This article has been revised to reflect NASA's updated plan for PROMISE to be a hybrid of both the Perseverance and Curiosity engineering testbeds, rather than the Perseverance testbed alone. The cost estimate is unchanged.

In a surprise announcement on June 30, 2026, NASA Administrator Jared Isaacman stated that the agency may send an engineering duplicate of a Mars rover to the Moon.

“We've got this hardware that the taxpayers invested a lot in,” said Isaacman. “So the question was posed, what if we sent it to the Moon?”

NASA did not clarify which scientific priorities this project would address or how it would be funded given the 46% cuts currently proposed to the agency’s Science Mission Directorate.

NASA's Jet Propulsion Laboratory (JPL) maintains two engineering duplicates of the Mars rovers Curiosity and Perseverance on its campus in southern California. 

The concept, called PROMISE (Polar Rover for Observation, Mapping, and In-Situ Exploration), would assemble a rover from the body and parts of these engineering test articles for use at the Moon.

PROMISE is presented as a sensible, cost-saving effort to repurpose existing hardware for lunar exploration. It’s a worthy experiment, certainly, but the outcome is far from certain. Qualifying a testbed rover for the rigors of spaceflight will take considerable time and money, particularly since NASA describes PROMISE as using components that could be upwards of 17 years old. Given these complexities, if NASA decides to pursue this project, PROMISE would likely cost the agency between $700 million and $1.3 billion and not launch until sometime in the early 2030s.

To reach this conclusion, I analyzed historical spending on prior missions, NASA procedural requirements, and detailed cost estimates for nuclear-powered lunar rovers done for the most recent planetary science decadal survey.

This is, emphatically, not a replacement for a detailed engineering cost assessment. That effort is currently underway at NASA's Jet Propulsion Laboratory. Instead, this estimate attempts to define a reasonable cost range based on known requirements: launch costs, spacecraft processing and assembly, mission operations, nuclear power compliance, and science payload development. These quickly add up to hundreds of millions before any hardware upgrades are considered. If nothing else, PROMISE represents a significant opportunity cost that should to be weighed against the declines in overall science funding and the drawdown of investment at Mars and beyond.

Regardless of whether one agrees with every estimate below, one thing is clear: PROMISE is far from a “freebie.” It will consume significant resources that might otherwise be available to pursue established scientific priorities in NASA's scientific portfolio.

NASA maintains an engineering duplicate (not a one-to-one "copy" of flight hardware) of both its Curiosity and Perseverance Mars rovers, each with access to a simulated Martian landscape (the "Mars Yard" at JPL). These are used to test procedures and drive paths, and to help troubleshoot any hardware issues with the active spacecraft. 

Perseverance's testbed rover, named OPTIMISM, was deployed in 2021 and has the same size and characteristics as the Martian variant: it carries avionics, a computer, drive cameras, and a sampling system. MAGGIE is the testbed rover for the Curiosity mission and has been in use since 2009.

Repurposing old hardware is not uncommon at NASA, even for space science missions. The Phoenix spacecraft, which was selected through an open and competitive scientific selection process, landed in the northern polar region of Mars in 2008, and reused 70% of its mission hardware from an earlier lander mission canceled in 2000. But, unlike the OPTIMISM testbed rover, Phoenix reused hardware originally built to fly in space that had been stored in a cleanroom. According to NASA's own reporting, reuse succeeded because the hardware had been stored in a clean and safe environment with detailed documentation describing its fabrication and testing. Even then, the mission cost approximately $640 million (when adjusted for inflation to fiscal year 2025 dollars), exceeding the project's original cost cap by nearly 40%.

PROMISE is proposing to reuse engineering hardware that was not stored in a cleanroom, but in a garage next to the Mars Yard in the JPL campus in Pasadena. They were never intended for spaceflight. There are no examples of NASA successfully leveraging non-flight-qualified hardware for a major science mission on this scale.

PROMISE would weigh about 1,000 kg, exceeding the delivered payload mass  limits of all of NASA's commercial lunar delivery partners save one, Blue Origin. The company's forthcoming Blue Moon Mark 1 lander advertises a landing payload of up to 3,000 kg, and already has a NASA contract to deliver the agency's ~950 kg Lunar Terrain Vehicle for Artemis astronauts. That contract is valued at up to $234 million per delivery.

For comparison, SpaceX's Falcon Heavy launch contract for NASA's plutonium-powered Dragonfly spacecraft is worth $256 million. Astrobotic's Griffin CLPS contract sets the high-end potential delivery cost at $320 million.

These estimates may still be low. Since plutonium decays continuously, it continuously gives off heat. That heat has to go somewhere while the spacecraft is en route to the Moon. The Mark 1 may require modifications to handle this situation. Other ground equipment modifications may be required to facilitate loading of the plutonium power source and to meet additional safety requirements for payload processing.

New Glenn, the only rocket designed to launch Blue Origin's Mark 1 lander, is currently grounded due to a pad explosion earlier this year. Absent a launch vehicle databook with credible failure statistics, NASA cannot complete the safety analysis required to launch nuclear material, a process that can take years.

