From a technology standpoint, there's not too many greater challenges than nuclear power
in space.
The physics involved in it is quite intense — it has that luster of something totally
different.
We start with that highly enriched core, the splitting of the atoms generates that heat
that we need at the right power levels, at the right temperature levels, and then we
transfer that heat up to the power conversion system.
You convert that to electricity at that engine, reject some of the waste heat, and then use
the electricity for whatever you're trying to power, whether it's a coffee maker or a
very expensive instrument for science.
It sounds pretty simple because it kind of is simple.
It's just the engineering pieces aren't always simple.
Nuclear energy and space flight have a deep history that stretches all the way back to
the Cold War.
At the time, scientists were looking for new ways to harness the power of the atom, and
nuclear offered something special for deep-space missions.
We don't have to rely on the sun.
When we go out in deep space or whether we're in a shadowed crater on the moon or whatever,
we've got our own energy source.
That's the biggest plus.
The secondary piece of that is the amount of power that energy can provide.
Fission power is very, very high on the power density scale.
As a quick refresher, nuclear fission releases heat energy by splitting atoms, and fusion
combines two lighter atoms into a larger one.
They both release an enormous amount of energy, but scientists found fission easier to control
for space missions.
To tap into nuclear’s potential, NASA launched a research program called SNAP.
This kickstarted the development of radioisotope thermoelectric generators, which use plutonium-238
and thermocouples to convert heat into electricity.
These units have been on a number of famous missions like Curiosity, Cassini, Pioneer,
and even Voyager 1, which is currently cruising on RTG power 21 billion kilometers away from
us.
The program also developed SNAP 10A, a fission reactor that’s considered the U.S.’s first
and only known nuclear space reactor.
It took off in 1965, failed after 43 days into the mission, and will be orbiting Earth
for another 3,000 years.
All subsequent nuclear space programs, like NERVA, which looked into nuclear powered rockets,
were shuttered or just didn’t get off the ground.
Now, given, they were working on bigger power systems, which was part of the problem, I
think.
But, they were also chasing materials and processes and things that weren't available
at the time.
Today, nuclear power systems are seeing a comeback, and that’s thanks to new mission
targets.
When we start talking about putting men on the moon in 2024 or on Mars in the 2030’s,
you need a lot more power.
That's where fission really kicks in.
Kilopower, is one to ten kilowatts of electrical power.
That’s starting with the fuel source.
It's uranium, molybdenum alloy fuel.
Highly enriched.
We have sodium heat pipes that are attached to that core.
That sodium heat pipe carries that heated vapor up to the Stirling power conversion
system, and then we have to cool the cold side of the engines to get that temperature
difference that we need for that power conversion and keep the engines from overheating.
The other pieces of the reactor that are, obviously, very important are the neutron
reflector.
That helps direct those neutrons back into the core and keep that chain reaction going
at the power levels that we need.
Before operating this, we have a poison rod inside the center of that core and then, when
we get to our destination we have a mechanism that would pull that rod out, make sure that
those neutrons will not be absorbed anymore and they can start the actual chain reaction
that we need.
One of the biggest attributes, I think, to the success of this program was that we kept
everything very small.
And, we're looking to make it as lightweight as possible.
Once the design was approved by NASA, the system and the people behind it were shipped
off to Nevada for testing.
KRUSTY was the experiment, which stood for Kilopower reactor using Stirling technology.
That experiment was really a follow-on to the Duff experiment, a demonstration using
flat top fissions.
Los Alamos, typically, or always likes to name their nuclear experiments after Simpsons'
characters.
We run through all those mission scenarios, where we would turn off the cooling to the
whole top end of the power conversion system and see how the reactor reacted.
And then, how we could really mess with them and see is it going to be a stable controlled
reactor.
The experiment culminated in a 28-hour test, from reactor startup to shutdown.
It operated at 800 degrees Celsius and produced over 4 kilowatts of power.
The highest power nuclear mission we've ever completed was Cassini, that had 870 watts.
So, already our lowest is already higher than any mission that's ever been done.
We did things to that reactor that you shouldn't do to a reactor, but it was really neat the
way it handles.
From concept to test was about three and a half years.
That's a real quick timetable.
To me, that's the most impressive piece.
Me and one of my buddies down at Marshall, as we were cleaning things up afterwards.
You know, the thousands of CAD models that we had and the information that was generated,
we're like, how did we do all that work?
I'm like, I don't know.
Some days, I don't know.
We worked a lot of hours and just had a lot of passion.
The fact that it worked really well was just a bonus.
This was a major step in demonstrating nuclear power’s feasibility in the new space age,
but there are still hurdles ahead.
The real challenges are really political and how we develop all the safety and security
pieces to launching a nuclear system.
There's a whole lot of work related to making sure that there's no way you accidentally
start that reactor up.
And then there's what we call the launch safety piece, which also has a criticality accident
associated with it, so if the launch vehicle fails, and it falls into the ocean or on a
beach or in the general public, we have to show that it's not going to turn itself on.
Political will might be in favor this time.
Congress recently passed a bill earmarking $100 million for NASA to develop nuclear thermal
rocket engines.
So a future of fission, for both propulsion and power, is looking ever more promising.
We've just finished some studies with JPL on how we use this for what we call nuclear
electric propulsion.
So, you couple our reactor with an electric propulsion system and we can go do deep space
missions, carrying much higher payloads, faster times.
We've got design concepts that couple four of those to give us forty kilowatts electricity
on one lander that now you can use for your human habitat.
Once we improve the technology and it's available as a power source, you'll start to see some
really neat propulsions on what they can do with that extra power.