There are many potential tradeoffs that can be

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Unformatted text preview: le flow of interface data exists between the upper and lower modules at functions F7 and F8. The lower module has complex interaction among its functions. The N2 chart can be taken down into successively lower levels to the hardware and software component functional levels. In addition to defining the data that must be supplied across the interface, the N2 chart can pinpoint areas where conflicts could arise. NASA Systems Engineering Handbook NASA Systems Engineering Handbook used to perform and record the analysis of time critical functions and functional sequences. Additional tools such as mathematical models and computer simulations may be necessary. Time line analysis is performed on those areas where time is critical to the mission success, safety, utilization of resources, minimization of down time, and/or increasing availability. Not all functional sequences require time line analysis, only those in which time is a critical factor. The following areas are often categorized as time critical: 1) functions affecting system reaction time, 2) mission turnaround time, 3) time countdown activities, and 4) functions requiring time line analysis to determine optimum equipment and/or personnel utilization. An example of a high level TLS for a space program is shown in Figure B-9. Time line analysis adds consideration of functional durations and is used to support the development of design requirements for operation, test and maintenance functions. The time line sheet (TLS) is For time critical function sequences, the time requirements are specified with associated tolerances. Time line analyses play an important role in the trade-off process between man and machine. The decisions between automatic and manual methods will be made and will determine what times are allocated to what subfunctions. In addition to defining subsystem/component time requirements, time line analysis can be used to develop trade studies in areas other than time consideration (e.g., should the spacecraft location be determined by the ground network or by onboard computation us...
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