platform tracks this calculated position. The process is done continuously in a closed circuit with reproduction of the force interactions, the motion between them, linkage, damping of relative oscillations, equalization, and partial coupling. As practice has shown, the formation of a rigid connection of docking frames causes significant difficulties due to the generation of high-frequency auto-oscillations in the closed circuit. To relieve the platform of the weight of the moving parts of the docking mechanism, primarily the ring with guides of the APDA, there is a mechanism with cable connections and elastic elements. The weight of the docking assembly on the immobile platform, which acts on the force sensors, is compensated in the measurement system. The test unit makes it possible to test with heating (to of the docking assembly using a system of thermal regulation in the chamber formed by the upper part of the force base, the moving platform, and the flexible casing. This type of hybrid test stand was first created in the US in work to test an experimental docking device [39]; the test unit made it possible to bring the model of the active spacecraft to a distance of 21 m with the use of guidance equipment and manual control. In the Johnson Space Flight Center (NASA) a hybrid complex test unit was created to test docking for the Apollo program [36]. The kinematics of the test unit were such that the tracking hydraulic drives shift the platform with the docking assembly installed on it with four degrees of freedom (transverse displacements with rotation in yaw and pitch). The other platform with the second docking assembly can shift with two degrees of freedom (in the longitudinal direction and in roll). This kinematic scheme of the test unit was very complex, and it was difficult to provide the required rigidity of the platform. Thus, in work on the APDA the test unit was reworked according to the scheme described above, with one moving platform installed on six drives. Due to the complicated conversions of coordinates done by the computer, the kinematics of the test unit were greatly simplified, and this improved its dynamic characteristics. The hybrid test unit and all of its systems are a complex (in construction and in use) and expensive technical complex with a great number of precision
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