Investigation of the performance of a coring bit in frozen mud under Martian conditions of low temperature and pressure

摘要

A diamond-impregnated bit will be the most probable choice for Mars drilling applications. This is because it can be used to drill or cut the hardest rocks, including the most common rocks on Mars, i.e., basalt and andesite (Bandfield et al., 2000). Recent results suggest a possibility of the Martian regolith containing clay minerals (Webster and Savage, 2004; Ruff, 2003), products of chemical weathering of certain minerals such as, for example, olivine (Hoefen et al., 2003) in the presence of water. Thus, in addition to volcanic rocks, the bit might also have to drill through other geological formations, including, for example, clay-rich soils commonly known as mud. This argument supposes that the Martian drill will have no option for changing bits. Thus the question exists, whether a bit of the diamond-impregnated type can also be used successfully in frozen mud. It was found that mud exhibits three different physical conditions, depending on its temperature. The bit can effectively drill and the entire core can be successfully recovered provided that the mud is kept in the temperature region between approximately ?8°C and 0°C. Above 0°C the mud becomes sticky. Below ?8°C the mud is hard frozen and the bit cannot penetrate it successfully. Measurement of the electrical resistance of the mud directly below the bit while drilling was used together with the bit temperature to assess the physical state of the mud below the bit.