passive state of the APDA the catches of the latches are released on the hull. Three lever mechanisms are used, driven by rotating type electromagnets. Linkage is signaled by three contact sensors located on the face of the ring. A detailed comparison of the APDA docking mechanisms created using the same technical requirements and carrying out the same functions of docking and undocking of the same spacecraft with the same initial conditions, and analysis of various schematics of peripheral docking devices is given in Chapter 2 (see section 2.4.3). One must note the following: the Soyuz APDA is a purely electromechanical construction without hydraulic or pneumatic elements, which (in the opinion of American specialists) is an advantage. After the creation of an electro-hydraulic APDA, NASA signed a contract with one of the firms to develop an electromechanical variant which was examined even in the initial stage of the work. Although the Soyuz APDA has a significantly smaller mass (269 kg) than the Apollo APDA (420 kg without the tunnel hatch), apparently both designs are equivalent. Mechanisms of the docking frame. In planning based on the schematics of the locks of both APDAs the system of locks of the docking device of the Soyuz- Salyut complex was chosen. The locks of the docking frame on the Apollo (Figure 1.30) were made with the following basic differences: The main drive of the system which retracts and opens the active clamps was installed directly in one of the locks. Back-up opening is done by an additional drive with an independent closed cable connection, simultaneously activating the mechanism to open the active and passive lever type clamps (Figure 1.31). The main and additional electrical drives of the locks were identical and constructed from the same basic elements as the docking mechanism drive (the alternating current electrical engines, the gear-type differential, the terminal switches on the microswitches, etc.). The installation of the drive on the lock was more reasonable in configuration, and the heavy-duty schematic was also used in the development of
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