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The Perseverance rover is powered by 4.8 kilograms of Plutonium-238 (Pu-238) oxide, a radioactive material that generates heat, which the power system turns into electricity. Pu-238 does not occur naturally in any useful quantity and decays with a half-life of 87.7 years. It must be actively and continuously produced.<\/p>\n
The United States has a limited quantity of Pu-238 (the exact amount is classified). The Department of Energy (DOE) manages this stockpile. For the past 15 years, NASA has paid the DOE to restart Pu-238 production and grow its stockpile, and now faces cancellation in the White House’s FY 2027 budget request.<\/p>\n
The OPTIMISM testbed rover doesn’t need to worry about nuclear safety; it gets its power from the electrical grid. But PROMISE would require Plutonium-238 to explore the Moon and survive the bitter cold environment of two-week-long lunar nights.<\/p>\n
Using Plutonium power, however, triggers a myriad of expensive and time-consuming environmental and safety reviews. According to a 2019 study by the Science Technology & Policy Institute, the reviews themselves add approximately $40 million to the cost of a mission and take, on average, 6.5 years to complete. The actual Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) hardware costs tens of millions more and takes years to procure.<\/p>\n
Conveniently, NASA contracted to build two flight-ready MMRTGs back in 2021. One is assigned to the upcoming Dragonfly mission to Titan. The other was intended to be made available for a potential outer planets mission as recommended by the planetary science decadal survey. Based on NASA’s public comments, this may be the “spare” RTG.<\/p>\n
So, how much does NASA save by not having to procure a new MMRTG? It’s hard to say, the contracts are not public. A 2017 report by the U.S. Government Accountability Office stated that using a single MMRTG added $77 million to a mission’s cost; using two added $94 million. A rough decomposition implies a marginal hardware cost of around $17 million for the MMRTG and fuel itself, with the remaining $60 million being the overhead of managing nuclear material. Adjusted for inflation to 2025 dollars, that amount comes to $78 million, which we use as our low-end estimate.<\/p>\n
A Presidential memorandum in 2019 attempted to streamline some of the review process for nuclear material, but it still requires an extensive safety review before a spacecraft is approved to launch. Dragonfly, the first nuclear-powered NASA mission to be developed after the streamlined process, has still taken nearly 6 years to complete this work.<\/p>\n
For the high end, I add 50% to the baseline cost to capture the uncertainty of a novel review process for a new commercial launch system and potential ground system safety and processing upgrades.<\/p>\n<\/div>\n