There have been some rumors that the Mark 1 could be retrofitted onto a Starship booster or Falcon Heavy, but that would require significant engineering work and likely require new ground support structures for SpaceX hardware, at a minimum. And this novel launch configuration would still need to complete its own safety review before launching PROMISE. The costs of this are unknown, but certainly far from zero.

The Perseverance rover is powered by 4.8 kg 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.

There is a limited quantity of Pu-238 for use by NASA, which is managed by the Department of Energy (DOE). For the past 15 years, NASA has paid the DOE to produce more Pu-238 and grow its stockpile, a process that has fallen behind its production targets. The White House's FY 2027 budget request proposes to end NASA's radioisotope power program in the coming years.

The OPTIMISM testbed rover doesn't need to worry about nuclear safety; it gets its power from the electrical grid. But PROMISE would require 4.8 kg of plutonium-238 fuel to explore the Moon and survive the bitter cold environment of two-week-long lunar nights.

Using plutonium power, however, triggers expensive and time-consuming environmental and safety reviews. According to a 2019 study by the Science Technology & Policy Institute, the reviews themselves cost tens of millions of dollars and take, on average, more than six years to complete. A Presidential memorandum in 2019 attempted to streamline some of these review processes for launching nuclear material, but it still requires a lengthy safety review process.

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 I use as the low-end estimate.

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.

While no science goals were discussed for the PROMISE mission in the announcement or press release, we got a hint of NASA's thinking from NASA's Moon base program manager, Carlos García-Galán, highlighting the value of "long traverses getting into those very hard-to-reach areas" on the lunar surface.

The planetary science decadal survey recommended a lunar rover mission for this very purpose, called Endurance-A. The concept was to design a mid-sized (about 500 kg) rover that could travel thousands of kilometers and explore hazardous areas of the Moon that no astronaut could visit. It would collect lunar samples and then drive them back to a lunar base to be unloaded and prepared for Earth return by astronauts.

The Endurance-A mission concept was developed in detail for the decadal survey process. I use the reported Endurance-A science payload costs as our high estimate. To get a low estimate, I averaged comparative payload contract costs for CLPS science instruments as reported in public contract data, which came out to roughly $50 million.

The scientific community has continued to study opportunities for exploration at the Moon, and recently re-affirmed support for an Endurance-A-like mission with the capability to travel thousands of kilometers on the lunar surface.

This is, admittedly, the most uncertain variable, and my estimate is appropriately broad. PROMISE currently has no mission goals or operational requirements that allow us to constrain this work. The actual engineering assessment itself will provide details on what's usable, what's not, what needs to be replaced, and what needs to be tested in order to qualify for flight.

So I took a different approach and compared the integration and assembly portions of recent lunar missions to set our high and low bounds. For the low-end scenario, I used the VIPER mission, NASA's smaller, simpler, solar-powered lunar rover awaiting launch next year.

VIPER entered its final assembly, integration, and testing phase in June 2023. NASA planned to spend $235 million in this period (annual expenditures, adjusted for inflation, during this phase, plus an additional $84 million to prepare for a late 2025 launch). This represents a best-case scenario, in which little to no new engineering design is required, the necessary pieces are functionally assembled together without incident, and testing reveals no serious issues.

NASA has stated that there is flight-spare hardware available. These are of much higher pedigree than what is used on the testbed rover, and could genuinely help keep costs on the lower side. But they still require verification, integration, and qualification work.

For the high-end estimate, I use the Phase A-D (design, build, integration, and test) estimates from the Endurance-A mission, minus the radioisotope and science instrument costs already accounted for earlier.

Based on this analysis, I believe we can draw the following conclusions from the PROMISE concept at this early stage:

• Repurposing NASA's Mars rover testbeds for the Moon would cost many hundreds of millions of dollars; likely more. There is no plausible version of this mission that is "free," and even the low-end cost is equivalent to a small- to mid-size planetary exploration mission.
• The use of radioisotope power has extensive monetary and schedule cost.  Even an expedited safety review faces significant hurdles given the current state of Blue Origin's New Glenn rocket and development status of the Mark 1 lander.
• PROMISE would consume an MMRTG currently reserved for a future competed science mission. It will also draw plutonium from a dwindling national stockpile. 
• A 2028 launch is not credible. The nuclear paperwork alone suggests that the early 2030s are more reasonable. The technical uncertainties of converting an engineering test article into a spaceflight vehicle also add uncertainty to the schedule.
• Converting a testbed rover removes a capability from projects that still use them. JPL built testbed rovers for a reason: you don't get second chances on Mars. They help prevent accidents before they happen, and removing that increases the risk to Perseverance. These consequences could be mitigated if one testbed is still functional.
• Should PROMISE move forward, the best-case science scenario is to adopt the goals of the Endurance-A mission concept where possible. It's not clear if this hardware could travel the thousands of kilometers proposed for Endurance-A, but it could carry a subset of the scientific payload. This would address some decadal priorities and leverage the unique capabilities of this hardware.

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