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For example, does the spacecraft antenna acquire the tracking and data relay satellite (TDRS) only when the payload data are to be transmitted, or does it track TDRS continually to allow for the reception of emergency commands or transmission of emergency data? The FFBD also incorporates alternate and contingency operations, which improve the probability of mission success. These diagrams are used both to develop requirements and to identify profitable trade studies.
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Each block in the second level diagram can be progressively developed into a series of functions, as shown in the third level diagram on Figure 2. Each block in the first level diagram can then be expanded to a series of functions, as shown in the second level diagram for "perform mission operations." Note that the diagram shows both input (transfer to operational orbit) and output (transfer to space transportation system orbit), thus initiating the interface identification and control process. For example, the entire flight mission of a spacecraft can be defined in a top level FFBD, as shown in Figure 2. FFBDs show the same tasks identified through functional decomposition and display them in their logical, sequential relationship. Development of functional flow block diagrams įigure 2: Development of functional flow block diagrams įFBDs can be developed in a series of levels. FFBDs became widely used in classical systems engineering to show the order of execution of system functions. In the 1960s it was exploited by NASA to visualize the time sequence of events in space systems and flight missions. The modern Functional Flow Block Diagram was developed by TRW Incorporated, a defense-related business, in the 1950s. In 1947, ASME adopted a symbol set as the ASME Standard for Operation and Flow Process Charts, derived from Gilbreth's original work. Graham, Director of Formcraft Engineering at Standard Register Industrial, adapted the flow process chart to information processing with his development of the multi-flow process chart to display multiple documents and their relationships. A 1944 graduate of Mogensen's class, Art Spinanger, took the tools back to Procter and Gamble where he developed their Deliberate Methods Change Program. Mogensen began training business people in the use of some of the tools of industrial engineering at his Work Simplification Conferences in Lake Placid, New York. In the early 1930s, an industrial engineer, Allan H. Gilbreth's tools quickly found their way into industrial engineering curricula. The first structured method for documenting process flow, the flow process chart, was introduced by Frank Gilbreth to members of American Society of Mechanical Engineers (ASME) in 1921 as the presentation “Process Charts-First Steps in Finding the One Best Way”.
FFBDs are one of the classic business process modeling methodologies, along with flow charts, data flow diagrams, control flow diagrams, Gantt charts, PERT diagrams, and IDEF. The FFBD notation was developed in the 1950s, and is widely used in classical systems engineering.
FFBDs may also express input and output data dependencies between functional blocks, as shown in figures below, but FFBDs primarily focus on sequencing. Here, "functional flow" pertains to the sequencing of operations, with "flow" arrows expressing dependence on the success of prior operations. The term "functional" in this context is different from its use in functional programming or in mathematics, where pairing "functional" with "flow" would be ambiguous. Ī functional flow block diagram ( FFBD) is a multi-tier, time-sequenced, step-by-step flow diagram of a system’s functional flow. Figure 1: Functional flow block diagram format.