Scalable Tritium Power Systems and Regulatory Flight Path for Nuclear-Powered CubeSats

City Labs is pioneering a new class of tritium-based power systems designed to enable long-duration CubeSat and small-spacecraft missions operating in environments where solar power is insufficient or unreliable. These systems include tritium betavoltaic batteries for low-power trickle charging, radioluminescent light sources, and scalable thermal and electrical generators such as Mini-Radioisotope Heater Units (Mini-RHUs) and Tritium Thermoelectric Generators (TTGs). This work summarizes the design, fabrication, and regulatory progression of City Labs’ tritium metal-hydride technology, as well as the development of a production-scale, fully automated tritium loading system engineered for uniformity, repeatability, and commercial safety compliance. In Q4 2024, City Labs submitted a payload evaluation request to the Federal Aviation Administration (FAA) under 14 CFR §450.43 for a CubeSat flight demonstration carrying tritium-powered NanoTritium™ betavoltaic cells. The mission was evaluated under the national nuclear launch framework established by NSPM-20 and classified as a Tier I nuclear payload, requiring deterministic safety analysis and bounding-dose assessments. In Q3 2025, the FAA issued a positive determination authorizing up to 10,000 Ci of tritium activity for flight, the first commercial Tier I approval for a nuclear-powered spacecraft. Conservative HotSpot modeling demonstrated that public exposure remains below 1 mrem for bounding launch and reentry scenarios, obviating the need for a Probabilistic Risk Assessment (PRA) and confirming full compliance with Tier I criteria. Together, the flight hardware, validated safety case, and regulatory authorization establish a repeatable commercial pathway for deploying long-lived nuclear power systems on small spacecraft. Future phases will advance Mini-RHUs and TTGs to support nighttime survival, deep-space sensing, and autonomous operations in environments beyond the practical reach of solar power.