
How the Curiosity Rover's Nuclear Battery Works - peterwwillis
http://www.about-robots.com/curiosity-rover-nuclear-battery.html
======
grecy
Many people here in the far north have extensive solar setups and live
completely off-grid. Unfortunately in winter, we only get ~4 hours of
sunlight, and it's a pain to sweep snow off the panels every day at ~ -30C to
-40C

We don't get much wind, and rivers are only liquid for ~4-5 months, so wind
and hydro are not popular.

I've been investigating commercial thermoelectric couplings as a source in the
winter. Everyone has a BIG wood stove burning 24x7 for ~6 months. My best
research shows it shouldn't be hard to see +400C on the top surface of the
stove. My plan is to have a radiator outside, run anti-freeze in the system
and get an approx 400 deg C temperature drop.

Now, my interest is peaked in this approach from NASA. I wonder how long it
will be until I can buy or build such a thing?

~~~
Erifcit
This might interest you. [http://www.biolitestove.com/campstove/camp-
overview/features...](http://www.biolitestove.com/campstove/camp-
overview/features/)

~~~
grecy
Thanks.

I looked into that a while ago (and a similar one), and it looks like any
power produced from the TEC is considered a bonus, and is in the range of
1-5W, probably only enough to charge a phone, etc.

I'm looking to produce a sustained 150W + to charge deep cycle batteries.

~~~
peterwwillis
Tech specs show the biolite to have about a 2.5in radius and (approx) 6.5in
high fuel compartment, which is about 2.1L
([http://www.wolframalpha.com/input/?i=volume+of+a+vertical+cy...](http://www.wolframalpha.com/input/?i=volume+of+a+vertical+cylinder+with+a+radius+of+2.5+inches+and+height+of+6.5+inches)).
Using its design you can get about 2W _continuous_ power at 5V.

Scaling this up, roughly, you would need about 157.5 liters of fuel space,
though probably much less if your fuel was more compact (obv you don't fill up
exactly 2L of space in the canister while burning twigs). The realistic output
of heat/power based on space is probably much more efficient than something
this large, considering they say 46 grams of fuel can boil 1 liter of water,
and 46 grams is approx 0.046 liters (based on water density).

Somebody please correct my horrible assumptions, but basically, fill an oil
drum up most of the way with wood and build a thermoelectric generator and you
should be good to go.

(Also, if you're charging deep-cycle batteries, i'm assuming you're not going
camping? Maybe solar would be simpler?
<http://www.mdpub.com/SolarPanel/index.html>) (Edit again: I forgot your
original post, no solar)

More edit: Check this page for an adaptable thermoelectric generator:
<http://www.tegpower.com/>

And more edit: <https://www.youtube.com/watch?v=bUH1HA3EnZE> (i'll stop
posting links now!)

------
ScotterC
This concept was also used in russian lighthouses because it would be cold
enough in siberia to create the delta difference needed.
[http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_gen...](http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator#cite_ref-
Ref__4-0)

~~~
TazeTSchnitzel
Some interesting info about safety on this one:
[http://bellona.no/bellona.org/english_import_area/internatio...](http://bellona.no/bellona.org/english_import_area/international/russia/navy/northern_fleet/incidents/37598)
(from Wikipedia citation)

~~~
ScotterC
I'd disagree with the article and say the biggest threat of the RTG's is not
being used by terrorists because a dirty bomb isn't all that effective with
that amount of material, however, a bystander digging into one and having fun
with the material could be a serious problem. Like the Goinia Incident [0].

Then again. It's kind of a funny thing to worry about with all the unexploded
ordinance that's around most countries, even the U.S. I was just out sailing
in the long island sound last week and my girlfriend thought it extremely odd
how many unexploded bombs pockmark the navigation charts.

0: <http://en.wikipedia.org/wiki/Goi%C3%A2nia_accident>

------
DennisP
NASA has almost run out of U238: [http://www.popsci.com/military-aviation-amp-
space/article/20...](http://www.popsci.com/military-aviation-amp-
space/article/2009-09/nasas-plutonium-shortage-threatens-deep-space-
exploration)

People promoting liquid thorium reactors have been pointing out that they
could supply it: <http://flibe-energy.com/products/>

~~~
juiceandjuice
Plutonium 238 is NOT Uranium 238.

