F

Number of Satellites

Fig. 3-5. Hypothetical Coverage Data for FlreSat See text for definitions and discussion. As discussed in Sec. 7.5, satellite growth comes in increments or plateaus. These are assumed to be 2-satellite increments for RreSat

Number of Satellites

Fig. 3-5. Hypothetical Coverage Data for FlreSat See text for definitions and discussion. As discussed in Sec. 7.5, satellite growth comes in increments or plateaus. These are assumed to be 2-satellite increments for RreSat

If we assume an initial goal for time late of no more than 5 hours, we see from the plot that a system of 6 satellites can meet this goal. Alternatively, a 4-satellite system can achieve a time late of 6 hours. Is the smaller time late worth the increased number of satellites and the money to build them? Only the ultimate users of the system can judge. The additional warning may be critical to fire containment and, therefore, a key to mission success. However, it is also possible that the original goal was somewhat arbitrary, and a time of approximately 5 hours is what is really needed. In this case, fire-fighting resources could probably be used better by flying a 4-satellite system with 6 hours time late and applying the savings to other purposes. Again, mission utility analysis simply provides quantitative data for intelligent decision making.

Of course, we must remember that the number of FireSat satellites will depend not only on the utility analysis but also on politics, schedules, and resources. The public must see FireSat as an appropriate response to the problem, as well as an efficient use of scarce economic resources compared to, for example, more fire fighters. In addition, a satellite system may serve several missions, with multiple mission criteria and needs. Just as we cannot apply only one criterion to some system drivers, we may not be able to balance numerically the several criteria for mission selection. Instead, the developers, operators, and users must balance them using the insight gained from the system trades and mission utility analysis.

Having undertaken a round of system trades, evaluated the mission utility, and selected one or more baseline approaches, we are ready to return to the issue of system requirements and their flow-down to various components. Chapter 4 treats this area, which is simply the next step in the iterative process of exploring concepts and defining requirements.

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