Currently, the number of launches of small spacecraft weighing up to 10 kg is noticeably increasing in the world. One of the main reasons for this growth is the relatively short development time of the satellite, the cost of its manufacture and launch. The range of tasks performed by such devices is steadily growing. In this regard, devices for the movement of the center of mass and around it become clamorous. They will compensate for disturbing effects, as well as accurately orient and stabilize the spacecraft. The maneuvering unit can serve as such a device. The propulsion system is one of its main elements. The choice of a particular propulsion system is clamorous at the design stage. It should take into account the specific requirements for the installations of such devices. Due to the limitations inherent in such satellite, mass estimation is an urgent task. In this paper, the main subsystems of the maneuvering unit, their elements and the functions performed by them are considered. Propulsion systems based on various physical principles are presented, their structural schemes are shown, as well as the main parameters. A method of preliminary calculation of the mass of the maneuvering unit based on the mass of the spacecraft, the required reserve of relative velocity and engine parameters is proposed and tested.