There's shitloads of U238 in the world.

~~~
DennisP
Crap, that's what I meant. Thanks.

------
sp332
How much power does the device generate? How much will it generate in 14 years
when it is "expended"?

Edit: Initially 2 kW of thermal power and 125W of electrical power, falling by
only 20% after 14 years.
[https://en.wikipedia.org/wiki/MMRTG#Design_and_specification...](https://en.wikipedia.org/wiki/MMRTG#Design_and_specifications)

~~~
sehugg
According to Wikipedia, 125 watts when it was launched, down to about 100
watts in 14 years.

The JPL guys claim that the RTG is really just a trickle charger for the
batteries that actually handle the load -- which likely has transients that
the thermocouple in the RTG couldn't handle.

I don't know the lifetime of the lithium-ion battery pack but I'm guessing
it'll degrade way before the RTG power decreases below the point where it can
effectively charge the battery.

~~~
bigiain
There's a LiPo technology called "thin film lithium" which is claimed good for
10,000 cycles - assuming one charge/discharge cycle per day (and incorrectly
using earth-days for simplicity), that'd give you ~27 years lifetime from the
battery. (I wonder if this'll end up with the same "over engineered"
reliability that let the Spirit rover last over 6 years when intended for a 90
day mission?)

~~~
i_cannot_hack
The Opportunity rover is still up and running, which means it has exceeded its
planned duration of activity more than thirty times over.

------
stcredzero
[In the voice of old "Gauntlet" game] "About-robots.com needs editing badly!"

 _> The first time I heard about the Curiosity Rover nuclear battery, I was
thinking this must be top notch technology. What a surprised I had when I saw
it has been used for more that 40 years already._

Évariste Galois came up with mathematics in the early 1800's which only in
just the past several decades had widespread applications in cryptography.
Carbon electric arcs were developed right at the start of the 1800's, and not
only have we been finding new applications for them ever since, we'll probably
keep doing so!

Also note that the mid-90's trappings of the digital office were running at
Xerox PARC in the early 1970's.

As is often said: "The future is here, it just hasn't been evenly distributed
yet." There is a lot of "top-notch technology" that the general public doesn't
know about yet, and may not for a decade.

~~~
swalsh
e-ink is another good example. The technology was originally developed in the
70's.

------
joaorj
this article is wrong on many things.

one being that the rover can drive during night.

the small power output of the "nuclear battery" is not used to drive the
rover. it used to recharge batteries during day and night so that the rover
can operate on the batteries during the day.

~~~
mbreese
That's a good point... while in theory is probably _could_ drive at night, it
probably isn't a good idea to have a rover on a different planet driving
around in the dark.

~~~
nnnnnnnn
Is radio communication with the rover even possible at night? We only have
line of sight to mars during the martian daytime.

~~~
digitalsushi
Our line of sight to Mars is independent from Mars seeing the sun.

~~~
danweber
Not really. If the rover is on the side of Mars facing away from the Sun, it's
almost always facing away from the Earth, too, since the Earth is deeper
inside the solar system.

Facing the Earth and facing the sun are highly correlated. Seeing one xor the
other is possible, but unusual.

~~~
saraid216
He's still right in a very technical, strict sense. I'm too lazy to look up
numbers and do the math, but I expect there's a window near the Martian
sunrise/sunset when the sun isn't visible over the horizon and we have line of
sight.

