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JOSH: It takes a lot of power
to run a space program.

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And in some places where NASA
will go in the future, they

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don’t have access to anything
like this.

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So agency scientists and
engineers are looking to do

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some huge things... on a very
small scale.

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NASA goes nuclear, next on Real
World.

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? [music] ?

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JOSH: NASA’s mission to explore
worlds beyond our own would

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never get off the ground
without innovative ways to

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power all the operations that
make that possible.

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MIKE HOUTS: To explore the
universe, you need

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lots of energy...
JOSH: Mike Houts is a nuclear

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research manager at Marshall
Space Flight Center.

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MIKE: One of the areas that
NASA is looking at right now is

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fission. And so this is
actually using the nuclear

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fission process to generate
energy that can be

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used for any of our exploration
needs.

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JOSH: Atoms are the most basic
units of matter.

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The nucleus of an atom contains
positively charged particles

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called protons. The number of
protons in an atom determines

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the atomic number of an
element. Elements are arranged

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on the periodic table according
to their atomic number

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Atoms of the same element have
the same number of protons and

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electrons, but might have
different number of neutrons.

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Atoms with different numbers of
neutrons are called isotopes.

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Some elements have isotopes
that are unstable... that is,

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they do not hold together well.
When they break apart, they

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undergo a nuclear reaction and
become radioactive. Two new

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elements are produced. The
atomic number of these two

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elements adds up to the atomic
number of the original element.

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Here’s an example. Start with
an atom of Uranium.

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Its atomic number is 92. When
this atom splits, through

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nuclear fission, you get two
new elements.

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One might be say, Barium with
an atomic number of 56.

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So what would the other one be?
Do the math.

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Subtract the atomic number of
barium, 56 from the atomic

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number of Uranium, 92.

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You’re left with 36.

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And that is the atomic number
of krypton, the other element.

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When uranium splits, many
elements can result, but the

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atomic number of the new
elements will always be between

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32 and 60 and the sum of their
atomic numbers will always be

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92, the atomic number of
uranium.

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Okay, back to Mike Hauts.
He and his team are working to

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develop a viable energy source
that would satisfy

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many needs of space
exploration.

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MIKE: The applications...
Everything from life support

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systems, to in-situ resource
utilization, some

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communications, really just all
of the outpost activities is

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what they’re looking at using
the electricity for.

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JOSH: The system is based on
old technology, the Stirling

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Engine, which was originally
developed in the 19th century.

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The engine converts heat into
electricity.

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So nuclear fission would create
the heat that the sterling

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engine would turn into useable
electricity to power

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operations. This system is
designed for about 40 kilowatts

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of power. That would power
about 8 houses here on earth.

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That’s a little more than a
solar array on the space

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station, which can produce 32
kilowatts.

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Plus with the nuclear power
plant, you don’t need sunlight.

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MIKE: It’s a very high power by
NASA standards.

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It really gives us the
opportunity to have a power

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rich environment. It can also
be operated anywhere on the

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surface of the moon, anywhere
on the surface of Mars. So it

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gives us a lot of flexibility,
a lot of power capability,

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but as reactors go, it’s
actually very, very tiny.

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Compared to a terrestrial
reactor,

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it’s about 1/20,000th the power
level.

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JOSH: And the safety concerns
associated with nuclear power

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are virtually non-existent with
this system.

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MIKE: They have what‘s called a
negative temperature reactivity

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feedback coefficient. What that
basically means is if the

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reactor starts to warm up, the
system itself actually gets

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less reactive, and that’ll tend
to cool the system down.

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The system starts to cool down
too much, they system will

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actually shrink and become
slightly more reactive.

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That’ll cause it to heat back
up. So the systems

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themselves are very stable.
JOSH: And any fears about the

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nuclear material creating a
disaster in the event of a

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launch mishap would be erased
thanks to good engineering.

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MIKE: The nice point about
reactors is they operate

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basically by having the right
materials get in the right

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geometry, and that will cause
the reactor to turn on.

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And so what’s been done in this
system is to basically make

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sure it only turns on when you
want it to turn on. And the

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system is designed such that
during launch, any credible

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launch accident, that it will
not inadvertently turn on.

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JOSH: So very safe... and
incredibly efficient...

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MIKE: The amount of fuel we
have on board, we burn about 1

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percent of our fuel every 12
years. And so we’re not going

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to run out of fuel, however
there will be other parts of

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the system that might limit the
lifetime.

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JOSH: The prototype system
doesn’t use nuclear fission.

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That’s for a future iteration
of the concept. For now, it

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uses resistance heaters that
closely mimic

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the heat from fission. The
Sterling engine turns

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that heat into electricity.
Here’s how it works...

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MIKE: What that simulator does
is it heats the coolant and in

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this case we’re using a coolant
that is a mixture of sodium and

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potassium, heats that coolant
to about 850 Kelvin.

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And then that hot coolant is
used to provide power to the

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sterling power conversion
subsystem. And what that does

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is it takes a portion of the
energy that’s in the NaK

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Coolant and converts it into
electricity.

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About 25 percent of that energy
is converted from heat to

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electricity. Now in the process
of that energy being

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transferred to the sterling
engine, it actually cools the

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NaK down. And so that slightly
cooler NaK, then goes though

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the circuit, it’s
re-pressurized in a pump and

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back through the core
stimulator, where it’s heated

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goes back up and then
continues in the circuit.

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JOSH: NASA scientists, working
with the Department of Energy

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think that they could have a
nuclear fission based version

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of this system in place within
5 to 6 years

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Keep track of this project and
all of NASA’s missions,

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at www.nasa.gov.

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