where is the distance from the point of suspension to the center of mass of the model. To create the initial displacements and the required direction of relative velocity of the center of mass of the model of the active spacecraft, a marking of the areas under the models is used. Testing is usually done only in normal conditions. To create displacements in the sixth degree of freedom of each model Un the vertical direction) the suspension may be supplemented by a tracking drive which is adjusted to a force equal to the weight of the model In the testing the basic parameters of the process are recorded (linear displacements of the models, their angular velocities, overloads, displacement of shock absorbers, etc.) and motion pictures and photographs are taken. Tn the development of a docking device for the Gemini-Agena project, as well as in the first stage of work on the Apollo project, NASA and associated firms created several complex mechanical test units, which were used to test scale models and the real constructions [45]. These units used suspensions on cables and supports on air cushions; the models of the spacecraft were attached by Cardan joints placed at the centers of mass of the models; they also used tracking drives. The test unit created to test the Gemini docking device contained size and mass models of the craft and the Agena rocket suspended on cables 17.2 m long. Analogous test units were created in the initial stage of development of the docking device for the Apollo spacecraft, with suspension on air cushions and sliding on ice. A comparative analysis was made of several test units to test docking, and the schematic of the complex mechanical test unit was described [42] (Figure 7.5). To shift the models it was proposed that a suspension be used with support on an air cushion and a tracking drive for vertical displacements. The models were equipped with acting control systems. This schematic was not implemented, but clearly demonstrated the complexity and great size of full-scale complex mechanical test units, and the lack of universality. In the following stages great attention was devoted to hybrid complex test units.
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