JOSH: It takes a lot of power to run a space program.
And in some places where NASA will go in the future, they
don't have access to anything like this.
So agency scientists and engineers are looking to do
some huge things... on a very small scale.
NASA goes nuclear, next on Real World.
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JOSH: NASA's mission to explore worlds beyond our own would
never get off the ground without innovative ways to
power all the operations that make that possible.
MIKE HOUTS: To explore the universe, you need
lots of energy... JOSH: Mike Houts is a nuclear
research manager at Marshall Space Flight Center.
MIKE: One of the areas that NASA is looking at right now is
fission. And so this is actually using the nuclear
fission process to generate energy that can be
used for any of our exploration needs.
JOSH: Atoms are the most basic units of matter.
The nucleus of an atom contains positively charged particles
called protons. The number of protons in an atom determines
the atomic number of an element. Elements are arranged
on the periodic table according to their atomic number
Atoms of the same element have the same number of protons and
electrons, but might have different number of neutrons.
Atoms with different numbers of neutrons are called isotopes.
Some elements have isotopes that are unstable... that is,
they do not hold together well. When they break apart, they
undergo a nuclear reaction and become radioactive. Two new
elements are produced. The atomic number of these two
elements adds up to the atomic number of the original element.
Here's an example. Start with an atom of Uranium.
Its atomic number is 92. When this atom splits, through
nuclear fission, you get two new elements.
One might be say, Barium with an atomic number of 56.
So what would the other one be? Do the math.
Subtract the atomic number of barium, 56 from the atomic
number of Uranium, 92.
You're left with 36.
And that is the atomic number of krypton, the other element.
When uranium splits, many elements can result, but the
atomic number of the new elements will always be between
32 and 60 and the sum of their atomic numbers will always be
92, the atomic number of uranium.
Okay, back to Mike Hauts. He and his team are working to
develop a viable energy source that would satisfy
many needs of space exploration.
MIKE: The applications... Everything from life support
systems, to in-situ resource utilization, some
communications, really just all of the outpost activities is
what they're looking at using the electricity for.
JOSH: The system is based on old technology, the Stirling
Engine, which was originally developed in the 19th century.
The engine converts heat into electricity.
So nuclear fission would create the heat that the sterling
engine would turn into useable electricity to power
operations. This system is designed for about 40 kilowatts
of power. That would power about 8 houses here on earth.
That's a little more than a solar array on the space
station, which can produce 32 kilowatts.
Plus with the nuclear power plant, you don't need sunlight.
MIKE: It's a very high power by NASA standards.
It really gives us the opportunity to have a power
rich environment. It can also be operated anywhere on the
surface of the moon, anywhere on the surface of Mars. So it
gives us a lot of flexibility, a lot of power capability,
but as reactors go, it's actually very, very tiny.
Compared to a terrestrial reactor,
it's about 1/20,000th the power level.
JOSH: And the safety concerns associated with nuclear power
are virtually non-existent with this system.
MIKE: They have whatĎs called a negative temperature reactivity
feedback coefficient. What that basically means is if the
reactor starts to warm up, the system itself actually gets
less reactive, and that'll tend to cool the system down.
The system starts to cool down too much, they system will
actually shrink and become slightly more reactive.
That'll cause it to heat back up. So the systems
themselves are very stable. JOSH: And any fears about the
nuclear material creating a disaster in the event of a
launch mishap would be erased thanks to good engineering.
MIKE: The nice point about reactors is they operate
basically by having the right materials get in the right
geometry, and that will cause the reactor to turn on.
And so what's been done in this system is to basically make
sure it only turns on when you want it to turn on. And the
system is designed such that during launch, any credible
launch accident, that it will not inadvertently turn on.
JOSH: So very safe... and incredibly efficient...
MIKE: The amount of fuel we have on board, we burn about 1
percent of our fuel every 12 years. And so we're not going
to run out of fuel, however there will be other parts of
the system that might limit the lifetime.
JOSH: The prototype system doesn't use nuclear fission.
That's for a future iteration of the concept. For now, it
uses resistance heaters that closely mimic
the heat from fission. The Sterling engine turns
that heat into electricity. Here's how it works...
MIKE: What that simulator does is it heats the coolant and in
this case we're using a coolant that is a mixture of sodium and
potassium, heats that coolant to about 850 Kelvin.
And then that hot coolant is used to provide power to the
sterling power conversion subsystem. And what that does
is it takes a portion of the energy that's in the NaK
Coolant and converts it into electricity.
About 25 percent of that energy is converted from heat to
electricity. Now in the process of that energy being
transferred to the sterling engine, it actually cools the
NaK down. And so that slightly cooler NaK, then goes though
the circuit, it's re-pressurized in a pump and
back through the core stimulator, where it's heated
goes back up and then continues in the circuit.
JOSH: NASA scientists, working with the Department of Energy
think that they could have a nuclear fission based version
of this system in place within 5 to 6 years
Keep track of this project and all of NASA's missions,
at www.nasa.gov.
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