I expect that window is small to the point where no one actually cares. It
would be an interesting applied-math problem for a grade-schooler, though.

~~~
T-hawk
The geometry of viewing Earth in the Martian sky is the same as viewing Venus
in our own Terran sky. The interior planet periodically approaches a certain
maximum angular separation from the Sun. Just as we see Venus but not the Sun
sometimes in the early morning or evening twilight, Martians (and rovers on
Mars) could see Earth but not the Sun at corresponding intervals of Mars'
rotation. It's a significant amount of time, up to several hours per day at
maximum separation.

The angular separation between the Sun and the Earth as seen from a space
probe is significant as far out as Cassini at Saturn. The probe can receive
commands from Earth without the signal being overwhelmed by solar radiation,
except for a few days each (Earth) year when Earth is too close to the Sun as
seen from the spacecraft. (Earth doesn't literally go behind the sun often,
thanks to inclination of the planetary orbits plus Cassini's own inclined
orbit at Saturn.)

> _Our line of sight to Mars is independent from Mars seeing the sun._

Our line of sight to Mars _as an entire body_ is independent, but our line of
sight to a _particular point_ on Mars is indeed correlated with that point
facing the Sun.

~~~
saraid216
Do you happen to have illustrations and/or numbers? I was planning to actually
look everything up and work it out when I got home from work, but it'd be nice
to have confirmation of my results, too.

------
andre
Relevant: INL helps power mission to Mars
[http://www.idahostatesman.com/2012/08/06/2219647/inl-
helps-p...](http://www.idahostatesman.com/2012/08/06/2219647/inl-helps-power-
mission-to-mars.html)

"In simple terms, Curiosity runs, in part, on a $100 million nuclear battery
developed at the lab, said Stephen Johnson, division director of Space Nuclear
Systems and Technology.

The 2-foot-tall, 2-foot in diameter cylinder aboard Curiosity is packed with
radioactive isotopes generating heat. That thermal energy is converted into
the electricity fueling Curiosity's wheels, arms and other gadgets, as well as
recharging its bank of lithium-ion batteries."

"Fuel cells in the energy source are 1 inch tall and 1-inch diameter
cylinders. Each puts out a mind-boggling 9,000 to 10,000 degrees of heat,
shift supervisor Dave Hendricks said."

------
dkkarthik
Wow, that's super cool. I wonder if this technology is being used on any
earth-based applications? If not, I'm assuming there are harmful side effects
that don't necessarily affect the space missions. I'd like to learn more about
the negatives of this technology basically.

~~~
kalleboo
If this is the same tech I remember, Soviet Russia used them a lot for far-
flung lighthouses that couldn't be easily refueled. Many of them are still out
there, or have been stolen, vandalized, stripped of metal by unwitting
thieves, spreading hazard all around. One was even found underwater.

edit: links:

[http://bellona.no/bellona.org/english_import_area/internatio...](http://bellona.no/bellona.org/english_import_area/international/russia/navy/northern_fleet/incidents/37598)

[http://englishrussia.com/2009/01/06/abandoned-russian-
polar-...](http://englishrussia.com/2009/01/06/abandoned-russian-polar-
nuclear-lighthouses/)

~~~
rdtsc
There is a movie on Netflix streaming that has some small plot feature tied to
one of these these nuclear batteries in a far North Russian weather station:

<http://www.imdb.com/title/tt1588875/>

------
Wingman4l7
Calling it a "battery" is disingenuous. An RTG doesn't fit the typical
definition of a battery -- it doesn't store electrical energy. A better name
would be "power supply". _< /pedant>_

~~~
DeepDuh
Well it does - it stores nuclear binding energy that's unstable enough to be
extracted and stable enough to last for x years. It's a nuclear battery just
like convential ones are chemical batteries.

~~~
Wingman4l7
You're not clipping leads to the ends of it and getting current, though --
you're using thermocouples. It's more of a "heat battery", I suppose.

~~~
DeepDuh
And now draw a black box around that whole system. What do you get? A voltage
source, right?

Engineers usually don't care much about the principles of how something is
made. As long as it can be abstracted to a known concept you're all good and
you can integrate it with your given tools, e.g. a combinational circuit plan.

------
jamesmcn
Is a thermocouple more efficient than a Sterling engine, or just more reliable
because of the lack of moving parts?

~~~
sliverstorm
Don't forget more compact. A sterling engine would require a generator, which
in turn means a regulator and a rectifier. Plus, R&R's aren't very reliable
either. When the alternator in your car dies, it's usually the R&R that
failed.

