The first U.S. production in nearly 30 years of a specialized fuel to power future deep space missions has been completed by researchers at the Department of Energy’s Oak Ridge National Laboratory (ORNL) in Tennessee.
The production of 50 grams of plutonium-238 -roughly the mass of a golf ball — marks the first demonstration in the United States since the Savannah River Plant in South Carolina ceased production in the late 1980s.
Radioisotope power systems convert heat from the natural radioactive decay of the isotope plutonium-238 into electricity. These systems have been used to power the exploration of the solar system and beyond, from the Viking missions on Mars, to the Voyager spacecraft entering interplanetary space, and most recently powering the Curiosity Mars Rover and the New Horizons spacecraft sailing past Pluto.
“This significant achievement by our team mates at DOE signals a new renaissance in the exploration of our solar system,” said John Grunsfeld, associate administrator for NASA’s Science Mission Directorate in Washington. “Radioisotope power systems are a key tool to power the next generation of planetary orbiters, landers and rovers in our quest to unravel the mysteries of the universe.”
The success of the engineers and technicians at ORNL comes two years after the project formally started with NASA funding, building on many years of research and testing. This demonstration of the key steps in fuel production will ensure that this vital space power technology will be available to provide electricity and heat for ambitious exploration missions of the solar system in this decade and beyond. In all, 27 past U.S. space missions have used this radioisotope power for their electricity and heat.
The Department of Energy (DOE) has successfully and safely provided radioisotope power systems for NASA, Navy and Air Force missions for more than 50 years.
“As we seek to expand our knowledge of the universe, the Department of Energy will help ensure that our spacecraft have the power supply necessary to go farther than ever before,” said Franklin Orr, Under Secretary for Science and Energy at DOE. “We’re proud to work with NASA in this endeavor, and we look forward to our continued partnership.”
The currently available radioisotope power system, also supplied to NASA by the DOE, is called the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG). Essentially a nuclear battery, an MMRTG can provide about 110 watts of electrical power to a spacecraft and its science instruments at the beginning of a mission. On some missions, such as NASA’s Curiosity Mars rover (now deep into its third Earth year seeking signs of habitable conditions on the Red Planet), the excess heat from the MMRTG can also be used to keep spacecraft systems warm in cold environments.
The next NASA mission planning to use an MMRTG is the Mars 2020 rover, due to be launched as part of NASA’s Journey to Mars, to seek signs of past life on the Red Planet, test technology for human exploration, and gather samples of rocks and soil that could be returned to Earth in the future. Two (unfueled) MMRTGs are currently built and in storage at DOE facilities; one is reserved for Mars 2020, and the other could be used on a future mission. Fabrication of the fuel pellets for the Mars 2020 MMRTG, using the existing U.S. supply of plutonium dioxide, is already underway.
Researchers will analyze the sample for chemical purity and plutonium-238 content to determine whether adjustments need to be made before scaling up the process.
With continued coordination, both agencies plan to increase production after this important demonstration milestone and will start with about 12 ounces (300 to 400 grams) of plutonium dioxide per year. After implementing greater automation and scaling up the process, ORNL will produce an average of 3.3 pounds (1.5 kilograms) in subsequent years.
Of the 77 pounds (35 kilograms) of existing plutonium-238, about half provide enough heat to meet power specifications of planned spacecraft. The remainder, due to its age, does not meet specifications, but can be blended with newly produced Pu-238 to extend the usable inventory.
The DOE’s Office of Nuclear Energy develops, manufactures, tests and delivers radioisotope power systems for space exploration and national security missions and maintains responsibility for nuclear safety throughout all aspects of the missions.
NASA’s Radioisotope Power System (RPS) program, managed by NASA Glenn Research Center in Cleveland, is funding the development of new, higher efficiency thermoelectric materials that could be incorporated into a next-generation enhanced MMRTG that would provide about 25 percent more power at the start of a typical mission, and 50 percent more power at the end of a mission.
NASA’s Jet Propulsion Laboratory, Pasadena, California, is part of the RPS program and manages several missions that utilize radioisotope power, including the Curiosity Mars rover and the Cassini spacecraft at Saturn.