The Energy Collective Group

This group brings together the best thinkers on energy and climate. Join us for smart, insightful posts and conversations about where the energy industry is and where it is going.

9,750 Subscribers

Article Post

NASA Space Missions to Get a Boost from Nuclear Energy

  • The Space agency just completed a series of successful demonstration tests of the Kilopower nuclear power system that will be an essential part of future missions to the Moon and Mars.
  • NASA authorizes the use of PU-238 as a power source in future multi-mission radioisotope thermoelectric generators, or MMRTGs, for deep space science missions throughout this decade.

KiloPower Tests Successful


KiloPower Design – Image: NASA

NASA and the Department of Energy’s National Nuclear Security Administration (NNSA) have successfully demonstrated KiloPower, which is a new nuclear reactor power system that could enable long-duration crewed missions to the Moon, Mars and destinations beyond.

NASA announced the results of the demonstration, called the Kilopower Reactor Using Stirling Technology (KRUSTY) experiment, during a news conference this week at the NASA Glenn Research Center in Cleveland.

The Kilopower experiment was conducted at the NNSA’s Nevada National Security Site from November 2017 through March 2018.

NASA officials said they expect the Kilopower project to be an essential part of lunar and Mars power architectures as they evolve.

Kilopower is a small, lightweight fission power that uses passive liquid sodium for heat transfer to stirling engines which produce electrical power. The system as tested is capable of providing up to 10 kilowatts of electrical power – enough to run several average households – continuously for at least 10 years. Four Kilopower units would provide enough power to establish an outpost on the moon or Mars.

According to Marc Gibson, lead Kilopower engineer at NASA Glenn, the pioneering power system is ideal for the Moon where power generation from sunlight is difficult because lunar nights are equivalent to 14 days on Earth.

“Kilopower gives us the ability to do much higher power missions, and to explore the shadowed craters of the Moon,” said Gibson.

“When we start sending astronauts for long stays on the Moon and to other planets, that’s going to require a new class of power that we’ve never needed before.”

The prototype power system uses a solid, cast uranium powered reactor core. Passive sodium heat pipes transfer reactor heat to high-efficiency Stirling engines, which convert the heat to electricity.

NNSA Hosts Test Sessions at Nevada

According to David Poston, the chief reactor designer at NNSA’s Los Alamos National Laboratory, the purpose of the recent experiment in Nevada was two-fold: to demonstrate that the system can create electricity with fission power, and to show the system is stable and safe no matter what environment it encounters.

The team took the design through a full power 20 hour test. The objective is to work towards certification of the power system for space flight.

“We threw everything we could at this reactor, in terms of nominal and off-normal operating scenarios and KRUSTY passed with flying colors,” said Poston.

The Kilopower team conducted the experiment in four phases.

  • The first two phases, conducted without power, confirmed that each component of the system behaved as expected.
  • During the third phase, the team increased power to heat the core incrementally before moving on to the final phase.
  • The experiment culminated with a 28-hour, full-power test that simulated a mission, including reactor startup, ramp to full power, steady operation and shutdown.

Throughout the experiment, the team simulated power reduction, failed engines and failed heat pipes, showing that the system could continue to operate and successfully handle multiple failures.

“We put the system through its paces,” said Gibson. “We understand the reactor very well, and this test proved that the system works the way we designed it to work. No matter what environment we expose it to, the reactor performs very well.”

Flight Qualification is the Goal

The Kilopower project is developing mission concepts and performing additional risk reduction activities to prepare for a possible future flight demonstration.  NASA said that the next 18 months of work will determine whether the KiloPower design can meet the rigors of space flight. These challenges include the launch phase and exposure to the deep cold of outer space

Such a demonstration could pave the way for future Kilopower systems that power human outposts on the Moon and Mars, including missions that rely on In-situ Resource Utilization to produce local propellants, water, oxygen, and other materials.

The Kilopower project is led by NASA Glenn, in partnership with NASA’s Marshall Space Flight Center in Huntsville, Alabama,and NNSA, including its Los Alamos National Laboratory, Nevada National Security Site and Y-12 National Security Complex.

