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Navigating Space Nuclear Safety: The Role of the Nuclear Regulatory Commission

Navigating Space Nuclear Safety: The Role of the U.S. Nuclear Regulatory Commission

Expedition 49 crew members capture a nighttime view of the Strait of Gibraltar with a Russian Soyuz spacecraft (left) and Progress spacecraft (right) in the foreground.
Image credit: https://www.nasa.gov/image-article/nighttime-view-of-strait-of-gibraltar/

 

Space nuclear systems have contributed to remarkable progress in U.S. missions. These systems include the radioisotope thermoelectric generators (RTGs) that power the Mars rovers Curiosity and Perseverance and that will power the upcoming Dragonfly probe to Saturn’s moon Titan. These endeavors underscore the critical role of nuclear technologies in space exploration. RTGs, which use the heat from radioactive decay to generate electricity, have been a reliable power source for spacecraft and planetary rovers since the 1960s, enabling missions to venture into the far reaches of our solar system where solar panels become less effective.

The U.S. Nuclear Regulatory Commission (NRC) plays a role in ensuring the safe and responsible use of nuclear technologies in space missions. The NRC collaborates with experts and other U.S. government agencies to review the safety of these missions. Equipped with the U.S. Department of Energy’s (DOE’s) modern Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), the National Aeronautics and Space Administration’s (NASA’s) Mars Science Laboratory rover Curiosity has successfully explored the Martian surface, conducted experiments, and transmitted valuable data back to Earth since its arrival to the planet in 2012. The NASA Mars 2020 rover Perseverance, which landed on the planet in 2021 with its own MMRTG, continues this legacy, conducting cutting-edge experiments and paving the way for future human missions to Mars. 

In the coming years, space nuclear systems will continue to power critical space missions, with three significant milestones planned for launch in 2028. The NASA Dragonfly probe will demonstrate the potential of new types of nuclear-powered vehicles for navigating and investigating distant celestial bodies, such as its destination, Titan. The Rosalind Franklin Mars rover, which is part of the European Space Agency’s ExoMars program but will launch from NASA’s Kennedy Space Center in Florida, will search for past life with its landing system aided by a radioisotope heater unit—similar to an RTG, but used just to keep temperature-sensitive components warm. The agency also plans to reenter the field of space nuclear reactors with Space Reactor-1 (SR-1) Freedom. The craft will use the electrical energy generated by its reactor, rather than the chemical energy of rocket fuel, to power the engine and propel the craft to Mars—an arrangement called nuclear electric propulsion. Data from the SR-1 mission will inform a lunar-adapted system, Lunar Reactor-1, intended to spearhead a new era for nuclear power in outer space. The NRC has joined and will continue to join with other agencies to review the safety analyses of these missions as part of the launch approval process for spacecraft equipped with nuclear material.

NASA Dragonfly Mission

European Space Agency ExoMars Rover (Rosalind Franklin)

NASA SR-1 Freedom Mission 

Dragonfly Mission Overview Dragonfly mission concept of entry, descent, landing, surface operations, and flight at Titan.
Image credit: https://astrobiology.nasa.gov/news/nasa-announces-astrobiology-mission-to-titan/

 

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What Is the NRC’s Role in Space Nuclear Safety?


Image credit: https://www.jpl.nasa.gov/news/next-mars-rover-will-have-23-eyes

As space missions progress, the NRC collaborates with other nuclear-involved agencies (see “What Is the Interagency Nuclear Safety Review Board?” on this page) to provide advice for the safety of space nuclear systems. In past U.S. missions, these systems have predominantly taken the form of RTGs, but SR-1 will mark the return of nuclear reactors to space, which last flew on a U.S. spacecraft in 1965. The DOE, NASA, and U.S. Department of Defense (DoD) set requirements that must be adhered to during the design, construction, and operation of nuclear‑powered space systems. These requirements build upon recommendations made in international guidance from the United Nations and the International Atomic Energy Agency.

The NRC also reviews and approves the terrestrial handling, transportation, and storage of radioactive materials that may be used in space nuclear activities. The NRC’s expertise in consequence analysis may be called on to review the safety of the launch and other mission activities that may have terrestrial consequences, ensuring that radioactive materials are safely managed to protect the environment and public health. The NRC regularly communicates with stakeholders and stays abreast of technological advancements, keeping pace with developments in space nuclear activities to ensure the safety of nuclear systems launched into Earth orbit and beyond.

NRC Materials Transportation

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What Is the Interagency Nuclear Safety Review Board?

The Interagency Nuclear Safety Review Board (INSRB) is responsible for assessing the safety of space nuclear system launches sponsored by U.S. government agencies. It serves as a coordinating body, bringing together experts from seven Federal agencies for prelaunch safety reviews of proposed space nuclear missions. The INSRB conducts independent safety reviews to evaluate a mission’s safety analysis report and inform launch authorities of its quality before a launch decision is made; the board does not provide a recommendation for or against launch. The INSRB includes representatives from the DoD, DOE, U.S. Department of State, U.S. Department of Transportation (through the Federal Aviation Administration (FAA)), U.S. Environmental Protection Agency, NASA, and the NRC. The board leverages the collective expertise of its member agencies in its critical role as the evaluator of safety analysis report quality and informing the launch approval decision for space nuclear systems.

