NASA Dragonfly Mission – Rotor Blade Design and Optimization

Abstract:
The objective of NASA's 4th New Frontiers Mission, Dragonfly, is to explore the surface chemistry and habitability of Saturn's largest moon, Titan. With its thick nitrogen atmosphere, liquid methane cycle, and rich, organic surface materials, Titan holds clues to prebiotic chemistry to answer fundamental scientific questions about the building blocks of life. The combination of high fluid density (4.4x) and low gravity (1/7th) compared to Earth makes exploration of this cryogenic ocean world in the outer solar system feasible by means of a relocatable lander - this is Dragonfly, a multi-rotor vehicle designed for the unique atmospheric conditions and environment at Titan. Dragonfly enables flight in a quad-rotor configuration with two counter-rotating, canted rotors mounted on each of four sting arms. All eight rotors are three-bladed, stiff metal rotors that are controlled by variable-speed electric motors. The objective of this paper is to tell the story of Dragonfly's rotor blade design and optimization, starting with the conceptual design based on flight requirements for Titan, preliminary design iterations of the rotor blades, and detailed design and optimization of the final configuration. Details are given with respect to design constraints driven by the cryogenic Titan environment, resulting from scientific instruments located on Dragonfly, and the overall mission flight profile. Design tools ranged from momentum theory to free-wake methods, hybrid computational fluid dynamics (CFD), and blade-resolved CFD analyses compared to wind tunnel measurements of rotor and lander combinations.

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