Aerothermodynamic Analysis of Aerocapture and Ballistic Entry Flows in Neptune Atmosphere

Neptune is one of the Solar system’s planets that are still unexplored, and mankind needs to be prepared for these new engineering challenges. For now, a lot of similarities are assumed between the atmospheres of Neptune and Jupiter. Specifically, both planets’ main components are believed to be molecular hydrogen and helium (in an approximate proportion of 80%/20%). However, Neptune’s atmosphere is also believed to have a small methane’s (CH4) percentage (1.5%). This work aims to evaluate the exact Neptune chemical composition (including CH4) influence in the aerothermal environment of a capsule entering this atmosphere. Different capsule’s shapes are considered (60◦ and 45◦ sphere-cones), and two trajectory points for two different mission types are studied: a ballistic entry trajectory point (around 80km altitude at 18 km/s) an and aerocapture trajectory point (around 130km altitude at 29 km/s). For both capsules, different trajectory points and chemical compositions (with and without CH4) are considered for the performed aerothermodynamic analysis, including both the convective and the radiative wall heat fluxes through the capsule’s wall. The results show that, when the small methane’s percentage is considered, the radiative wall heat fluxes increase significantly, particularly for the entry trajectory point. Finally, a brief aerodynamic analysis is performed for the aerocapture trajectory point, evaluating the aerodynamic coefficients for capsules with trim tabs. The capsule with a cone angle θc = 45◦ seems to present better performance, whereas θc = 60◦ is prone to aerodynamic instabilities.