drawbacks of hybrid test units are the complexity of the testing complex as a whole, and the introduction of additional distortions in the reproduced process due to the operation of highly dynamic powerful drives. Complex test units can, in principle, reproduce the final part of the approach and mooring, including the participation of a pilot [35]. However, analysis has shown that the combination of these two parts of the connection of spacecraft in one test unit is inexpedient since the complexity of the equipment used increases substantially, as does the size of the test unit. At the same time the basic goals in the implementation of the initial stages of docking, which are the final parameters of approach, are very different in the modeling of these two sections. To reproduce the approach the control system minimizes the relative displacements and maintains nominal velocity; thus deviations and errors here are usually small, and testing serves to determine the possible scatter of initial conditions. Hsing the resultant data on the final parameters of the approach (see section 1.3) the critical combinations of initial conditions are determined which include maximum linear and angular displacements and extreme values of velocities. Tn modeling of the docking these parameters should be accurately reproduced. These concepts are the basic reasons why approach and docking are tested in different test units. Docking is reproduced, as a rule, without the participation of a pilot. For a deeper understanding of the essence of the processes which occur in docking, especially in the presence of manual control, it is expedient to include pilots in the operation of the test units. 7.7.1. Complex Mechanical Test Units To test a number of docking devices, including the APDA, a complex dynamic test unit was used which consisted of two spacecraft models which were suspended on cables through three-stage hinges placed at the centers of mass of the models. The suspension provided five degrees of freedom of displacement of each model. The horizontal components of the force of gravity sin , where is the mass of the models , g is free fall acceleration, and a is the angle of deviation of the cable from vertical, which is compensated by a spring mechanism (Figure 7.4). The models have the same masses and moments of inertia as the
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