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


Space nuclear systems have contributed to remarkable progress in U.S. missions. These systems include the radioisotope thermoelectric generators (RTG) that powered Mars Science Lab 2011, Mars 2020, and that will power the upcoming Dragonfly probe to 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 are not effective.

The 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 Department of Energy (DOE)’s modern Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), the National Aeronautics and Space Administration (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’s 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. 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, a moon of Saturn. The Department of Defense (DoD)’s Demonstration Rocket for Agile Cislunar Operations (DRACO) program is pioneering the development of a modern nuclear reactor-powered rocket engine offering extended propulsion capabilities for deep-space missions. 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 launches of spacecraft equipped with nuclear material.


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What is the NRC's Role in Space Nuclear Safety?

As space missions progress, the NRC collaborates with other nuclear-involved agencies (see “What is the Interagency Nuclear Safety Review Board?” on this page) on advice for the safety of nuclear power sources in spacecraft. Historically, these have taken the form of RTGs, but new development projects may lead to the return of nuclear reactors to space, last used by a U.S. spacecraft in 1965. The DOE, NASA, and 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.

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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 conducted by U.S. government agencies. It serves as a coordinating body, bringing together experts from seven federal agencies for pre-launch safety reviews of proposed space nuclear missions. The INSRB will conduct independent safety reviews to evaluate the quality of a mission’s safety analyses and inform launch authority leaders of the quality of safety evaluations before a launch decision is made. The INSRB includes representatives from the DoD, DOE, Department of State, Department of Transportation, Environmental Protection Agency, NASA, and the NRC. The board leverages the collective expertise of its member agencies for its critical role in evaluating the safety of nuclear technologies in space missions and informing the launch approval decision.

NASA Office of Safety and Mission Assurance

Nuclear Flight Safety webpage has useful information on INSRB guidance documents, and link to NSPM-20 establishing 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 launch safety reviews. The report discusses the history of the safety assessment process in the U.S., 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, having been spearheaded initially by the DOE and the NRC’s predecessor, the Atomic Energy Commission, 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 launch approvals. The NRC’s literature review also delves into our evolving role in this process, transitioning from an observer to an active participant, and eventual membership in 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’s Research Information Letter report, "Literature Review: Safety Review Process for Space Nuclear System Launches."

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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:

In 2016, Don Helton, now NASA Nuclear Flight Safety Officer, wrote about the NRC’s involvement with NASA in planning for the launch of the Mars 2020 mission through 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 using an 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 of 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 the Final Environmental Impact Statement.

Former NRC staff person (now at NASA) Don Helton's NRC blog post about Mars 2020

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Regulatory Information Conference 2021 & 2023 Space Nuclear Sessions

The NRC’s Regulatory Information Conference (RIC) in 2021 and 2023 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. 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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Page Last Reviewed/Updated Friday, October 20, 2023