Aerothermodynamic analysis of Neptune ballistic entry and aerocapture flows

An aerothermodynamic analysis of representative aerocapture (29 km/s) and entry (18 km/s) flows in Neptune is discussed. Two 60 degrees and 45 degrees sphere-cone shapes are considered, and chemically-reactive, nonequilibrium flowfield solutions are computed for the forebody region, yielding surface heat fluxes from convective heating. A radiative transfer calculation using a line-by-line approach coupled with a ray-tracing routine, yields surface heat fluxes from radiative heating. If the trace amounts of CH4 in Neptune's atmosphere are accounted for, they dramatically enchance radiative heating, as a result of strong radiative emission from carbonaceous species in the shock layer. For the 18 km/s entry point, radiative heat fluxes accordingly increase by several orders of magnitude, from 0% to about 50% of the total heat fluxes. The post-shock flow features further differ significantly depending on the capsule shape. The sonic line is near the sphere-cone tran-sition zone for the 45 degrees shape and starts detaching from the boundary layer for angles above 55 degrees. The post-shock flow becomes entirely subsonic up to the spacecraft shoulder at 60 degrees. More streamlined shapes will accordingly be more aerodynamically stable. (c) 2022 COSPAR. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/ by-nc-nd/4.0/).