SMAD

18 The Space Mission Analysis and Design Process
possible, it would be desirable. to create a chart similar to Fig. 1-5 based on even crude
estimates of spacecraft cost Doing so provides a much stronger basis for, establishing
mission requirements and, e.g., determining whether we should push harder for a
longer spacecraft lifetime or back off on this requirement to reduce spacecraft
cost
Having made a preliminary estimate of mission requirements and constraints, we
proceed in Chap. 2 to define and characterize one or more baseline mission concepts.
The issue of refining requirements and assessing how well objectives can be met is
discussed in Chaps. 3 and 4.
References
Boden, Daryl G. and WIley 1. Larson. 1996. Cost Effective Space Mission Operations.
New York: McGraw-Hill.
Davidoff, Martin. 1998. The Radio Amateur's Satellite Handbook. Newington, CI':
American Radio Relay League.
Defense Systems Management College. 1990. System Engineering Management
Guide. Ft Belvoir, VA: U.S. Government Printing Office.
Kay, WD. 1995. Can Democracies Fly in Space? The Challenge of Revitalizing the
U.S. Space Program. Westport, CI': Praeger Publishing.
National Research Council. 1990. Strategy for the Detection and Study of Other
Planetary Systems. Washington, DC: National Academy Press.
Przemieniecki, J.S. 1993. Acquisition of Defense Systems. Washington, DC: American
Institute of Aeronautics and Astronautics, Inc.
Rechtin, Eberhardt 1991. Systems Architecting. Englewood Cliffs, NJ: Prentice Hall.
Ruskin, Arnold M. and W. Eugene Estes. 1995. What Every Engineer Should Know
About Project Management (2nd Edition). New York: Marcel Dekker,lnc.
Shisbko, Robert 1995. NASA Systems Engineering Handbook. NASA.
Wertz, James R. and WIley J. Larson. 1996. Reducing Space Mission Cost. Torrance,
CA: Microcosm Press and Dordrecht, The Netherlands: Kluwer Academic
Publishers.
Chapter 2
Mission Characterization
James R. Wert7, Microcosm, Inc.
Richard P. Reinert, BaD Aerospace Systems
2.1 Step 3: Identifying Alternative Mission Concepts
Data Delivery; Tasking, Scheduling, and Control;
Mission Timeline
2.2 Step 4: Identifying Alternative Mission Architectures
2.3 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 intelligtble 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 geosynchrono1JS
satellites. Eckart [1996] 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
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