Technology readiness levels (TRLs) are a method for estimating the maturity of technologies during the acquisition phase of a program, developed at NASA
 during the 1970s. The use of TRLs enables consistent, uniform 
discussions of technical maturity across different types of technology.
 A technology's TRL is determined during a Technology Readiness 
Assessment (TRA) that examines program concepts, technology 
requirements, and demonstrated technology capabilities. TRLs are based 
on a scale from 1 to 9 with 9 being the most mature technology.  The US Department of Defense has used the scale for procurement since the early 2000s. By 2008 the scale was also in use at the European Space Agency (ESA), as evidenced by their handbook.
 
The European Commission advised EU-funded research and innovation projects to adopt the scale in 2010. TRLs were consequently used in 2014 in the EU Horizon 2020 program. In 2013, the TRL scale was further canonized by the ISO 16290:2013 standard. A comprehensive approach and discussion of TRLs has been published by the European Association of Research and Technology Organisations (EARTO). Extensive criticism of the adoption of TRL scale by the European Union was published in The Innovation Journal, stating that the "concreteness and sophistication of the TRL scale gradually diminished as its usage spread outside its original context (space programs)".
The European Commission advised EU-funded research and innovation projects to adopt the scale in 2010. TRLs were consequently used in 2014 in the EU Horizon 2020 program. In 2013, the TRL scale was further canonized by the ISO 16290:2013 standard. A comprehensive approach and discussion of TRLs has been published by the European Association of Research and Technology Organisations (EARTO). Extensive criticism of the adoption of TRL scale by the European Union was published in The Innovation Journal, stating that the "concreteness and sophistication of the TRL scale gradually diminished as its usage spread outside its original context (space programs)".
Current NASA usage
The current nine-point NASA scale is:
- Level 1 – Basic principles observed and reported
 - Level 2 – Technology concept and/or application formulated
 - Level 3 – Analytical and experimental critical function and/or characteristic proof-of concept
 - Level 4 – Component and/or breadboard validation in laboratory environment
 - Level 5 – Component and/or breadboard validation in relevant environment
 - Level 6 – System/subsystem model or prototype demonstration in a relevant environment (ground or space)
 - Level 7 – System prototype demonstration in a space environment
 - Level 8 – Actual system completed and “flight qualified” through test and demonstration (ground or space)
 - Level 9 – Actual system “flight proven” through successful mission operations
 
History
Technology
 Readiness Levels were originally conceived at NASA in 1974 and formally
 defined in 1989. The original definition included seven levels, but in 
the 1990s NASA adopted the current nine-level scale that subsequently 
gained widespread acceptance.
Original NASA TRL Definitions (1989)
- Level 1 – Basic Principles Observed and Reported
 - Level 2 – Potential Application Validated
 - Level 3 – Proof-of-Concept Demonstrated, Analytically and/or Experimentally
 - Level 4 – Component and/or Breadboard Laboratory Validated
 - Level 5 – Component and/or Breadboard Validated in Simulated or Realspace Environment
 - Level 6 – System Adequacy Validated in Simulated Environment
 - Level 7 – System Adequacy Validated in Space
 
