DSMC Aero-Thermo-Dynamic Analysis of a Deployable Capsule for Mars Entry

A deployable capsule is made of flexible, high temperature resistant fabric, folded at launch and deployed in space at the beginning of the re-entry. This kind of capsule thanks to lightness and to low costs can be an alternative to the current “conventional“ capsules. The present authors already analyzed the trajectory and the aerodynamic behavior of such a kind of capsule during the Earth re-entry. In that study an aerodynamic longitudinal stability analysis and an evaluation of the thermal and mechanical loads for a possible, suborbital re-entry demonstrator, was carried out in both continuum and rarefied regimes. The results verified that a stable equilibrium condition is verified around the zero angle of attack and an unstable equilibrium condition is verified around the 180 angle of attack; therefore the capsule turned out to be self-stabilizing. In the present paper the trajectory, the longitudinal stability, the thermal and mechanical loads of the same capsule has been evaluated for a possible use in Mars entry. The present study is aimed at providing preliminary information considering both the diversity of the two atmospheres and the diversity of the two types of entry: ballistic, sub-orbital for Earth, direct for Mars and therefore of the initial entry velocity. The parameters were compared with those along the Earth re-entry. As the computer tests have been carried out at high altitudes, therefore in rarefied flow fields, the use of Direct Simulation Monte Carlo codes has been mandatory. The computations involved both global aerodynamic quantities (drag and longitudinal moment coefficients) and local aerodynamic quantities (heat flux, pressure and skin friction distributions along the capsule surface). The results verified that the capsule at high altitude (100 km) in Mars entry is not self-stabilizing; it is stable both around the nominal attitude or at zero angle of attack and around the reverse attitude or at 180 deg angle of attack. Furthermore, due to the much higher entry velocity, the local quantities are of several orders of magnitude higher than the ones in Earth re-entry.