[1] Current plans to drill boreholes in the surface of Mars suppose that diamond drill bits will be used on drilling equipment developing drilling power of 100 W or less. Such drilling produces very fine cuttings. At Martian ambient pressure, it has been shown that quite small gas flows are capable of clearing these cuttings from the hole. For example, the release of 1 L of gas compressed to 50 torr is capable of removing 25 g of cuttings from a borehole 50 mm in diameter and at least 250 mm deep. Generating such volumes of gas by compressing the Martian atmosphere would not be difficult. Alternatively, the required volume of gas could be provided by the sublimation of ice trapped in the pore spaces of soil or rock in the Martian surface. Once heated by the friction of the drill bit, the ice transforms into vapor, and blows the cuttings out of the hole. Since the cuttings are, in effect, freeze-dried, they do not choke the drill bit or hole, with the result that the drilling efficiency is much greater than under terrestrial pressures and temperatures.

[1] Future missions to Mars envision use of drills for subsurface exploration. Since the Martian atmosphere precludes the use of liquids for cuttings removal, proposed drilling machines utilize mechanical cuttings removal systems such as augers. However, an auger can substantially contribute to the total power requirements, and in the worst scenario it can choke. A number of experiments conducted under Martian pressures showed that intermittent blasts of gas at low differential pressures can effectively lift the cuttings out of the hole. A gas flushing system could be incorporated into the drill assembly for assistance in clearing the holes of rock cuttings or for redundancy in case of auger jamming. A number of variables such as the particle size distribution of the rock powder, the type of gas used, the bit and auger side clearances, the initial mass of cuttings, and the ambient pressure were investigated and found to affect the efficiency. In all tests the initial volume of gas was close to 1 L and the differential pressure was varied to achieve desired clearing efficiencies. Particles were being lifted out of the hole at a maximum speed of 6 m/s at a differential pressure of 25 torr and ambient pressure of 5 torr. Flushing tests lasted on average for 2 s. The power required to compress the thin Martian atmosphere to achieve a sufficient gas blast every minute or so at 10% efficiency was calculated to be of the order of a few watts.Citation: Zacny, Z. A., M. C. Quayle, and G. A. Cooper (2005), Enhancing cuttings removal with gas blasts while drilling on Mars,