
U.S. tests nuclear power system to sustain astronauts on Mars - meri_dian
https://www.reuters.com/article/us-space-nuclear/u-s-tests-nuclear-power-system-to-sustain-astronauts-on-mars-idUSKBN1F72T8
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superkuh
As far as I understand it they are pumping the equivalent thermal energy as an
actual operating core would produce into the reactor casing and assembly using
a specially designed electrical insert that uses external power.

This isn't a fission test. It's a mechanical engineering test. Still cool.

~~~
SigmundA
From my understanding the fission part is "easy", the hard part is taking the
heat and converting to electricity efficiently and reliably.

The Mars Curiosity rover among other probes use a thermocouple based
generators to create electricity from the fission heat[1]. Extremely robust ,
no moving parts, but extremely inefficient just a few percent converted to
electricity the rest to heat. The heat is very useful on mars though due to
the low temps, kinda like your combustion engine in your car, the waste heat
can be used to provide useful heating, but still most needs to be rejected and
it only puts out about 100 watts of electricity.

This new one looks to be striling engine based which means its going to have
much better efficiency since it is a more standard heat engine with moving
parts, prob 20-40%. Hence the higher output. However that comes with much more
complexity and things to go wrong over long term use.

I still wonder if there is much more efficiency to be had from thermocouple's
if the research effort was put into it, it would be similar to solar cell
improvements over the last few decades. You just don't hear about thermocouple
R&D and if it where improved to say a typical solar cell efficiency of 18-20%
it would open all sorts of doors.

1\.
[https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...](https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator)

~~~
tarre
In fact the fission[1] part in such small scale is hard. Curiosity and other
probes using thermonuclear batteries harness alpha decay[2], which is
relatively easy as it happens whether or not you want it to happen, but
creates also much less power. In that case the hard part is to obtain material
with appropriate half-life and other properties. Perhaps best material for
this is Pu-238, which is far more expensive to create than weapons grade
plutonium.

1\.
[https://en.m.wikipedia.org/wiki/Nuclear_fission](https://en.m.wikipedia.org/wiki/Nuclear_fission)

2\.
[https://en.m.wikipedia.org/wiki/Alpha_decay](https://en.m.wikipedia.org/wiki/Alpha_decay)

~~~
theptip
I don't think "thermonuclear" is the right term for the batteries in probes.
Wikipedia says "thermoelectric"[1], as the electricity is generated directly
by thermocouples.

"Thermonuclear" usually refers to the sorts of fusion reactions found in stars
and modern nuclear warheads.

[1]:
[https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...](https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator)

~~~
tarre
Thanks for correction. Unfortunately I'm not able to edit it anymore.

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njarboe
I would love to have more details about this reactor. How much is the total
mass? What is the expected power output over time? What kind of heat sink is
necessary? But in any case this is really cool development.

~~~
T-A
There is a veritable orgy in nuclear tech for space here:

[https://beyondnerva.wordpress.com/](https://beyondnerva.wordpress.com/)

See also

[https://github.com/briligg/moonwards/wiki/Nuclear-
Reactors--...](https://github.com/briligg/moonwards/wiki/Nuclear-Reactors
------Kilopower-\(KRUSTY\))

------
baron816
What happens if the launch rocket fails? That’s been the main concern of
sending nuclear reactors into space thus far, right? Has this been addressed
here?

~~~
njarboe
It is too bad that most people are so afraid of anything nuclear. I hate to
say it, but maybe people working on nuclear power need to change the name.
Isotopic power would have pretty bland associations.

Uranium 235 is a very low level radioactive metal. Even if the rocket blew up,
the isotopic fuel would remain intact (that is, not vaporized into breathable
particles). The radioactivity from a Uranium 235 isotopic reactor comes after
the reactor has been running for some period of time (from byproducts of the
nuclear reaction), not the original fuel itself.

~~~
stevedonovan
Consider the thermal Plutonium power sources that have been sent on outer
Solar System missions. One of those crashing is a much more serious problem
than a new U-235 reactor, since Plutonium is very toxic.

