New small fission reactor for deep-space missions demonstrated


November 28, 2012

Artists concept of spacecraft using the Los Alamos reactor

Artists concept of spacecraft using the Los Alamos reactor

Image Gallery (8 images)

Exploring the regions of deep space beyond Mars means sending probes where solar power isn’t practical. Since the 1960s, NASA has equipped its Apollo missions and unmanned explorers with Radioisotope Thermal Generators (RTGs). These have worked very well, but they run on plutonium 238, which is currently in short supply. Therefore, the Los Alamos National Laboratory is developing a new small nuclear reactor for spacecraft that uses uranium instead of plutonium to power Stirling engines and generate electricity.

Los Alamos sees its reactor as a supplement to RTGs, allowing scarce plutonium to be held in reserve for missions where there’s no substitute. The finished product that will be installed in a spacecraft is a very simple design consisting of a 12-inch (30 cm) high and 4-inch (10 cm) wide hollow reactor core containing a cylinder of enriched uranium with a weight of 50 lbs (23 kg) and diameter of around 4 inches (10 cm).

This is surrounded by a Beryllium reflector with a mechanism at one end for removing and inserting a single rod of boron carbide, which starts and stops the reactor, respectively. The reflector catches escaping neutrons and bounces them back into the core, improving the efficiency of the reaction.

Side view of the Los Alamos reactor

Behind the reactor is a radiation shield, which protects the rest of the spacecraft from the core’s radiation. Heat pipes are used to transfer heat energy from the core to a number of Stirling engines – a closed-loop engine that runs on heat differences. This cools the reactor and powered the Stirling engines, which are used to run a dynamo to generate electricity.

At the Nevada National Security Site’s Device Assembly Facility near Las Vegas, engineers from Los Alamos, the NASA Glenn Research Center and National Security Technologies LLC conducted a Demonstration Using Flattop Fissions (DUFF) experiment that produced 24 watts of electricity using a pair of free-piston Stirling engines. The DUFF is a sort of "lab bench nuclear reactor," similar to experimental setups developed during the Second World War. This DUFF is the first demonstration of a space nuclear reactor to produce electricity in the United States since 1965.

Cutaway view of the Los Alamos reactor

“The nuclear characteristics and thermal power level of the experiment are remarkably similar to our space reactor flight concept,” said Los Alamos engineer David Poston. “The biggest difference between DUFF and a possible flight system is that the Stirling input temperature would need to be hotter to attain the required efficiency and power output needed for space missions.”

Though successful, the Stirling engine system used in the experiment isn't considered enough for practical purposes. For missions beyond Jupiter, much more power is needed. “The heat pipe and Stirling engine used in this test are meant to represent one module that could be used in a space system,” said Marc Gibson of NASA Glenn. “A flight system might use several modules to produce approximately one kilowatt of electricity.”

The Los Alamos video below explains the reactor's operation.

Source: Los Alamos National Laboratory

Update: This article was amended on Nov. 30, 2012, to clarify the functioning of the reactor.

About the Author
David Szondy David Szondy is a freelance writer based in Monroe, Washington. An award-winning playwright, he has contributed to Charged and iQ magazine and is the author of the website Tales of Future Past. All articles by David Szondy

I'd wonder if neutrino fired hydrogen peroxide would function similarly in deep space as it does miles underground.


Sound cool. Forget about space, I want one at home. But dont heat pipes require gravity to function?

Buck Smith

Ok never mind my comment about gravity. The wikipedia tells me one can make a heat pipe with capillary force in place of gravity. So clever.

Buck Smith

and we don't use sterling engines from whatever fuel source is what? if it is dependable enough to be in space where there is no mechanic then is sounds reliable enough for my backyard front-yard porch...


can apply to Manned Space IE ISS or Lunar base??

Stephen Russell

Sounds like a really good idea. (Kind of thinking somewhat out of the box.) Now you'll probably have some environmentalist raising a stink about "Nukes in Space".


Pretty amazing how it's able to dump waste heat space into near vacuum. I wonder how the thing is going to look like for a 1-kilo watt power generator

Fretting Freddy the Ferret pressing the Fret

@hogi90 For earth based engines there are more effective and efficient options. Mainly Stirling engines end up being lower power and torque for there size.

@Stephen Earth orbit and the moon are inside Mars orbit so Solar is a much better option. Also for manned operations the power budget would be much higher and need a larger more complex reactor. As an example the ISS solar arrays generate 84,000 Watts while the RTG on the Mars science Lab only generates 125 Watts.

Douglas Thomas

@hogi90 @Douglas Also, we do use Stirling engines for some things. Here's a common use, for example:

Wikipedia has a decent overview of some advantages and disadvantages of Stirling engines versus internal combustion engines:

Dwight Divine

The Feynman's lectures on physics level question is - In a capillary heat pump what energy source moves the lquid from cold side bacl to hot side?

Buck Smith

As I recall, the Soviet military used several nuclear reactors on military radar reconnaissance satellites back in the 1980's. They were supposed to use thermionic emission converters ( sort of a vacuum tube battery), with an efficiency of 50% or so. The US (NASA, I think) actually bought one of the converters. I'm sure we are talking tens of kilowatts. I would be interested in knowing why Stirling engines were chosen. Perhaps much smaller size & mass, less power needed?

Al S.

please donate some to poor countries who have no/expensive electricity

Vincent Maldia

re; Douglas Thomas

Night lasts two weeks on the moon. Unless you are on a pole solar is not viable.


re; Al S.

The thermocouples that convert the heat to electricity on the Voyager spacecraft are decaying due to radiation exposure at a rate that doubles the power loss from the nuclear power pack. With magnetic or other long life bearings Stirling engines should last longer.


The rocket launch in the video is a SpaceX Falcon 1 !! 3:30 Veddy interestin' .

Brian Hall
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