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.

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

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

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

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