The guidance contained in this document can be categorized as "design features" or "program features". The design features are those which bear directly on the technical aspects of a concept. Program features relate to the management focus that brings about the implementation of the concept.
- Design Features: These are measurable criteria. A number may be assigned to these for current systems. For future systems a target may be set which is then the "design target". The more improvement is made in each criteria the greater the correlation to meeting more vague, qualitative goals such as affordability of operation or high flight rate. These capture the recurring aspects of reusable space transportation systems.
- Program Features: These are measurable criteria. In general these present more of a challenge to baseline or set new targets for. These capture the non-recurring aspects of a reusable space transportation system.
Major characteristics of the guidelines are:
Prioritized:
The first 29 of the design features and the first 9 program features correlate very strongly to effectiveness and efficiency respectively. Effectiveness refers to results such as being low cost to buy and operate. Efficiency refers to how much was spent in time or money to get to that final product. The higher the rank (1, 2, 3, …) the more strongly the features correlate to qualitative "wants" such as low life cycle cost which includes low cost to develop, manufacture, buy and operate.
Numeric:
Numbers exist for where we are in many areas. Hence numbers may be assigned for how much we wish to improve.
Directional:
A sense of direction can result from assessing a future concept against these features. Relative merit can be assessed among multiple concepts. Assessing a set of design variables against these features will not result in quantitative life cycle cost estimates, schedule timelines or dollars per pound to orbit. The intent here is to assist in determining strategic directions for improvement which may then be more quantitatively assessed by implementing more detailed analysis, methods or models. This communication of practical engineering information can aid in focusing more formal requirements (Blair and Ryan 1992)6.
More detailed subsystem understanding and iteration on the implemented results of QFD’s, based on lessons learned, technology demonstration and product experience, are required to fully exploit the QFD method. In this way quality, meeting customer demands and growing markets, is built into the technology across many levels. From this approach, detailed relationships between features and costs in space transportation systems can eventually mature.
Return to KSC Next Gen Site
Edgar Zapata, NASA Kennedy Space Center
Shuttle Process Engineering Directorate, Fluid Systems Division