Dynamic Response of a System Driven by Thermal Actuation

During its operational life a spacecraft undergoes continuous variations of its thermal field. The design of the thermal subsystem takes into account all of these conditions and ensures the temperature does not exceed the limits consistent with the correct operation of the apparatuses and the nominal sequence of the events. What is usually left out of the analysis is the impact of the thermal field variation on the dynamic response of the structure and of its interaction with the control system. The thermally induced prestress can in fact shift the frequencies of vibration and strongly modify the nature of the constraints. These two major aspects, if not taken properly into account, can reduce or even frustrate the control system performance which is largely based on a priori knowledge of frequencies and modes. In order to highlight the basic concept, very simple systems have been analysed and discussed.