Postflight Thermal Protection System Analysis of Hayabusa Reentry Capsule

The thermal response of the ablative thermal protection system of the Hayabusa capsule is calculated along the most probable reentry trajectory by using the integrated analysis method. The analysis method consists of an axisymmetric nonequilibrium Navier-Stokes flow solver and a radiative heat transfer analysis code loosely coupled to an ablation thermal response code. The calculated results are compared with the flight data obtained at the present time. It is found that a reasonable agreement is obtained between the calculated surface temperature and the temperature values estimated from the DC-8 airborne observation and the ground observation. In contrast, the calculated surface recession overestimates the measurement along the wall surface by a factor of three. It is also found that the density distributions inside the ablator can be reproduced reasonably both at the stagnation point and at the downstream region by taking account of the conventional surface reaction set and nitridation reaction with a laminar boundary condition. Especially for the thickness of the char layer at the downstream region, calculation overestimates the flight data when the effect of turbulence due to the pyrolysis gas is considered, whereas it underestimates the flight data when the effect of surface roughness of the ablative thermal protection system is taken into account.