A planned U.S. mission to investigate three ice-covered moons of Jupiter will demand fast-paced research, fabrication and realistic non-nuclear testing of a prototype nuclear reactor within two years, says a Los Alamos National Laboratory scientist.

An artist's concept of Jupiter Icy Moons Orbiter. Credit: NASA/JPL

The roots of this build and test effort have been under way at Los Alamos since the mid-1990s, said David Poston, leader of the Space Fission Power Team in Los Alamos' Nuclear Design and Risk Analysis Group.

NASA proposes using use electrical ion propulsion powered by a nuclear reactor for its Jupiter Icy Moons Orbiter, an element of Project Prometheus, which is scheduled for launch after 2011. However, the United States hasn't flown a space fission system since 1965.

Poston discussed technical requirements for such a fission reactor in two presentations Monday at the Space Technology and Applications International Forum in Albuquerque. Los Alamos is a co-sponsor of the forum. Poston discussed "The Impact of Core Cooling Technology Options on JIMO Reactor Designs" and "The Impact of Power and Lifetime Requirements on JIMO Reactor Designs."

Los Alamos is leading reactor design for the Jupiter Icy Moons Orbiter mission, which would orbit Callisto, Ganymede and Europa to study their makeup, possible vast oceans beneath the ice, their history and potential for sustaining life. Los Alamos is responsible for such key reactor technologies as nuclear fuel, beryllium components, heat pipes and diagnostic instruments, as well as nuclear criticality testing of development and flight reactors.

"Nuclear power has long been recognized as an enabling technology for exploring and expanding into space, and fission reactors offer essentially limitless power and propulsion capabilities," Poston said.

The JIMO mission demands a safe, low-mass, high-temperature reactor that can be developed and qualified quickly, can operate reliably in the harsh environment of space for more than a decade, and can meet a wide range of mission and spacecraft requirements, he said.

A science mission to explore the icy Jovian moons will require kilowatts of electrical power for the scientific payloads and up to 100 kilowatts of electricity for ion propulsion to propel the spacecraft to Jupiter, maneuver within the Jovian system and allow rendezvous with the moons. The reactor also must power advanced science experiments and systems to send data to Earth at high rates.

Despite the lack of U.S. space reactor research in recent decades, Los Alamos has continued to examine technologies and concepts for a rapid and affordable development program. Working with NASA's Marshall Space Flight Center, Los Alamos has resolved many hardware issues at the component and system level.

Los Alamos and NASA-Marshall researchers, working with colleagues from NASA's Jet Propulsion Laboratory and Sandia National Laboratories, have built successively more powerful nuclear electric propulsion reactor components, including a 30-kilowatt reactor core, one-third of a 100-kilowatt system (core plus heat exchanger) and a single module suitable for a 500-kilowatt reactor core. Extensive non-nuclear testing of these and other components continues.

Most researchers have agreed on the best fuels and reactor construction materials for the proposed fast-spectrum, externally controlled JIMO reactor. The major design choice that remains is how best to transport power from the reactor core to the power conversion system.

Los Alamos and NASA are examining three primary options for core cooling: pumped liquid-metal sodium or lithium; sodium or lithium liquid metal heat pipes; and inert helium or helium-xenon gas. Many of these options have been tested for decades for terrestrial reactors, but the reactor for JIMO will be unique, Poston said.

"The power and lifetime potential of space fission reactors is almost limitless when compared to the requirements of future NASA missions," Poston said. "However, it is clear that reactor performance and technical risks are tightly coupled to power and lifetime requirements, so we must thoroughly understand these technical risks before developing the first system. For example, there are fewer technical and development challenges for a 500-kilowatt-thermal reactor than a 1,000-kilowatt-thermal reactor.

"The first step needs to be small enough to ensure success and to put into place the experience, expertise and infrastructure necessary for more advanced systems," Poston concluded. "After that, we can move on to the systems needed for truly ambitious space exploration, such as multi-megawatt nuclear electric propulsion or nuclear thermal rockets. Our near-term efforts must be focused on making the first mission succeed."

Los Alamos National Laboratory is operated by the University of California for the National Nuclear Security Administration (NNSA) of the U.S. Department of Energy and works in partnership with NNSA's Sandia and Lawrence Livermore national laboratories to support NNSA in its mission.

Los Alamos develops and applies science and technology to ensure the safety and reliability of the U.S. nuclear deterrent; reduce the threat of weapons of mass destruction, proliferation and terrorism; and solve national problems in defense, energy, environment and infrastructure.