The SPST approach to functional or performance requirements is a simplified "gate". For purposes of developing the criteria contained in this guide, which is strategic in nature, and understanding the interrelationships and priorities, the specific details on the performance of particular concepts and technologies is not required. However, in determining the transportation system performance closure or compliance there must be a growth or technology margin included at this early stage. Further detailed steps in the technology evaluation process requires that performance aspects of potential technologies, or whole transportation systems built from these technologies, be one of the basic building blocks in the decision making process.
One such example applies to rocket based combined cycle (RBCC) type vehicles. The following is one possible approach to maintaining a necessary tracking of the ability of a concept to reach closure and satisfy functional requirements.
Possible spreadsheet, with entries listed at one second intervals along the flight trajectory:
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Edgar Zapata, NASA Kennedy Space Center
Shuttle Process Engineering Directorate, Fluid Systems Division