The paper presents the results of research to determine the dynamic component of the force of the jet stream of a microwave ion engine. The dynamic component was determined by an adiabatic calorimeter based on a heat flux density sensor. Experimental studies have shown that with a working fluid consumption (nitrogen) from 0.01 to 0.08 mg/s, the thrust of the micro-motor was from 1.45 to 13 μN. The calorimetric method gives inflated thrust values presumably due to ohmic heating in a DC glow discharge.