The TRL methodology was originated by Stan Sadin at NASA Headquarters in 1974.
 At that time, Ray Chase was the JPL Propulsion Division representative 
on the Jupiter Orbiter design team. At the suggestion of Stan Sadin, Mr 
Chase used this methodology to assess the technology readiness of the 
proposed JPL Jupiter Orbiter spacecraft design.
 Later Mr Chase spent a year at NASA Headquarters helping Mr Sadin 
institutionalize the TRL methodology. Mr Chase joined ANSER in 1978, 
where he used the TRL methodology to evaluate the technology readiness 
of proposed Air Force development programs. He published several 
articles during the 1980s and 90s on reusable launch vehicles utilizing 
the TRL methodology.
 These documented an expanded version of the methodology that included 
design tools, test facilities, and manufacturing readiness on the Air 
Force Have Not program.
 The Have Not program manager, Greg Jenkins, and Ray Chase published the
 expanded version of the TRL methodology, which included design and 
manufacturing. Leon McKinney and Mr Chase used the expanded version to assess the 
technology readiness of the ANSER team's Highly Reusable Space 
Transportation ("HRST") concept. ANSER also created an adapted version of the TRL methodology for proposed Homeland Security Agency programs.
The United States Air Force adopted the use of Technology Readiness Levels in the 1990s.
In 1995, John C. Mankins, NASA, wrote a paper that discussed NASA's use of TRL, extended the scale, and proposed expanded descriptions for each TRL. In 1999, the United States General Accounting Office produced an influential report that examined the differences in technology transition
 between the DOD and private industry. It concluded that the DOD takes 
greater risks and attempts to transition emerging technologies at lesser
 degrees of maturity than does private industry. The GAO concluded that 
use of immature technology increased overall program risk. The GAO 
recommended that the DOD make wider use of Technology Readiness Levels 
as a means of assessing technology maturity prior to transition. In 
2001, the Deputy Under Secretary of Defense for Science and Technology 
issued a memorandum that endorsed use of TRLs in new major programs. 
Guidance for assessing technology maturity was incorporated into the Defense Acquisition Guidebook. Subsequently, the DOD developed detailed guidance for using TRLs in the 2003 DOD Technology Readiness Assessment Deskbook. 
Because of their relevance to Habitation, 'Habitation Readiness 
Levels (HRL)'  were formed by a group of NASA engineers (Jan Connolly, 
Kathy Daues, Robert Howard, and Larry Toups). They have been created to 
address habitability requirements and design aspects in correlation with
 already established and widely used standards by different agencies, 
including NASA TRLs.
In the European Union
The European Space Agency adopted the TRL scale in the mid-2000s. Its handbook
 closely follows the NASA definition of TRLs. The universal usage of TRL
 in EU policy was proposed in the final report of the first High Level 
Expert Group on Key Enabling Technologies, and it was indeed implemented in the subsequent EU framework program, called H2020, running from 2013 to 2020.[1] This means not only space and weapons programs, but everything from nanotechnology to informatics and communication technology.
The TRLs in Europe are as follows:
- TRL 1 – Basic principles observed
 - TRL 2 – Technology concept formulated
 - TRL 3 – Experimental proof of concept
 - TRL 4 – Technology validated in lab
 - TRL 5 – Technology validated in relevant environment (industrially relevant environment in the case of key enabling technologies)
 - TRL 6 – Technology demonstrated in relevant environment (industrially relevant environment in the case of key enabling technologies)
 - TRL 7 – System prototype demonstration in operational environment
 - TRL 8 – System complete and qualified
 - TRL 9 – Actual system proven in operational environment (competitive
 manufacturing in the case of key enabling technologies; or in space)
 
Assessment tools
A Technology Readiness Level Calculator was developed by the United States Air Force. This tool is a standard set of questions implemented in Microsoft Excel
 that produces a graphical display of the TRLs achieved. This tool is 
intended to provide a snapshot of technology maturity at a given point 
in time.
The Technology Program Management Model was developed by the United States Army.
 The TPMM is a TRL-gated high-fidelity activity model that provides a 
flexible management tool to assist Technology Managers in planning, 
managing, and assessing their technologies for successful technology 
transition.  The model provides a core set of activities including systems engineering and program management
 tasks that are tailored to the technology development and management 
goals.  This approach is comprehensive, yet it consolidates the complex 
activities that are relevant to the development and transition of a 
specific technology program into one integrated model.
Uses
The primary 
purpose of using technology readiness levels is to help management in 
making decisions concerning the development and transitioning of 
technology. It should be viewed as one of several tools that are needed 
to manage the progress of research and development activity within an 
organization.
Among the advantages of TRLs:
- Provides a common understanding of technology status
 - Risk management
 - Used to make decisions concerning technology funding
 - Used to make decisions concerning transition of technology
 
Some of the characteristics of TRLs that limit their utility:
- Readiness does not necessarily fit with appropriateness or technology maturity
 - A mature product may possess a greater or lesser degree of readiness for use in a particular system context than one of lower maturity
 - Numerous factors must be considered, including the relevance of the products' operational environment to the system at hand, as well as the product-system architectural mismatch
 
Current TRL models tend to disregard negative and obsolescence 
factors. There have been suggestions made for incorporating such factors
 into assessments.
For complex technologies that incorporate various development 
stages, a more detailed scheme called the Technology Readiness Pathway 
Matrix has been developed going from basic units to applications in 
society. This tool aims to show that a readiness level of a technology 
is based on a less linear process but on a more complex pathway through 
its application in society. 
