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Spacefaring America is about how America can start on the path towards becoming a true spacefaring nation by building integrated spacefaring logistics infrastructure capabilities to provide Americans with the ability to routinely and safely access and operate in space–to enable Americans to be spacefarers.
While many believe that building such infrastructure capabilities is decades in the future because of some technological space access barrier (see Spacefaring America blog 5), in fact U.S. aerospace industry now possesses the technological capability to start to develop and deploy near-term space logistics systems. This blog explains what “near-term” means as I use it.
What is a near-term system design? A near-term system design is one that can enter full-scale systems engineering and manufacturing development without first requiring significant additional enabling technology maturation research in the laboratory. What this means is that all critical technologies are either in operation or have been successfully brought to a stage of maturity (technology readiness) where their incorporation into the system design is believed to be possible without unacceptable costs, risks, or schedule delays.
How can the technology readiness be established? In the 1990s, NASA addressed this question and developed a Technology Readiness Level (TRL) scale to provide improved consistency in assessing a technology’s maturity. The figure below illustrates the TRL scale.
On this scale, a new scientific principle observed or reported is given a Level 1 rating while the application of this principle in an operational system is given a Level 9 rating. This scale can be used to filter new technologies to see which could be considered for inclusion in a new design.
What circumstances establish what TRL to use? This depends on when the new system is desired to be placed into operation and what level of risk is acceptable.
For example, if a conceptual design analysis is being undertaken for a new system to enter into operation in 20 years, then technologies with a TRL perhaps as low as 3 could be considered to better understand what advantages these new technologies may yield in terms of system performance and cost. (In fact, such early conceptual design analyses are routinely undertaken to help laboratory planners better understand which investments in new technologies have the biggest “bang for the buck.”) A 20-year development timeline is sufficient for up to 12 years of further technology maturation to be undertaken before the final system design is established at the end of preliminary design.
If a conceptual design analysis is being undertaken for a system that is desired to be operational in the near-future (6-8 years), then, obviously, only more mature technologies can be used. In this case, a TRL cut-off of 6 may be imposed. Only those technologies where, at a minimum, a system/subsystem model or prototype has been successfully demonstrated in a relevant environment would be considered.
This point is generally reached at the conclusion of the preliminary design when the final system design is established and detailed engineering design and production planning are started.
If an urgent need arises for a fix to an important problem, such as a military threat, then additional development risk may be acceptable. In this case, parallel technology development and system design and production planning are undertaken. The development of the atom bomb and, in particular, uranium enrichment during World War II are good examples of this approach. This approach usually requires multiple paths or technology solutions to be undertaken simultaneously in the hope that at least one will work adequately and be able to be fielded.
Who selects the technologies? The appropriate person to select the technologies is the one whose responsibility it is to deliver a successful product. For an operational system, the selection of the technologies is made by the Chief Systems Engineer either directly through design approval or by recommendation to the Program Manager. For an experimental system, such as the National Aerospace Plane/X-30, the selection of the technologies is made by the Chief Scientist and Chief Systems Engineer jointly or they jointly provide recommendations to the Program Manager. It is important to understand that an operational system and an experimental system have different success criteria. A successful operational system delivers a safe and affordable operational capability. A successful experimental system provides a means of testing the maturing technology in an operationally relevant environment.
How are criteria used to transition technology? Achieving a useful TRL 6 technology status is not simple. The decision that a potentially useful technology has achieved this level of maturity lies with the Chief Systems Engineer. He/she has to be convinced that the technology has, in fact, been successfully demonstrated to work in an environment relevant to the system being developed and meets other important performance and operability constraints such as weight, volume, and power required. To aid this transition, quite often a written series of qualitative and quantitative transition criteria are established that define what “successfully demonstrated” means to the Chief Systems Engineer. These criteria then provides a check list around which the technology demonstration program can be organized and executed.
The obvious limitation on the use of technology transition criteria is that a “near-term” system development, that is moving quickly through the conceptual design steps towards completing the preliminary design, may not be able to tap into ongoing technology development efforts and wait for new technologies to become sufficiently mature. In this case, the Chief Systems Engineer will exercise engineering judgment, based on vendor information and successful similar uses of the technology, to select which technologies that are less than TRL 9 to include in the planned design.
What types of aerospace systems are generally near-term? Most new commercial aircraft programs are near-term system solutions using TRL 6-9 technologies. In contrast, most U.S. military aircraft systems start with technologies that are less mature. Hence, such systems generally cost more to develop and require substantially more time than commercial aircraft programs. More advanced technologies are generally needed in the military system to effectively counter new and anticipated threats, to increase performance, or to incorporate new mission capabilities. Once these advanced technologies are identified, the initial phase of the total system development focuses on technology maturation and risk reduction to bring the initially TRL 3/4/5 technologies to TRL 6/7 when the detailed design of the system is initiated. Similar circumstances exist for military satellite development programs compared with commercial satellite programs. It is, however, important to note that many (perhaps, most) technologies in commercial systems were originated and matured in previous military programs.
Why is understanding the technology readiness levels for proposed new programs important? In a competitive environment where “selling” the program is the first measure of success, some basis for comparing technology maturity and program risk against the “anticipated” operational capability must be used. The TRL scale provides one basis for such comparisons.