Rad-hard (radiation-hardened)
Electronics built to minimize radiation effects from the outset-at the process (RHBP) and/or design (RHBD) level. These parts are typically developed to military/space standards and are accompanied by formal Radiation Hardness Assurance (RHA) ratings. For example, under MIL-PRF-38535 microcircuits carry RHA letter grades such as R = 100 krad(Si), F = 300 krad(Si), H = 1 Mrad(Si).
Hardening at the process/design level
Techniques often include SOI, specialized oxides, layout guard rings, and architectural redundancy such as TMR-i.e., RHBP/RHBD approaches. Specific implementations vary by device and process, and terminology differs across references. NASA materials also use “hardening” consistently to mean process- and design-level approaches.
Formal RHA rating
Under MIL-PRF-38535, microcircuits may carry an RHA letter grade indicating guaranteed TID tolerance (e.g., R = 100 krad(Si), F = 300 krad(Si), H = 1 Mrad(Si)). These markings appear similarly in DLA/NASA documentation. Note that this does not automatically cover all SEE behavior-SEE must be verified with separate data and tests.
Application of test standards
TID evaluations typically follow MIL-STD-883, TM1019, including ELDRS considerations. Reports or SMDs that include TM1019-based results are helpful when judging credibility.
Rad-tolerant (radiation-tolerant)
Electronics that are not fully hardened but are made to withstand radiation to an acceptable level via a mix of design, process, architecture, and operational mitigations. NASA materials describe this in practice as electronics where radiation effects are addressed and mitigated by design. There is no single global numeric threshold that defines rad-tolerant.
Caveats
Unlike rad-hard, there is no universally accepted numeric cutoff (e.g., 100 krad or more). In real projects, teams should confirm TID/DDD/SEE levels against the RHA plan tailored to mission environment and lifetime. NASA’s RHA guidance emphasizes this process-centric approach.
System perspective
NASA’s RHA guidance highlights system-level tolerance as a core activity. Even if a component is labeled rad-tolerant, reliable operation typically also requires system-level mitigations such as ECC, TMR, scrubbing, and supply protection.
Conclusion
[1] U.S. Department of Defense, MIL-PRF-38535: Performance Specification, Integrated Circuits (Microcircuits) Manufacturing, General Specification for, Defense Logistics Agency (DLA), Fort Belvoir, VA, USA, 2021.
[2] U.S. Department of Defense, MIL-STD-883: Test Method Standard, Microcircuits, Method 1019, “Ionizing Radiation (Total Dose) Test Procedure,” 2020.
[3] NASA, “EEE-INST-002: Instructions for EEE Parts Selection, Screening, Qualification, and Derating,” NASA Office of Safety and Mission Assurance, Washington, DC, USA, Rev. D, 2019.
[4] D. A. Pellish, “Radiation Engineering for Designers,” NASA Radiation Effects and Analysis Group (REAG) Training Material, NASA Goddard Space Flight Center, Greenbelt, MD, USA, 2018.
[5] NASA, “Radiation Hardness Assurance (RHA) Standard Development and Guidelines,” NASA Electronic Parts and Packaging (NEPP) Program / NASA Engineering and Safety Center (NESC), Technical Presentation, 2020.
[6] European Cooperation for Space Standardization (ECSS), ECSS-Q-ST-60-15C, Space Product Assurance - Radiation Hardness Assurance - EEE Components, ESA Requirements and Standards Division, Noordwijk, The Netherlands, 2013.