About the Design and Programmatic Features, and the SPST
Customer demands for future space transportation systems include much greater affordability, responsiveness, dependability and dramatically lower life cycle costs including acquisition costs and research and development costs and risks. The purpose of this "Guide" is to provide a prioritized, high level set of design and programmatic features against which future space transportation systems may be evaluated to determine their degree of improvement over current systems and their ability to satisfy these customer demands. The guide may be used by a concept developer, a program manager, a technology developer or by designers at a total vehicle architecture level.
This guide was developed by the Space Propulsion Synergy Team (SPST) as part of its support to the Highly Reusable Space Transportation (HRST) project activities. The Space Propulsion Synergy Team (SPST) is a broad based group of diverse individuals from NASA, industry and academia, which has addressed in past and current efforts the direction of future space transportation systems and technology. The involvement of key backgrounds and areas of insight in the SPST has been an integral part of understanding and prioritizing areas for improvement.
During the past several years that the SPST, previously identified as the SPSG, has been active, they have developed and applied an effective process for comparative assessment of candidate space transportation systems and technologies. The process utilizes the strengths inherent in a team with diversified backgrounds and expertise; and the basic principles of a highly credible approach known as Quality Function Deployment (QFD). This approach assures that there is a direct link between the space transportation system capability and characteristics/attributes, and those required by the "customer".
Most important, this approach also includes the development and definition of "measurable criteria" to be utilized in assessing the degree to which a system concept or a technology enhances the system characteristics/attributes desired by the customer. These "measurable criteria" are presented in this guide and constitute the principle aid in the definition and design of an HRST or any advanced space transportation system.
However, it was realized that the system concept with the most attractive attributes and hence the greatest long term payoffs can lose support when programmatic constraints are tight. National space policies, international agreements, schedule, budget, availability and maturity of technology are a few of the examples of these "programmatic constraints". Therefore, the SPSG devised a dual assessment and prioritization system that balances these two driving forces. A graphic visualization of the process is shown below. This approach enables decision makers to make decisions based on knowledge of both the long term strategic payoffs, "desired attributes" and the individual projects "programmatic constraints". The later are subject to short term changes, but once the long term strategic payoffs, "desired attributes" are established, they remain quite stable.
The stability of the "desired attributes" or long term benefits, in a transportation system has been thoroughly demonstrated over the past several years by the SPST and other organizations/groups. The SPST (SPSG) has developed and prioritized the desired attributes in a space transportation system several times, each time with a different group of individuals with consistent results.
Also, these sessions were in support of several different advanced space transportation programs. They included a follow-on exercise for the Access to Space studies and support of the RLV project definition and technology plan. Both of these activities utilized the process previously developed and exercised by the SPSG. The definition and prioritization of the required system attributes that resulted from each of these exercises were very consistent with those previously developed and were also consistent with those recently formulated for the HRST.
There have been other activities using the same basic process, notably several initiated by the USAF, but including industry and NASA participation. These activities also resulted in the identification and prioritization of required/desired space transportation system "attributes" that were very similar to those presented in this guide.
This dual prioritization approach is addressed in further detail in the next section of this report as are the definitions of the programmatic constraints.
Although the focus of the information provided in this guide has been within the context of the Highly Reusable Space Transportation (HRST) project, the applicability is to any future reusable systems seeking to improve over a current system such as Shuttle.
The features or criteria around which this guide is organized must be considered as a whole. If a future space transportation system improves or not on any one particular feature is not as important in determining merit as whether it improves or not on the majority of the significant features. A full understanding of future systems in regards to this guide is considered crucial to understanding a sense of direction for improvement as well as an understanding of the relative merits of systems competing for further development, acquisition and eventually operation.
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Edgar Zapata, NASA Kennedy Space Center
Shuttle Process Engineering Directorate, Fluid Systems Division