Commercial Off-The-Shelf parts are a reality for virtually every modern space program. The economics are clear, rad-hard alternatives (when they exist) can cost 10-100× more and have lead times measured in months. But using COTS means accepting some radiation risk, and the question is how to assess and manage that risk intelligently.
Here’s a framework that works for many programs. Interested to hear how others approach it.
Step 1: Define your environment quantitatively. You can’t assess risk without knowing the threat. Get a proper environment definition — trapped protons, trapped electrons, solar protons (with a stated confidence level for SPEs), and GCR. Define it behind your actual shielding, not just in free space. Sector analysis or Monte Carlo transport through your CAD model is better than simple aluminum slab equivalent calculations.
Step 2: Prioritize your parts list. Not every COTS part needs the same level of attention. Analog and mixed-signal parts (voltage regulators, ADCs, op-amps) are almost always the most TID-sensitive. FPGAs, processors, and memory are the SEE concern. Passive components (resistors, standard capacitors) are generally not a radiation concern at typical mission doses. Focus your effort on the parts that matter.
Step 3: Search for existing data. Before testing anything, search the published literature, the NASA radiation databases, and NSREC Data Workshop proceedings. Many common COTS parts have been characterized by someone. But verify the data relevance — same manufacturer, similar date code, compatible test conditions.
Step 4: Test what you must. For radiation-critical parts without adequate heritage data, there’s no substitute for testing. The key decision is how much testing: full characterization (expensive, thorough) vs. screening at the requirement level (cheaper, answers go/no-go but doesn’t give you margins).
Step 5: Document your risk acceptance. For every COTS part, you need a story: “We know the environment is X, we have evidence the part can handle Y, and here’s why we believe the risk is acceptable.” That evidence can be test data, heritage, analysis, or similarity — but it needs to exist and be documented.
What frameworks do your programs use? How do review boards receive COTS risk arguments? What’s the minimum evidence you’d accept for a non-critical COTS part?