The shipment earlier this year of heat source plutonium-238 from the US Department of Energy’s (DOE’s) Oak Ridge National Laboratory (ORNL) to its Los Alamos National Laboratory (LANL) represents a critical step toward fuelling planned space missions with radioisotope power systems, NASA had said.

The shipment of 0.5 kilograms of new heat source plutonium oxide is the largest since the domestic restart of plutonium-238 production more than 10 years ago. “It marks a significant milestone toward achieving the constant rate production average target of 1.5 kilograms per year by 2026,” NASA noted.

Radioisotope power systems (RPS) use the natural decay of the radioisotope plutonium-238 to provide heat to a spacecraft in the form of a Light Weight Radioisotope Heater Unit (LWRHU), or heat and electricity in the form of a system such as the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG). RPS will enable exploration of some of the deepest, darkest, and most distant destinations in the solar system and beyond.

DOE has produced the heat source plutonium oxide required to fuel the RPS for missions such as NASA’s Mars 2020. The first spacecraft to benefit from this restart, the Perseverance rover, carries some of the new plutonium produced by DOE. An MMRTG continuously provides the car-sized rover with heat and about 110 watts of electricity, enabling the exploration of the Martian surface and the gathering of soil samples for possible retrieval.

“NASA’s Radioisotope Power Systems Program works in partnership with the Department of Energy to enable missions to operate in some of the most extreme environments in our solar system and interstellar space,” said Carl Sandifer, RPS programme manager at NASA’s Glenn Research Center in Cleveland.

For more than 60 years, the US has employed radioisotope-based electrical power systems and heater units in space. Three dozen missions have explored space for decades using the reliable electricity and heat provided by RPS. NASA and DOE are continuing their long-standing partnership to ensure the US can enable future missions requiring radioisotopes for decades to come.

Earlier, plutonium-238 was supplied to the US directly from Russia. At a cost of some $2.5m per kilogram. However, this trade ended due to the restructuring of the Russian nuclear industry. Nevertheless, the stockpiled Russian plutonium-238 was enough to equip most American spacecraft for some time. DOE in 2013 set a target of starting production of its own product in quantities of at least 1.5 kg a year. ORNL in 2015 produced the first US-produced Pu-238 in nearly three decades. It was shipped to LANL for fabrication.

Image: The Perseverance rover was the first to benefit from the new plutonium produced by the USDOE (courtesy of NASA)