Plutonium-238 pellet
Plutonium-238 pellet. Credit: U.S. Department of Energy

SAN FRANCISCO — Despite repeated actions by U.S. lawmakers to deny funding for domestic production of plutonium-238 (Pu-238) in U.S. Energy Department budget bills, NASA has begun mapping out the steps needed to resume production of the nuclear material with money included in the space agency’s 2011 budget.

The most recent setback for efforts to restart Pu-238 came Sept. 7 when the U.S. Senate Appropriations Committee followed the example set by U.S. House of Representatives appropriators in June and approved a 2012 spending plan without any money for the program in the Energy Department’s budget. The administration of President Barack Obama asked for $20 million for the Pu-238 program in 2012, split evenly between NASA and the Energy Department. Lawmakers also denied funding for the program in the Energy Department’s 2010 and 2011 budgets.

NASA officials did receive congressional approval last spring to use money in the space agency’s 2011 budget to begin working with the Energy Department to study resumption of Pu-238 production. Lawmakers authorized NASA to begin looking into the issue in 2011. That effort was delayed, however, because Congress failed to pass a 2011 budget bill and instead provided the space agency with money through a series of stopgap spending measures designed to support ongoing activities. To spend money on new programs, including Pu-238 production, NASA officials needed congressional permission.

When that permission came in July, NASA transferred money to the Energy Department to begin studying “how as a nation we are going to do this,” said Jim Adams, NASA’s deputy director for planetary science. Adams declined to say precisely how much money the space agency gave the Energy Department for the Pu-238 study but said NASA was authorized to spend as much as $7.5 million on the effort. Because the year was well under way before the authority to spend that money was received, that entire $7.5 million was not needed for the current year, he added.

Space agency officials hope to augment that 2011 funding with $10 million the Obama administration is requesting in NASA’s 2012 budget for the Pu-238 program. That funding would enable the Energy Department to complete efforts in 2012 to determine the precise steps needed to resume Pu-238 production. “We would know categorically what it would cost and how long it would take,” Adams said.

In the 1980s, the Energy Department halted production of Pu-238, which provides electrical power for NASA missions including the Cassini mission to Saturn and the Mars Science Laboratory scheduled to launch in November. That supply has been nearly exhausted, according to a 2009 National Research Council (NRC) report.

If NASA cannot resume production of Pu-238, “it would not mean an end to deep-space exploration or an end to lunar geophysical stations, but the systems we could fly would be far less capable,” Alan Stern, former NASA associate administrator for science, said. “The missions would be a shadow of the exploration we can do today. You could not fly another Cassini, not by a long shot, and that would be tragic.”

Ralph McNutt, a planetary scientist who co-chaired an NRC panel that examined the Pu-238 issue, said U.S. production of Pu-238 should resume quickly because the country is losing the people who understand the complex processes involved in creating the isotope. “All the people who know how to do this are retiring or dead,” McNutt said.

Every mission NASA sends beyond Jupiter and most missions near Jupiter require an electric power generator because the sun is too dim at those distances to provide an abundant source of energy. One exception is NASA’s Juno mission to Jupiter launched in August, which was designed specifically to fly on solar power. The only other viable energy source is fuel cells, which can provide power for months, not nearly long enough for a five-year trip to Jupiter or a seven-year voyage to Pluto, Adams said. “We need a long-lived power supply because we go places where the sun is too dim or to planetary surfaces where the sun is not shining,” Adams said. Plutonium-filled radioisotope systems can power a spacecraft for decades.

Until 2008, U.S. officials supplemented their dwindling supplies of Pu-238 with periodic purchases from Russia. In 2009, however, Russia’s Rosatom State Atomic Energy Corp. reneged on a commitment to supply the Energy Department with the nuclear material in 2010 and 2011 and asked to negotiate a new agreement. “Pu-238 is so critical to planetary science, I don’t want to be dependent on an international agreement,” Adams said.

Even if NASA and the Energy Department are able to complete the current Pu-238 study and win approval to resume production, it is likely to take six to eight years before the new material is available for scientific missions. Once that production resumes, the Energy Department could provide an ongoing source of the material for planetary missions, Adams said.

NASA and the Energy Department are seeking to reduce future demand for Pu-238 by developing a new power source for space missions, the Advanced Stirling Radioisotope Generator (ASRG). The ASRG is four times more efficient than the Radioisotope Thermoelectric Generator currently used. While ASRGs hold great promise, they are still under development and space agency officials cannot be sure they will work until they are tested in spaceflight, McNutt said.

That testing may come in 2016. In May, NASA selected three finalists for the next Discovery mission, a robotic planetary expedition with a maximum cost of $425 million. Two of the missions, a probe that would land on a comet and another destined for Saturn’s moon Titan, would be powered by ASRGs.

“Over the course of 2012, we will come to some resolution on the issue of co-funding the project with the Energy Department,” Adams said. “If the Energy Department manages to convince appropriators that the department should share in funding this project, then we will have one path forward.” If not, NASA officials will find another way to pay for Pu-238 production, he added.

“We were fighting this battle four or five years ago, and it looks like we will be fighting it longer,” Adams said.

Debra Werner is a correspondent for SpaceNews based in San Francisco. Debra earned a bachelor’s degree in communications from the University of California, Berkeley, and a master’s degree in Journalism from Northwestern University. She...