Estimates of Equilibrium Temperature on the Surface of the Spherical Blunt of the Descent Orbiter

The descent of a stabilized capsule from a low near-earth orbit along a ballistic trajectory is considered. The descent of a stabilized capsule from a low Earth orbit along a ballistic trajectory is considered. A reliable preliminary estimate of the intensity of the thermal impact of the air flow, which enters the surface of the capsule, is the equilibrium temperature of this surface. The value of the equilibrium temperature follows from the condition of equality of the density of the total heat flux brought to the surface and the density of the heat flux, removed due to the own radiation of this surface. Based on the peculiarities of the heat exchange process on the surface of the spherical blunt capsule three sections of the trajectory are distinguished. At free-molecular flowing of the blunt, at the section of descent the intensity of heat exchange is assumed to be proportional to the energy of the molecule flow. At the section corresponding to the continuum flow regime, the intensity of convective and radiative heat transfer is estimated by empirical dependences obtained by processing the calculated and experimental results. When combining laminar and turbulent flow modes on the attenuation surface, the highest of two local values of convective heat flux density is taken. At the intermediate section of the descent, the Knudsen number is taken as an argument determining the intensity of convective heat transfer, and empirical dependences are used to estimate the radiation component. A quantitative analysis of the change in the time of descent of the maximum value of the equilibrium temperature on the blunted surface for a ball capsule and a capsule with a ball segment was carried out. The results of such analysis are the purpose of the present work and allow to identify the most heat-stressed areas of the descent trajectory on the blunt surface at the preliminary stage of the design and to choose the acceptable materials of the thermal protection coating