~~~
garmaine
Plutonium isn't toxic, not any more than any other heavy metal.

~~~
ttul
It is radiotoxic

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garmaine
Nope, it is not. Not anymore than the straight radiation you would get from
it.

When you talk of radiatoxicity what is usually meant is the hot particle
theory which says that a bit of radioactive material lodged in one place is
more likely to cause cancer, because the radiation given off repeatedly hits
the same tissue. It turns out that in cohort studies done this is not true.
Specifically people who have inhaled plutonium, an inadvisable thing to do,
actually have lower rates of lung cancer.

Pu-238 has some radioactivity, although not as much as many fission products.
Radioactivity is bad. But the fear over plutonium toxicity is actually
overblown beyond the baseline radioactive dose it provides.

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yellowapple
If each core really is the size of a paper towel roll, then this seems like a
solid step toward me eventually owning a nuclear-powered car.

~~~
feliix42
This oddly reminds me of the story of Fallout.

[https://en.wikipedia.org/wiki/Fallout_(series)#Setting](https://en.wikipedia.org/wiki/Fallout_\(series\)#Setting)

~~~
maushu
I love the story of Fallout. They decided to use nuclear reactors on cars
because there as a lack of petroleum. It was too late though since the Great
War started (and ended) a couple of years later.

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ifdefdebug
I find it frustrating NASA talking about putting people on Mars but if you
look at reality, it can't even put astronauts in the orbit anymore. What about
solving that problem first, and when it's done, then we can dream about
Mars...

Or are we going to outsource such mundane tasks like manned orbital space
flight to the Russians and Chinese forever, while we are proudly preparing the
colonization of Mars? /s

~~~
imglorp
I find it encouraging the private sector is filling the gap. Musk's vision is
clear if you assemble all the pieces his companies have built on Mars: solar
and battery power, tunnel boring for both shelter, water, and air (which could
imply return fuel he can do O2+H2).

Solar might not be the most efficient for Mars, but he can bring tons of it
without messing with nuclear politics and PR. Note also the Boring Company TBM
diameter is less than the BFS. Don't be surprised if a TBM one of the first
payloads.

[https://en.wikipedia.org/wiki/SpaceX_Mars_transportation_inf...](https://en.wikipedia.org/wiki/SpaceX_Mars_transportation_infrastructure#Passenger_spaceship)

[https://www.boringcompany.com/faq/](https://www.boringcompany.com/faq/)

~~~
Balgair
I agree that Elon's companies do have suspiciously many things to do with Mars
habitats.

However, the reliability of the tech we have is _severely_ lacking. To get off
Mars, you are going to need a rocket. So then you need to land a rocket on
Mars.

Fully fueled.

You also need a backup. We simply do not have that kind of reliability yet,
and I don't think we're even close.

Fine, we'll fuel it _on Mars_. That means a remote robotic mining-facility and
rocket-fuel-plant, in nearly no atmosphere, in cold temps, up to 16 light-
minutes away (at worst, true). So it's gotta be totally autonomous. And not
explode while people are in transit. And it's likely going be on a pole, so
that you have easy access to fuelstuffs. Which is boring as all heck compared
to Valles Marianas (not a big deal, admittedly)

If we have that tech on Mars, then the economy of Earth is going to look a LOT
different. Self-driving cars aren't the half of it.

Mars, in a nutshell, is VERY Hard.

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ourmandave
Unanswered in article:

How long does the power unit lasts until you have to replace the paper-towel-
roll-sized U-235 core? Where are they going to put the old ones?

What's the plug interface? Can I charge my iPhone? What about my electric
razor?

Are they going to test burying one in red sand for 15+ years and see if it can
be dug up to phone home in an emergency?

~~~
SideburnsOfDoom
And in 15 years, do you need to import a new core from Earth or what - have a
uranium mining and refining operation up and running by then?

~~~
jessriedel
Enriched uranium is one of the few supplies for which it's probably
economically sustainable to provide continuously from Earth.

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kristianp
Part of Nasa's Game Changing Development program:

[https://www.nasa.gov/directorates/spacetech/game_changing_de...](https://www.nasa.gov/directorates/spacetech/game_changing_development/index.html)

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MikeWazowski
_" Testing on components of the system, dubbed KRUSTY..._"

Named after Krusty the Clown?

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donarb
KRUSTY stands for "Kilopower Reactor Using Stirling TechnologY".

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wbl
That's a retronym. Earlier tests in the series were named DUFF.

