The kinematic scheme and construction of the combined docking device with differential connections are relatively complex and contain a significant number of moving elements. Moreover, as in all electromechanical docking mechanisms, the shock absorbers have an increased inertia. 2.9. Redundancy in the Principal Schemes The use of the method presented in section 2.3 is based on an analysis of potential failures, and makes it possible to validly use redundancy in the principal construction schemes and in the control schemes of the developed docking devices. The use of redundant elements is a complex problem which requires detailed analysis of the properties of each specific principal scheme. At the same time it is possible to develop general recommendations. Relow we describe general approaches and partial solutions developed in practice and obtained using analysis of created and developed docking devices. 1. Unforeseen opening of the joint is a criticality category T failure and may be caused by the disintegration of a number of elements, the actuation of mechanisms or random commands (see section 3.3.3). To exclude spontaneous opening of the joint one must eliminate all possible causes. This is attained by a number of design and construction considerations. First of all, the most reasonable is a construction consisting of several independent sets of locks. The back-up undocking of these sets, including their control, should be structurally and functionally separated. Sets or subsets may be placed on one active docking assembly or on both docking assemblies, as was done in the Soyuz-Salyut docking device. To exclude the issuing of false or spontaneous commands, the control schemes of the lock drives and the back-up pyrotechnics must have redundancy in the shielding from unforeseen firing, which usually is done in the form of blockage of the issuing of the undocking commands; shut-off of the electrical power to the circuit controlling the lock drives during flight in the docked state is also provided f or. During docking of androgynous docking devices the set of locks on the passive assembly are back-up locks, and may be used to exclude opening of the oc
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