Commercially sponsored missions that may include a space nuclear system are licensed like any other commercial space launch. Sponsors send applications to the FAA Office of Commercial Space Transportation. Unlike government-sponsored space nuclear system launches, for which it contributes to the safety review as one of several agencies, the FAA takes on the primary role for commercial launches, though it may still choose to consult interagency partners, such as the NRC.

NASA Office of Safety and Mission Assurance Nuclear Flight Safety (contains useful information on INSRB guidance documents)

FAA Office of Commercial Space Transportation

NSPM-20 (establishes the INSRB)

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The Evolution of Space Nuclear Launch Safety: NSPM-20 and Interagency Cooperation

The NRC’s Office of Nuclear Regulatory Research has reviewed publicly available information on the history of the safety assessment and review process governing space nuclear system launches. One focus of the review is the transformative impact of National Security Presidential Memorandum 20 (NSPM-20). This literature review looks back at the origins of space nuclear systems and the need for safety reviews, focusing on sources relevant to space nuclear system launch safety reviews. The report discusses the history of the safety assessment process in the United States, listing possible accidents, responses, dispersion, exposure, and consequences and highlighting the limited environmental impact of the rare past space nuclear system incidents. The report details the evolution of the interagency review process, initially spearheaded by the DOE and the NRC’s shared predecessor, the Atomic Energy Commission, and culminating decades later in the issuance of NSPM-20 in 2019. NSPM-20 established the standing INSRB to replace the previously ad hoc, mission-specific Interagency Nuclear Safety Review Panel (INSRP).

NSPM-20 also introduced a tiered approach to launch approvals and a refined framework for interagency cooperation, with updated metrics reshaping the approach to space nuclear system launch approvals. Under this system, mission launches such as Dragonfly (with its RTG) or SR‑1 would require INSRB review before a launch decision due to the amount of nuclear material. In contrast, a mission like Rosalind Franklin, using only a smaller and less active radioisotope heater unit, would fall below that same criterion—it is not currently expected to need an INSRB review.

The NRC’s literature review also delves into our evolving role in this process, transitioning from an observer to an active participant, and the agency’s eventual membership in the INSRB. The review examines the balance between collaboration and independence in the review process, showcasing the significance of interagency review in enhancing the safety of space nuclear system launches.

NRC Research Information Letter 2023-006, “Literature Review: Safety Review Process for Space Nuclear System Launches”

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The NRC’s Role in NASA’s Mars 2020 Launch: Ensuring Safe Space Nuclear Activity

This image of the floor of Jezero Crater was taken by one of the Navcam imagers aboard NASA’s Perseverance Mars rover on Feb. 5, 2023, the 698th Martian day, or sol, of the mission.
The MMRTG is the finned white cylinder in the center of this photo.
Image credit: https://mars.nasa.gov/resources/27314/looking-back-at-perseverances-second-science-campaign/

In 2016, Don Helton, now the Nuclear Flight Safety Officer at NASA, wrote about the NRC’s involvement with NASA in planning for the launch of the Mars 2020 mission through the INSRP. The Mars 2020 mission was a part of NASA’s Mars Exploration Program to address key questions about potential ancient life and demonstrate technologies for future human expeditions. The NRC’s role in this interplanetary endeavor derives from the mission’s MMRTG, which uses the radioactive decay of plutonium to produce electrical power for the rover and its instruments. The NRC participated in the Mars 2020 INSRP as a technical advisor to review the safety analysis of the launch. The panel evaluated potential radiological hazards and risk mitigation methods while reviewing the safety analysis report for the mission, producing a safety evaluation report to inform the launch authorization decision.

The NRC has previously played similar roles in other NASA launches. More information on the Mars 2020 mission can be found on NASA’s website and in the final environmental impact statement.

NASA Mars 2020: Perseverance Rover

NRC’s Supporting Role in NASA’s Mars 2020 Launch

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Regulatory Information Conference 2021, 2023, and 2025 Space Nuclear Sessions

The NRC’s Regulatory Information Conference (RIC) in 2021, 2023, and 2025 included sessions on space nuclear missions, highlighting the NRC’s commitment to the safe use of nuclear materials beyond Earth’s boundaries. The sessions provided a platform for experts and NRC employees to engage in meaningful dialogue, share insights, and collaborate on space nuclear power systems. RIC 2021 Session W19, “Space Nuclear Power Systems—To Cislunar and Beyond!”, showcased how nuclear energy can sustainably power spacecraft during long‑distance space exploration. In RIC 2023 Session T1, “Beyond Earth: The Future of Nuclear Technology in Space,” discussions continued to explore nuclear power’s potential in space missions. Most recently, in RIC 2025 Session TH24, “One Giant Leap for Humankind: Using Nuclear Power to Explore Space,” speakers highlighted efforts in returning nuclear reactors to U.S. space missions. NRC personnel have actively participated in safety assessments and technology evaluation to ensure responsible and safe space nuclear activities. The NRC’s dedication to supporting cutting-edge research and safe nuclear technology applications in space demonstrates its commitment to humanity’s quest to venture beyond Earth’s boundaries.

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References

 

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Page Last Reviewed/Updated Thursday, August 20, 2026

Page Last Reviewed/Updated Thursday, August 20, 2026