Abstract
There are good reasons to believe that small (< 5kg), highly manoeuvrable rotorcraft may be valuable to human explorers on Mars. They could be used for scouting, aerial photography, maintenance inspection, hoisting antenna or guy wires, locating science targets and rapid transportation of small tools or regolith samples. Low atmospheric pressures and temperatures near the Martian surface present severe challenges to the design of rotorcraft. To provide sufficient lift, even allowing for lower gravitational acceleration (3.71m/s2), rotors need to be larger and turn faster than their terrestrial counterparts, thus imposing high mechanical stresses. This, combined with poor battery efficiency at low temperatures, could impose serious restrictions on the endurance of such aircraft. Extremely fine and abrasive particulate matter would also be problematic for reliable functioning of any exposed bearings, sensors and cameras. In this paper we study the use of both conventional and modified low pressure propellers for the use in a small quadrotor at low pressures. We modelled the rotors computationally and our simulations show the need for a thrust of approximately 5N per motor for a 4kg quadrotor at Mars. Blade element theory calculations have suggested that it is possible to meet these requirements. As a baseline, conventional propeller designs were tested in a vacuum chamber down to 6 mbar. As the pressure was reduced the thrust dropped significantly from approximately 6N to 0.05N. However, the power consumption also dropped from 120W to 16W due to the much lower drag on the propeller. Tests on propellers based on our simulations also demonstrated a decrease in thrust. While this system is not yet optimised, it demonstrated only a 60% decrease in thrust which compares favourably with conventional propellers, with a 40% reduction in power consumption. This suggests that correctly optimised propellers may indeed be able to be used as propulsion for lightweight multirotor aircraft on Mars. Since our vacuum chamber tests are complicated by ground effects and limited freedom to move, we intend to drop a 4kg automated test vehicle from a balloon at 120,000 feet, where atmospheric conditions approximate those at Mars, and record performance data onboard during programmed manoeuvres. The decent of the rotorcraft could also be used to correct the results for the greater acceleration due to gravity near Earth.