Optimised Magnetic Field Strengths for Venus Atmospheric Entry using Magnetohydrodynamic Aerobraking

This paper investigates the optimal use of magnetohydrodynamic (MHD) aerobraking in order to minimise vehicle stagnation point heating during a Venus atmospheric entry. The 11.5 km/s entry of Pioneer’s large Sounder probe was considered, as it provided historic data for a Venus entry that endured extreme atmospheric heating and may benefit from MHD aerobraking. A magnetic field strength that could be varied with respect to the descent altitude was implemented and optimised to minimise the instantaneous peak convective, radiative and total heat flux, as well as the total integrated heat load. The optimisation was completed using two independent global search algorithms; a basin-hopping algorithm, as well as a genetic algorithm for verification. Porter and Cambel’s analytical model for estimating the drag coefficient of an axisymmetric, spherical body with a concentrically generated magnetic field was used to simulate the trajectories. The instantaneous peak total heat flux and the total integrated heat load are the most important heating parameters considered during thermal protective system design. However, in this study we found that both parameters are minimised by notably different optimised field strength curves. Peak total heat flux was reduced by 41% compared to the non-MHD case using a field strength that varied in response to the magnitude of the convective and radiative heat flux contributions. This was because increasing the applied magnetic field strength decreased convective heat flux, while simultaneously increasing radiative heat flux, due to the MHD induced increase in shock standoff distance. In comparison, the total integrated heat load was reduced by 23% by applying a constant magnetic field strength across the entire descent. Considering heat shield design, the peak heat flux typically informs the heat shield’s material and density, whereas the integrated heat load informs the required thickness. Therefore, whether a constant or dynamic field strength should be used is likely to depend on the mission’s objectives and constraints, which will define which heating parameter is more critical.