Radioisotope power system and compliance: $78 million – $117 million [confidence: high]
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.
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.
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.
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.
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.
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.
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.
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.