KiloPower Resources Online

FactsheetVideoNASA KiloPower home pageBriefing – Nuclear Power in Space

NASA to Use Nuclear Fission Power Systems for Next Discovery Mission

nasa logoSpaceNews: Citing progress in producing plutonium-238, NASA will allow scientists proposing missions for upcoming planetary science missions to use nuclear power sources for electricity to run scientific instruments.

In a statement issued March 17, Jim Green, director of NASA’s planetary science division, said the agency has reversed an earlier decision prohibiting the use of radioisotope power systems for spacecraft proposed for the next mission in the agency’s Discovery program.

NASA made that decision based on projected use of existing stocks of plutonium-238 for upcoming missions, such as the Mars 2020 rover.

Dragonfly, one of the two finalists for the next New Frontiers medium-class planetary science mission, also plans to use a PU-238 radioisotope power system, as well as potential future missions the moon that require nuclear power to operate through the two-week lunar night.

Still, the agency needed to balance mission demands against existing inventory of plutonium and new efforts currently to produce new supplies of the isotope, which should reach a goal of 1.5 kilograms a year by around 2022.


Planning for the next Discovery mission is still in its earliest stages. NASA plans to release a draft announcement of opportunity in September 2018 for comment, followed by the final announcement in February 2019. NASA will select finalists for further study in December 2019, with a winner chosen in June 2021 for launch no later than the end of 2026.

The key to successful deep space science missions, beyond the orbit of Mars, is to have enough electrical power to sustain the entire mission over many years powering the science instruments and the transmission of massive amounts of data back to earth.  There is not enough sunlight beyond Mars orbit to meet these needs hence the need for nuclear fission powered electrical systems.

Original Post

Content Discussion

Matt Chester's picture
Matt Chester on May 9, 2018

Thanks for the write-up Dan.

How do these nuclear systems differ from the ones conventionally used for power generation here on earth? Are they less efficient because of the adjustments needed to get them to work in space, or is there a chance this is also a technology that could change nuclear power plants today?

David Hervol's picture
David Hervol on May 10, 2018

These reactors use small, fast neutron reactors with HEU as fuel. So it’s not applicable to terrestrial applications. The Stirling convertor is not scalable to high power levels. For large power levels using specific power as a metric, Brayton convertors make more sense. This occurs around 100 kW (or less if higher cycle temperatures are used). These are definitely a great deal better than RTG’S using Pu 238 since the reactor is launched cold and only activated at very high orbits with a very long decay orbit of thousands of years similar to SNAP10A. These power systems are needed if we are to explore with any realistic onboard power much beyond the orbit of Mars.

Engineer- Poet's picture
Engineer- Poet on May 10, 2018

There are such radical differences in both scale and operating conditions (specifically, heat sink temperature) that the Stirling technology really doesn’t translate to dirt-side power plants.  It’s one thing when you’ve got a body of water at no more than about 300 K to put heat into; it’s a very different thing when you have to get up to 400-500 K or more to be able to get rid of the heat with a radiator you can afford to carry on a spacecraft.

David Hervol's picture
David Hervol on May 11, 2018

EngineerPoet, good point. Matt, the small value of the Stefan-Boltzmann constant drives the delta T and real estate requirement to be quite large. The heat rejection radiator becomes the largest piece of hardware on conceptual nuclear-powered spacecraft. The exception is nuclear thermal where you are sending heated hydrogen out a nozzle for propulsion. Cooling towers or bodies of water are nice heat sinks.

Dan Yurman's picture
Dan Yurman on May 11, 2018

You asked in a comment at the Energy Collective if the NASA nuclear power unit could be used for applications on earth. The short answer is no. Reasons include;

** The nature of the nuclear fuel – highly enriched uranium which has dual uses, e.g., can be used to make weapons.
** Exotic and specialized nature of the coolant, liquid sodium heated by the reactor core. Sodium in any pure form is difficult to work with and in heated liquid form requires specialized engineering expertise and equipment.
** Only a few of these units will ever be built as more compact designs are likely to follow. Costs will remain high and out of reach for commercial use.

Hope this helps. Please contact me if you have other questions.