RTGs and the Plutonium-238 Shortage Impacting Space Missions

In recent years, space missions have become increasingly ambitious, demanding reliable power sources. One of the key elements ensuring long-term operation of spacecraft in deep space conditions is the radioisotope thermoelectric generator (RTG). However, their efficiency depends directly on the availability of plutonium-238, which is currently in short supply. This shortage threatens future research, including missions to the outer planets and asteroid exploration.

This article examines the current state of plutonium-238 production, its impact on space exploration programs, and possible solutions to this issue. Against the backdrop of growing energy needs for spacecraft, it is important to understand how the plutonium-238 deficit affects NASA’s and other space agencies’ plans, as well as the measures being taken to ensure uninterrupted supply of this critically important element.

• $40 million cost per 1 kg of plutonium-238
• 30 kg current global stock of plutonium-238
• $15 million U.S. investment in 2026 for plutonium-238 production

Plutonium-238: The Key Element for RTGs

Plutonium-238 is a critically important element for the operation of radioisotope thermoelectric generators (RTGs), which power space missions when solar panels become ineffective. RTGs have an efficiency of 7-8%, making them a reliable energy source for long-duration expeditions to distant regions of our Solar System, such as missions to Pluto and beyond. However, producing plutonium-238 involves significant costs: the price of one kilogram of this isotope reaches about $40 million, limiting its availability for space programs.

As of 2026, there are only 30 kg of plutonium-238 worldwide, far below the needs of NASA and other space agencies. For example, the planned NASA mission to Titan, Saturn’s moon, will require considerably more of this isotope than is currently available. The shortage of plutonium-238 threatens not only current but also future space projects.

Problems and Solutions

• Available plutonium-238 quantity: 30 kg
• Production cost: $40 million per kilogram
• RTG efficiency: 7-8%
• NASA’s needs: multiple times exceeding available stock

Sources of Plutonium-238 and Their Limitations

The main producers of plutonium-238 are the United States and Russia, but only one facility operates in Russia—the enterprise in Sarov, which started in 2000. While the U.S. resumed plutonium-238 production in 2013, it has yet to reach the required output level of 5 kg per year. According to NASA, the 2026 lunar mission will require at least 1.5 kg of this radioactive isotope, highlighting the severity of the current shortage.

Production Limitations

Despite efforts, production constraints remain a challenge. For instance, the high cost of building new reactors and upgrading existing technologies hinders expansion. In the U.S., establishing new plutonium-238 production facilities may cost hundreds of millions of dollars, making the process both technically and financially difficult.

• U.S. production capacity: 5 kg per year.
• Plutonium-238 needed for NASA mission: 1.5 kg.
• Cost to build new capacity: hundreds of millions of dollars.

The Role of RTGs in Space Missions

Radioisotope thermoelectric generators (RTGs) play a key role in meeting the energy demands of space missions. For example, the Cassini and New Horizons missions used 24 and 10 kg of plutonium-238, respectively. These devices provide stable power where solar panels are ineffective, such as at great distances from the Sun or in constant shadow. NASA data shows about 80% of all interplanetary missions rely on RTGs as their primary power source.

Future Missions and Plutonium-238 Demand

In 2026, a new mission to explore Titan is planned, requiring 2 kg of plutonium-238. This underscores the ongoing dependence of space agencies on this isotope to carry out ambitious projects. Given the growing shortage of plutonium-238 needed for RTGs, it is important to explore alternative energy sources and technologies for future space exploration.

• Cassini mission: 24 kg of plutonium-238
• New Horizons mission: 10 kg of plutonium-238
• Planned Titan mission: 2 kg of plutonium-238
• 80% of interplanetary missions use RTGs

Alternatives to RTGs and Their Efficiency

Given the plutonium-238 shortage for RTGs (radioisotope thermoelectric generators), alternative energy sources for space missions must be considered. Solar panels, for example, can generate up to 200 W per square meter, but their efficiency drops sharply at greater distances from the Sun. In Jupiter’s orbit or interstellar space, solar panels may provide only 10-20% of their maximum power, making them unsuitable for long-term missions to distant objects such as Triton or planets beyond the Solar System.

Nuclear Technologies as an Alternative

Nuclear reactors like the Kilopower project offer higher power output—up to 10 kW. However, their use requires complex cooling systems and they add significant weight. For example, the Kilopower reactor weighs about 200 kg, which can be critical for some missions. In contrast, RTGs are more compact: estimates suggest they are 3-5 times smaller in volume than solar panels needed at large distances from the Sun.

• Solar panels: up to 200 W/m², efficiency drops to 10-20% beyond 5 AU
• Kilopower project: up to 10 kW, weight 200 kg, cooling requirements
• RTGs: 3-5 times more compact than solar panels at distance from the Sun

Global Efforts to Address the Shortage

In 2026, the U.S. will allocate $15 million toward research and development of new methods for producing plutonium-238, a critically important component for powering space missions. These investments are part of a joint program between NASA and the U.S. Department of Energy (DOE) aimed at restoring production capacity by 2030. Within this initiative, by 2026 around 40% of plutonium-238 will be recovered from reprocessed spent nuclear fuel, significantly reducing dependence on primary sources of this radioactive isotope.

Current Initiatives and Goals

NASA and DOE’s joint efforts also include upgrading existing production facilities. In particular, plans to build a new plutonium-238 production plant aim to increase output to 1.5 kilograms per year by 2030. This will greatly improve the reliability and sustainability of supplies for future space missions.

• 2026 investments: $15 million
• Plutonium-238 from reprocessed fuel: 40% by 2026
• Planned production capacity: 1.5 kilograms per year by 2030

Frequently Asked Questions

Key Takeaways

• Plutonium-238 is a key element for RTGs.
• In 2026, the U.S. requires 1.5 kg of plutonium-238 for a lunar mission.
• The plutonium-238 shortage has reached a critical level—only 30 kg are available worldwide.