This paper presents the experience of software architectural design process for the microsatellite board computer based on formal language SysML. The design is achieved by top down method, which aims to set events and processes for satellite systems work by drawing SysML diagrams. In the design environment thanks to diagrams is generated program structure, which provides reliability and high-speed operation. Acquired experience shown that due to the reverse design (reverse engineering) may be reduced time testing and the design environment will allow correction and automatic generation of electronic documentation.