Multipurpose method for measuring the inertia tensor of the spacecraft



Videnkin N. A.

NPO “Technomash”, 40, 3rd proezd Mar’inoi Roshchi, Moscow, 127018, Russia



Nowadays, the rocket and space industry is extremely needed for a reliable test equipment, which is characterized not only by high accuracy, but is also able to work in automatic mode. Test rigs with computer-controlled static inertial characteristics may serve as a proper example. The operating technology of these rigs is designed to minimize the number of manual and transport operations.

Besides the accurate determination of static inertial characteristics — mass and center-of-gravity coordinates, it is possible to significantly increase the quality of spacecraft work process by measuring the dynamical inertial properties. It is especially important for interplanetary spacecraft and deep space stations. Thus, it is necessary to complete the structure of the static balancing test rig by measuring the spacecraft main central moments of inertia and the direction of its main central axes of inertia (the main parameters of the central inertia ellipsoid).

The main purpose of this work is the development of the multipurpose method for measuring the inertia tensor parameters of the spacecraft in its bound coordinate system. The method being developed is based on the existing static balancing test rigs.

The objectives of the work are:

1) To make the choice of the basic method for measuring the spacecraft parameters of the central inertia ellipsoid based on analysis of techniques used in practice.

2) To optimize the process of measuring the parameters of inertia tensor for objects with different ratios of inertial characteristics within the permissible loads on the rig.

It is necessary to carry out a comparative analysis of the current equipment models to choose the optimal base scheme of combined test rig it. Nowadays the development of test rigs is elaborated in many countries. The general trend of modernization is to increase the level of accuracy of measurement and automation of the measurement process. Leading companies in this field are «Space Electronics» (USA), «APCO Technologies» (Switzerland), FSUE «NPO «Tekhnomash» (Russia) and FSUE «TsAGI» (Russia). Significant disadvantages of the various types of equipment are low accuracy, the use of complex engineering solutions (current balance, air bearings) and the lack of technical means to measure all the parameters of the central ellipsoid of inertia without relocation.

It is suggested to use the method of inverted physical pendulum with a stiff fixation as basic for measuring the moments of inertia. The method consists in calculation of the moment of inertia about the axis by the measured values of period of harmonic torsional oscillations made with an elastic system. The value of stiffness coefficient of this system is calibrated. The dissipative forces are acted on a system and causing damping of the oscillatory process during oscillations. These forces include friction forces in rolling bearings, the friction force in the spring material, the frictional force of the air. The friction force makes a significant contribution to the dynamics of oscillations, so there is a problem of its compensation. Supplement the measurement system by the control device capable to create a self-oscillation process can serve as a solution.

To ensure the metrological parameters specified by the technical requirements of the test rig it is necessary to maintain the oscillations on strictly defined amplitude for spacecraft with different inertial characteristics.


moment of inertia, inertia tensor, balancing, test rig, spacecraft


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