~~~
chiph
At least they didn't name it HOMER. You don't want that guy in charge of a
nuclear reactor.

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vadimberman
I'm curious, where does one get the nuclear fuel on Mars? Does it have to be
flown all the way from the Earth?

~~~
acidburnNSA
Definitely. You can probably mine uranium on Mars but that would require a
bunch of infrastructure and other power sources. These babys are way down-
rated so they can run on a single loading of fuel for decades, like nuclear
submarines. Good old E=MC^2.

~~~
jacobush
I don't think there is any uranium to be had there. For such heavy elements to
get deposited in ore near the surface takes special circumstances, such as
those of Earth.

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schiffern
What pertinent "special circumstances" do you mean?

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fhood
Tectonic activety I suspect.

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quotemstr
Tharsis region?

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fhood
When was anything there last active?

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quotemstr
Does it matter? It's not as if the deposits migrate.

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jhayward
On Earth they certainly do, if you choose the right time scale.

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quotemstr
Right, because the Earth has tectonic activity. Mars? Not so much. Geology
should have been stable over the 500 million years since Mars last had
significant geological activity.

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davedx
How will they cool it?

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InclinedPlane
It's radiatively cooled, just as RTGs are.

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mikaelgyth
I want one!

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alangibson
This thread is a great example of why I love HN. I clicked on Comments
expecting to see a bunch of "nuclear = devils energy" posts, but what I found
was reasoned discussion weighing the real pros and cons of this particular use
case.

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aurelianito
Q

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lmilcin
I am not sure this is a good idea.

Nuclear reactor is an easy way out of a problem that has alternative
solutions. Restriction on using nuclear power for previous missions did a lot
of good in terms of researching and perfecting the alternatives (solar
arrays).

Restricting the use of nuclear power does not prevent missions, it only adds
to the cost of the mission, which is not really a technical problem.

Maybe launching one, fresh, yet inert reactor, is not a big issue. The issue
starts when we fly a lot of them and they start falling back to Earth after
some service time.

It is relatively easy to build safe reactors on Earth (if only everybody was
interested in safety and not their own agenda). It is much more difficult when
you are going to shoot the entire device into space and you can't have 1000:1
of shields and casings.

~~~
icelancer
There is essentially no actual ecological or serious fear about these devices.
The weapons ban was meant to help avoid nuclear exchange between nations;
there's very little scientific data that shows there's added cost or risk of
thousands of reactors falling to Earth and causing radiation poisoning.

Nuclear is exceptionally safe and all the recent accidents (and ones in the
past, really) are all due to human stupidity and bypassing several failsafes.
You can argue that's an issue that will never go away, and that's true in the
absolute sense, but it's not a nuclear problem. It's a human issue. We're
holding ourselves back for scientific research because of arbitrary issues;
and the weapons test ban didn't even solve nuclear proliferation anyway.

Solar won't be held back because nuclear is finally an option. They serve two
different purposes entirely.

~~~
7952
> It's a human issue.

Which could be applied to any challenge that humanity face. This basic human
weaknesses is always what holds us back in any endeavour. It is dangerous to
just dismiss it as "arbitary". You have to deal with these issues if you want
to make big projects achieve their objectives.

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nine_k
It's fine to put yourself to a danger willingly. It's not fine to put your
neighbors to a danger without their consent.

The problem with many pieces of large-scale tech is potential harmful side
effects on unrelated people who did not ask for that.

~~~
7952
Yes, I agree. People are often nonchalant about those low probability dangers.
But a single death from Cancer is just as bad as the death of an astronaut,
perhaps worse as they have not consented to the risk or understand it. We
should care about that, especially as space exploration is such an optional
undertaking which people don't have to support. That is why there is a range
safety system and why anything radioactive needs to be treated with caution.

