Abstarct: High-altitude research, concering the characteristics of free molecular flow in aerospace, has become more prominent in recent years, from the return of the biocapsule to the placement of the satellite in orbit. Rarefied gas, due to the conditions of fluid discontinuity and its non-equilibrium in the atmosphere, it is not possible to use conventional methods of computational fluid dynamics because of assumption of continuity prevails over computational fluid dynamics (CFD) equations. For this reason, the computational method of discontinuous fluid in rarefied gas flow has been developed similar to the DSMC method. In this dissertation, the aim is to calculate the drag force on the satellite. Initially, the ultrasonic flow on a flat plate in the free molecular flow regime is investigated by direct Monte Carlo simulation using Fortran numerical code and OpenFoam software. In this regard, using the developed two-dimensional numerical code DMSC, a flat plate and aerodynamic force calculations are studied and simulated. The developed numerical code with an error of about 10% is shown to be a reliable tool for calculations related to dilute gas regime in high Nudson numbers. Due to the difficulty of entering any type of geometry in the numeric code, OpenFoam software has been used and the results of a flat page have been reviewed and re-validated. It has been shown that the software is capable of predicting dilute gas flow at a speed of 1412.5 m / s at a density of 3e19 kg / m3 with an error of less than 15%. In order to develop the results, the vertical plane in front of the current has been simulated by the software and the aerodynamic forces on such a plane have been calculated in the presence of a satellite in Leo orbit. It has been shown that in the conditions of very rarefied gas at an altitude of 150 km, the density is 2.074e-9 kg / m3 and the flow velocity is 2500 m / s. Then, in order to innovate in the results, the aerodynamic coefficients entered on the screen at different angles are investigated. The developed software can be implemented for any type of geometry to calculate the drag force on the satellite and can be used for research in this field.