The Dragonfly Mission: contamination transport during entry and descent of Titan

The transport of water vapor within the Dragonfly spacecraft aeroshell was modeled to predict the contamination residing on sensitive surfaces after entry and descent through Titan's atmosphere. A lumped-parameter model based on the unsteady compressible form of the Euler equation was derived to predict the mass flux ingested and vented from the aeroshell over a wide parameter space. A nominal entry and descent profile was used to define the time-varying aeroshell vent exit boundary condition. Flow expansion through the vent was modeled as either an adiabatic or isothermal process while accounting for viscous losses derived from flow-obstructions. A parameter sensitivity analysis revealed how the unvented contaminant mass varied with deviations from the nominal case and found that approximately 65%–95% of the initial mass of water is expected to vent out of the aeroshell. The results were compared to higher fidelity COMSOL Multiphysics simulations, which include effects of heterogeneity, diffusion, heat transfer, and reduced gravity to evaluate the implications of the reduced zero-dimensional formulation. The simulations predict that of all the sensitive surfaces external to the rotorcraft, water is expected to only reside on the photodiode and methane sensor optical surfaces at the conclusion of EDL.