James R Wertz Microcosm Inc Richard P Reinert Ball Aerospace Systems

2.1 Step 3: Identifying Alternative Mission Concepts Data Delivery, Tasking, Scheduling, and Control; Mission Timeline

22 Step 4: Identifying Alternative Mission Architectures

23 Step 5: Identifying System Drivers

2.4 Step 6: Characterizing the Mission Architecture

Mission characterization is the initial process of selecting and defining a space mission. The goal is to select the best overall approach from the wide range available to execute a space mission. Typically we wish to choose the lowest cost or the most cost-effective approach, and provide a traceable rationale that is intelligible to decision makers.

The initial process of mission characterization is discussed for general missions by Griffin and French [1991] and Pisacane and Moore [1994]. Elbert [1987,1996] and Agrawal [1986] provide similar discussions for communications and geosynchronous satellites. Eckart [19%] and Woodcock [1986] discuss this process for manned missions and Wall and Ledbetter [1991] do so for remote sensing. Boden and Larson [1996] discuss initial characterization for mission operations and London [1994] provides a similar overview for launch vehicles, with a strong emphasis on reducing cost Davidoff [1998] and Wertz and Larson [1996] discuss specific mechanisms applicable to low-cost and reduced cost missions.

The unconstrained number of mission options is huge, considering all possible combinations of orbits, launch systems, spacecraft, and mission concepts. The goal of this chapter is to prune this large number to a manageable level, without discarding options that offer significant advantages. We will do so by applying the requirements and constraints from Chap. 1 to pare down the list of alternatives. As an example, for most commercial communications applications, we would traditionally restrict ourselves to a geosynchronous orbit and only a few launch systems. However, the large number of low-Earth orbit communications constellations suggests that other options should be considered.

With requirements and constraints defined and alternative mission concepts selected, we must define each concept to the level required for meaningful comparisons. As Fig. 2-1 shows, we need to do this independently for each of the alternative mission concepts identified as "A" and "B" in the figure. Chapter 3 describes in more detail how we then evaluate the concepts, compare them in terms of cost and performance, and select one or more baselines. At the same time, we must keep track of the

Flg. 2-1. Concept Exploration Flow. One key for successfully Implementing this flow Is to iterate. Successive iterations through the Dow win result in greater understanding, and can uncover critical requirements and system drivers.

element and system costs using the characteristics generated in the study and the techniques in Chap. 20. This procedure results in a rough order of magnitude {ROM) cost and an understanding of relative costs to support Anther trades and system evaluations.

In common use, "mission concept," "concept of operations," and "mission architecture" are frequently interchangeable and, at best, vaguely defined. Throughout this chapter, we wish to clearly distinguish between them. The mission concept, discussed in Sec. 2.1, is a broad statement of how the mission will woric in practice. This should not be confused with mission operations, which provides the details of how people will operate and control the mission. The mission architecture, introduced in Sec. 2.2, is the mission concept plus a definition of each of the major elements of the mission.

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