirming the tendency observed from spherical grains. Finally, the practical implications of the above findings were discussed in terms of bearing capacity, trafficability and slope stability on the lunar surface. In particular an analytical approach, based on the bearing capacity problem, was devised to study the performance of a rigid wheel rotating on a lunar terrain and operating under different dynamic conditions.

No description available.

A drawbar pull (DP) test procedure was developed at the NASA Glenn Research Center (GRC) for testing and developing designs for off-road vehicles. The motivation was to develop a procedure that would produce repeatable results and could be replicated by other researchers. While developing the test methodology, it became apparent that there was a certain degree of scatter in the results among identical tests. In order to characterize the disparities, an experimental study was conducted consisting of systematically varying specific test parameters. The selected performance metric was the DP-TR (travel reduction) relation. The selected parameters were: 1) the starting terrain condition, 2) the distance traveled by the vehicle under an applied, constant DP force, and 3) the density of the prepared terrain. Respectively, these parameters were selected to observe: 1) how differences in the starting area, or "launch pad," would affect the resulting performance of a test, 2) if a steady-state region of performance exists and how does performance change with the distance traveled, and 3) the relationship between prepared terrain density and performance. These experiments were conducted in a dry, granular, cohesionless, silica based soil called the GRC-1 Lunar Soil Simulant. The results of these studies were that the variations in both the starting terrain condition and the distance traveled did not significantly affect performance. The relationship between performance and terrain density was that only in a region of low density was the TR constant; subsequently, the TR decreased steadily with increasing density. / Master of Science

Indiana University-Purdue University Indianapolis (IUPUI) / This dissertation focuses on quantification of submicroscopic iron of different sizes, mineral abundance and grain size of lunar soils using Hapke's radiative transfer model. The main objective is to explore implications of these results for assessing the relative importance of solar wind implantation versus micrometeorite impacts for lunar space weathering as well as three hypotheses (solar wind deflection, comet impact and dust transport) for swirl formation on the Moon. Results from this study can help to make connections between ordinary chondritic meteorites and asteroids, and put physical and chemical constraints on heating processes in the early solar system.