Technology readiness levels, explained

A technology readiness level (TRL) is a number from 1 to 9 that states how mature a technology is, based on where and how it has been demonstrated. In a technology readiness assessment (TRA), the Department of Defense (DoD) assigns a TRL to each critical technology element (CTE), the new or novel technology a system depends on, "with 9 representing the most mature." The February 2025 Technology Readiness Assessment Guidebook from the Office of the Under Secretary of Defense for Research and Engineering gives DoD's definitions. The guidebook stresses that TRLs are not a measure of design validity. They record maturity at the time of measurement.

The nine levels in DoD's words

The guidebook's Table 2-1 gives the hardware definitions:

TRL	DoD definition (hardware)
1	Basic principles observed and reported.
2	Technology concept and/or application formulated.
3	Analytical and experimental critical function and/or characteristic proof of concept.
4	Component and/or breadboard validation in a laboratory environment.
5	Component and/or breadboard validation in a relevant environment.
6	System/subsystem model or prototype demonstration in a relevant environment.
7	System prototype demonstration in an operational environment.
8	Actual system completed and qualified through test and demonstration.
9	Actual system proven through successful mission operations.

Table 2-2 gives software levels with similar definitions but different examples and evidence. The guidebook defines a relevant environment as a testing environment that "simulates both the most important and most stressing aspects" of the operational environment. Both TRL 5 and TRL 6 depend on it. One or a few demonstrations under the most favorable conditions are not enough. The step from TRL 6 to TRL 7 is a change of scale, from a representative model or prototype to a prototype of the planned system in the operational environment. At Milestone C, the guidebook says, CTEs should be able to achieve TRL 7.

Where the scale came from

Three official accounts of the origin differ in their dates.

• DoD's 2025 guidebook says the TRL was first developed at the National Aeronautics and Space Administration (NASA) in the 1970s.
• The Government Accountability Office (GAO), in its January 2020 guide, says a NASA researcher pioneered the first scale in 1974 with seven levels, which were not formally defined until 1989.
• NASA's own TRA Best Practices Guide, whose NASA record gives a June 30, 2020 publication date, says the levels were first described at NASA headquarters in the 1980s.

The DoD guidebook adds that DoD formally endorsed TRLs in 2001, produced a TRA Deskbook in 2003, and revised it in 2005, 2009, and 2011. NASA's guide says a TRL of 6 or higher is typically required before a technology is integrated into a flight system. NASA's public TRL page shows NASA's flight focus at the top of the scale: TRL 7 requires demonstration in a space environment, and TRL 9 means "flight proven" during a successful mission.

Milestone B: from certification to factor

10 U.S.C. 4252 governs Milestone B for major defense acquisition programs. Public Law 118-159, enacted December 23, 2024, changed the section heading from "certification required before" to "factors to be considered before" Milestone B approval, rewrote the list, and struck the former waiver subsection. Factor (b)(2) now reads that the technology "has been demonstrated in a relevant environment." The milestone decision authority must confirm that the factors were considered and issue a written record of decision, which goes to the congressional defense committees within 15 days.

The statute names an environment, not a number. The guidebook supplies the number: an appendix describes TRL 6 as "required for approval at Milestone B." The February 2025 edition's change record says it was updated for the section 4252 changes, removing references to waivers and certifications. GAO's 2020 guide, written under the older law, describes the milestone decision authority certifying TRL 6 before Milestone B.

GAO's best-practice guide

GAO published GAO-20-48G on January 7, 2020, and its report page notes a reissue with revisions on February 11, 2020. The guide names four characteristics of a high-quality TRA: credible, objective, reliable, and useful. The guide's five steps are to prepare the TRA plan and select the team, identify the critical technologies, assess them, prepare the TRA report, and use the report's findings.

GAO goes one level further than DoD on timing. The guide recommends that critical technologies reach TRL 7 at the decision to start system development, and accepts TRL 6 in special cases, such as space, where operational testing is impractical. DoD's guidebook draws on GAO's guide but notes that, unlike DoD policy, the guidebook itself is not mandatory. The guidebook also says TRA team members should be independent of the program office and of the chain of command between that office and the milestone decision authority.

What to check

• Which CTEs did the assessment identify, and what evidence supports the TRL assigned to each?
• Does a TRL 6 claim rest on a relevant environment that simulates the most stressing conditions, or on a few favorable demonstrations?
• Does a TRL 7 claim show a prototype of the planned system in an operational environment?
• Was software assessed against the software definitions in Table 2-2?
• Which guidebook edition was used, and does the document still describe a Milestone B certification or waiver that the 2024 law removed?
• Were the assessors independent of the program office and its chain of command to the milestone decision authority?

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Sources

1. 1Technology Readiness Assessment Guidebook · Office of the Under Secretary of Defense for Research and Engineering, February 2025
2. 2United States Code, 2024 Edition, Title 10, Section 4252 - Major defense acquisition programs: factors to be considered before Milestone B approval · U.S. Government Publishing Office
3. 3GAO-20-48G, Technology Readiness Assessment Guide: Best Practices for Evaluating the Readiness of Technology for Use in Acquisition Programs and Projects · U.S. Government Accountability Office, January 7, 2020
4. 4Technology Readiness Assessment Guide (GAO-20-48G), accessible version · U.S. Government Accountability Office, January 2020
5. 5Technology Readiness Assessment Best Practices Guide (SP-20205003605) · NASA Office of the Chief Technologist, NTRS record dated June 30, 2020
6. 6Technology Readiness Levels · NASA Space Communications and Navigation Program

Where this shows up in our work

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