NASA has received permission to use RTG with plutonium-238 in another mission

Plutonium-238 in the iridium granule glows red and for decades produces a large amount of heat. Such granules are installed in radioisotope thermoelectric generators (RTGs) that generate electricity.

The director of NASA's Department of Planetology, James Green, sent out a memo on radioisotope heat generators (RTGs).

“After analyzing and consulting with the Ministry of Energy, the NASA Department of Planetology is pleased to announce applicants who intend to participate in the upcoming Discovery program to lift the ban on the use of radioisotope energy sources (Radio-isotope Power Systems, RPS),” said a memo.
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After obtaining permission, applicants can include up to two radioisotope heat generators in their bids, and thus significantly expand the concept of Discovery missions.

Discovery is a program for low-cost, highly specialized space missions for the scientific study of the solar system. “Low budget” compared to the missions of the New Frontiers or Flagship programs, of course. In absolute terms, their budget is quite decent. As part of the Discovery program, missions were prepared by NEAR Shoemaker (the very first mission to study the asteroid 433 Eros in 1996), Mars Pathfinder (the descent vehicle that brought the Sojourner planetary rover to Mars), Stardust, Deep Impact, Dawn, Kepler and many others.

Back in December, the “long-term planning information” for the Discovery program reported that installing radioisotope sources of energy RPS is prohibited. Only radioisotope heaters (RHU) with a very small amount of plutonium-238 were allowed to heat up scientific instruments and other elements of the spacecraft. Now the restriction has been removed.

The full-scale use of plutonium-238 was made possible by estimating projected reserves of this fuel at the rate of consumption in future missions, such as Mars 2020, Space News reported . Dragonfly, one of the two finalists of the planetary scientific mission of the middle class in the New Frontiers program, and future vehicles who have to work on the lunar surface during a two-week lunar night, when the ground freezes to -170 ° C, claim their share of rare material.

Plutonium-238 is still in a very large deficit. Only about 2022, the Ministry of Energy will reach the production volume of about 1.5 kg per year, and until that time it is necessary to strictly limit the consumption of the isotope. James Greene’s harsh economy explained why the mission was initially forbidden to use radioisotope energy sources: “The last thing we would like to encounter is to choose a mission, and then not be ready for flight.”

After the publication of “long-term planning information,” Green returned to the Department of Energy again to recalculate current and projected plutonium-238 stocks. Such perseverance brought success: in the end, the numbers came together as needed - and it turned out that there really was enough fuel for another mission.

A more optimistic plutonium stock forecast came from the progress the US Department of Energy made in extracting this valuable isotope. Apparently, American nuclear physicists will be able to reach a volume of 1.5 kilograms per year as scheduled.

Production of plutonium-238 in the United States was halted in the late 1980s, and now production is recovering at a slow pace. Since 1992, plutonium-238 was purchased from Russia, but in 2009 the deal fell through, which put the United States in a difficult position . At the beginning of 2015, 35 kg of plutonium remained in the reserves, of which only 17 kg correspond to the required quality for creating spacecraft power sources, which roughly corresponds to the three atomic elements installed in the Curiosity rover.

The Oak Ridge National Laboratory has developed plutonium-238, the first in the last 30 years, by December 2015, and now the United States is gradually recovering the isotope, which is so necessary for space missions. Plutonium-238 is obtained from neptunium-237, which is extracted from the fuel of nuclear reactors.

But because of such trifles, the US could lose its global leadership in space research, because without plutonium-238 in deep space, there is nothing to do: “It would not be a great exaggeration to say that the future of undisputed US leadership in the field of planetary research in the 21st century depends on plutonium -238, said Alan Stern, head of the New Horizon mission, in an interview with Space.com online newspaper. “We can still undertake one research mission after Curiosity, but that’s all.” Some kind of madness. It is irresponsible to approach so close to the edge of the abyss. We need to turn to the Russians, to get to the orbital station, we can no longer explore the moon as in the times when I was a boy, and now also lose the ability to explore the solar system to its very limits. ”

But now the situation is close to a successful resolution. The Department of Energy managed to scale up production - and NASA should soon receive plutonium-238 in the required amount.