The term “docking system” is used to refer to domestic equipment, the complex of on-board equipment for monitoring and control, and the executive mechanisms of the docking device, including elements of automation and communications with other spacecraft systems. To control the docking device mechanism, an instrument is used which is usually called the docking control block, which performs two basic functions: 1) commutation of the engines and electromagnets of the drives; 2) logical processing of the control signals (from the operation execution sensors and from other interacting systems of the spacecraft) and processing of the commands issued in the commutation part of the instrument and in other systems. Figure 1.2 shows the main on-board and Earth-based means of control and monitoring which are used in docking and undocking of the Soyuz space transport ship and the Salyut orbital station. The interconnection of systems to perform operations is done through a central control system by equipment which provides for: 1) transmission of commands from the command radio line and from the cosmonaut panel; 2) exchange of commands with other systems (for example, switching off the spacecraft orientation and movement system on first contact); 3) blocking of the issuing of commands transmitted from the cosmonaut's panel and on the command radio line or automatically processed by the system for certain states of the mechanisms and sensors; 4) temporary monitoring and control of individual operations and automatic cycles. Blocking is widely used in the docking system, as it is in other spacecraft systems, to eliminate undesirable and dangerous actions, incorrect sequences of commands, etc. For example, to avoid unexpected or accidental undocking, before the issuing of the main command for separation of the spacecraft one must issue a preliminary command. In the absence of the preliminary command the electrical circuit of the main command remains open. To automatically shut down electrical power supply in case of premature stoppage of the drives or incomplete execution of operations, temporary monitoring is used. A special instrument processes electrical signals in a specific time sequence which is used in the docking control block to query the state of the system. For example, if by a certain time the drive has not reached a given position, the electrical supply to the system is shut off, and the warning indicator lights up on
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