Aerothermal Database for Off-Nominal Earth Reentry of the Dragonfly Aeroshell

Introduction: Dragonfly is an upcoming New Frontiers mission that will send a rotorcraft to Saturn’s largest moon Titan. The mission goal is to collect data on Titan’s unique prebiotic chemistry and search for chemical bio signatures at dozens of sites on the moon’s surface [1].The rotorcraft is expected to be powered by a multi-mission radioisotope thermoelectric generator (MMRTG), which is a mission-enabling technology for Dragonfly due to Titan’s dense atmosphere and distance from the sun [2]. Radioisotope power systems have been used on many previous planetary missions (e.g. Cassini, Mars Science Laboratory (MSL), Mars 2020), and United States policy requires a safety analysis report for each mission using such a system to investigate the risks associated with launching a nuclear power source [3].The MMRTG planned for use on Dragonfly is similar to the device used for Mars 2020[4], and thus many aspects of the Mars 2020 safety analysis will be reused and adapted for Dragonfly. The safety analysis involves assessing mission failure likelihood and subsequent radiological material exposure risk at multiple points along the mission time lime to inform radioisotope contingency planning, accounting for both launch failures and accidental Earth re-entries. These off-nominal entries present several unique challenges not normally seen in classic mission design, such as the possibility of capsule tumbling during the heat pulse. The Dragonfly aerothermal team is therefore assembling a novel data-base of hypersonic computational fluid dynamics (CFD) solutions designed to predict aeroshell integrity for off-nominal Earth re-entries and help determine mission risk in the event of a launch failure.