When developing modern and promising aerospace technology models, the relevance of simulation of the flow around apparatuses (spacecraft) of various geometric shapes in a transitional mode corresponding to the flight in the region of the upper layers of the atmosphere and near space is growing. Solving the Boltzmann equation, which most adequately describes this process in the framework of kinetic theory, still remains a difficult task. To solve this equation, the Monte Carlo statistical methods are used quite successfully. An example of such a method is the direct statistical simulation, or, less common but also well-established in rarefied gas dynamics, the test particles method (TPM). The aim of this work is to study the effect of geometric proportions of simply-shaped orbiting objects during uncontrolled descent to dense layers of the atmosphere on their drag coefficients. Such objects may be elements of space debris or spacecraft of appropriate shapes and proportions. The studies were based on the results obtained by numerical simulation of TPMs on uniform rectangular grids. The shape of the orbital objects was set in the form of a circular cone, cylinder, rectangular parallelepiped of various elongations, and spheres. The calculations were carried out in a wide range of attack angles. The characteristic dimensions of the body class in question varied from 2 to 12 meters. According to the standard atmosphere for such characteristic dimensions, the transitional flow regime is realized at altitudes from 90 km to 180 km. It was found that the calculated values of the drag coefficients in the transition regime are in satisfactory agreement with the experimental data and calculations on the theory of local interaction, and at an altitude of 300 km, they correspond to the control free molecular values obtained by analytical formulas. The dependence of the drag coefficients of the bodies of the considered shapes on the angle of attack and flight altitude was studied. The influence of the choice of the characteristic area on the range of values of the calculation results is shown. The drag coefficient of the considered class of bodies at the entrance to the dense layers of the atmosphere using the TPM was calculated for the first time. Satisfactory agreement of the obtained results with the available experimental and calculated data confirms the effectiveness of the applied method in transition mode. This makes it possible to use it in practical calculations of the parameters of the external environment effect on the spacecraft in the most difficult to study altitude ranges corresponding to the transitional flow regime.
