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Description
An aerothermodynamic analysis of representative aerocapture and entry flows in Neptune is discussed in this work. Direct entry and aerocapture trajectories are taken from the literature, and peak heating points (18 km/s at 80km altitude for a direct entry, 29km/s at 130km altitude for an aerocapture trajectory) are accordingly selected. Two standard 60º and 45º sphere-cone shapes are considered, and flowfield solutions are computed for the forebody region, accounting for post-shock chemistry and thermal nonequilibrium effects, and yielding surface heat fluxes from convective heating. These results are complemented with a radiative transfer calculation using a line-by-line approach coupled with a ray-tracing routine, yielding surface heat fluxes from radiative heating.% Two reference atmospheric compositions are considered. The first one is nominally composed of 80\% \ce{H2} and 20\% \ce{He}, similar to the other gas giants such as Jupiter and Saturn, and the second one accounts for a small percentage of \ce{CH4} (about 1.5\%) that is known to be present in Uranus and Neptune.
There a strong impact of the small \ce{CH4} percentage on the predicted radiative wall heat fluxes, which increase significantly as a result of the presence of high-temperature carbonaceous species in the shock-layer. Particularly for the entry point where the entry velocity is lower, the accounting for the small \ce{CH4} portion of the gas changes the wall heat fluxes by several orders of magnitude, from 0\% to about 50\% of the total heat fluxes.% along the capsule surface.
It is also found that the flow features behind the shock differ significantly depending on the capsule shape. The post-shock sonic line is near the sphere-cone transition zone for the 45º sphere-cone shape and starts detaching from the boundary layer for angles above 55º, up to the point where the flow becomes entirely subsonic up to the spacecraft shoulder at 60º. It is concluded that more streamlined shapes will be more aerodynamically stable.
Summary
An aerothermodynamic analysis of representative aerocapture and entry flows in Neptune is discussed in this work. Direct entry and aerocapture trajectories are taken from the literature, and peak heating points (18 km/s at 80km altitude for a direct entry, 29km/s at 130km altitude for an aerocapture trajectory) are accordingly selected. Two standard 60º and 45º sphere-cone shapes are considered, and flowfield solutions are computed for the forebody region, accounting for post-shock chemistry and thermal nonequilibrium effects, and yielding surface heat fluxes from convective heating. These results are complemented with a radiative transfer calculation using a line-by-line approach coupled with a ray-tracing routine, yielding surface heat fluxes from radiative heating.% Two reference atmospheric compositions are considered. The first one is nominally composed of 80\% \ce{H2} and 20\% \ce{He}, similar to the other gas giants such as Jupiter and Saturn, and the second one accounts for a small percentage of \ce{CH4} (about 1.5\%) that is known to be present in Uranus and Neptune.
There a strong impact of the small \ce{CH4} percentage on the predicted radiative wall heat fluxes, which increase significantly as a result of the presence of high-temperature carbonaceous species in the shock-layer. Particularly for the entry point where the entry velocity is lower, the accounting for the small \ce{CH4} portion of the gas changes the wall heat fluxes by several orders of magnitude, from 0\% to about 50\% of the total heat fluxes.% along the capsule surface.
It is also found that the flow features behind the shock differ significantly depending on the capsule shape. The post-shock sonic line is near the sphere-cone transition zone for the 45º sphere-cone shape and starts detaching from the boundary layer for angles above 55º, up to the point where the flow becomes entirely subsonic up to the spacecraft shoulder at 60º. It is concluded that more streamlined shapes will be more aerodynamically stable.
