Determination of Forces and Moments at the Base of a Spacecraft Undergoing Sine Vibration Testing

When a spacecraft undergoes sine vibration testing, forces and moments acting at its base are important information sought, more importantly, at the fundamental modes of vibration. The moment acting is presently determined using the finite element-based mathematical model of the spacecraft. The force acting is often determined/verified through the electric current in the armature of the shaker or through employing a force measurement device. In this work, a simple methodology to experimentally determine the moments at the base of a spacecraft, which is based on the strains measured at suitable locations, is presented. The required moment-strain relation is established by subjecting the spacecraft to low frequencies of excitation and measuring the corresponding strains. It is shown that the same methodology can be adopted for measuring forces acting at the base, too. To validate the results obtained through this technique, they are compared with those obtained using a finite element-based mathematical model, and they compare very well. This simple methodology can be used to accurately determine the moments and the forces without needing a finite element-based mathematical model. The mathematical model is used in this work only to validate the results obtained through the proposed method, and no such model is required while applying this methodology to another spacecraft.