The main disadvantages of thermocouples are cost and efficiency, but cost
isn't a big deal for mega government projects and efficiency isn't a big deal
when the goals are modest (i.e. not flying about like a helicopter) and the
power source is amazing (i.e. nuclear decay)

------
shirro
Given the MSL has a constant power source does that mean it can operate 24hrs
and 40 minutes a day? Do they have driving lights or can drive with IR or
other sensors? If so they could get a lot more science done than the MER
mission. Or do they have to channel the power into heaters each evening?

~~~
wcoenen
> _does that mean it can operate 24hrs and 40 minutes a day?_

Not if it consumes electrical energy from the batteries faster than the MMRTG
replenishes it. Then it needs to "rest" to give the MMRTG a chance to recharge
the batteries.

> _Or do they have to channel the power into heaters each evening?_

Besides 125 watts electric, the MMRTG also continuously outputs 2000 watts of
heat. Heat can be pumped around the rover (either for cooling or heating) to
keep the instruments at optimal temperature [1][2]

[1] <https://www.youtube.com/watch?v=fBtXnug-rgM#t=89s>

[2]
[http://www1.nasa.gov/mission_pages/mars/images/20081209_msl....](http://www1.nasa.gov/mission_pages/mars/images/20081209_msl.html)

------
ilamont
What are the safety implications of launching 10 pounds of plutonium-238 on a
rocket that could malfunction or explode before gaining escape velocity? The
article says the plutonium would not explode, but what about plutonium
particles or radiation entering the atmosphere and ocean?

~~~
jerf
The same safety implications as launching 10 pounds of _anything_ twenty miles
in the air, over an ocean, and subjecting it to an explosion. 10 pounds
divided by any realistic footprint is negligible.

Plutonium is dangerous stuff, sure, but it isn't 10 orders of magnitude more
dangerous than anything else the way some people act like it is. It's just
dangerous, not imbued with an evil malevolent spirit that wants to irradiate
your soul.

Bear in mind the Earth is covered in radioactives; it doesn't take all that
much division before you've got less radioactivity per acre than already
exists naturally, which contrary to apparently popular belief is not 0.

~~~
yk
Per wikipedia[1]:

    
    
      A commonly cited quote by Ralph Nader, states that a pound of plutonium dust spread into the atmosphere would be enough to kill 8 billion people. However, the math shows that one pound of plutonium could kill no more than 2 million people by inhalation. 
    

So no need to worry.

[1]<https://en.wikipedia.org/wiki/Plutonium#Toxicity>

~~~
jerf
You know what the problem with pulling something from Wikipedia is? It has
citations. Specifically, for your pulled quote it cites this:
<http://www.phyast.pitt.edu/~blc/book/chapter13.html> , and the section on
"Plutonium Toxicity" about halfway down the page.

In particular, I commend to you the paragraphs starting with "In response, I
offered to inhale publicly many times as much plutonium as he said was
lethal." But more to my point:

"In summary, a pound of plutonium dispersed in a large city in the most
effective way would cause an average of 19 deaths due to inhaling from the
dust cloud during the first hour or so, with 7 additional deaths due to
resuspension during the first year, and perhaps 1 more death over the
remaining tens of thousands of years it remains in the top layers of soil.
This gives and ultimate total of 27 eventual fatalities per pound of plutonium
dispersed."

I can't quite get a direct cite, but I'm pretty sure the claim that a pound of
plutonium dust can kill two million people is for a pound of plutonium dust
being carefully doled out to two million people in precisely the quantities
that will just barely kill them, because the previous paragraph is the
description of what happens if you just sort of fling it at a city.

And an explosion from a rocket would actually be dispersed over a much larger
area than merely a large city if it were going to hit anybody at all, because
we don't launch anything immediately upwind of large cities. Think state-sized
dispersal and you'd be closer.

"There have been fears expressed that we might contaminate the world with
plutonium. However, a simple calculation show [26] that even if all the
world's electric power were generated by plutonium-fueled reactors, and all of
the plutonium ended up in the top layers of soil, it would not nearly double
the radioactivity already there from natural sources, adding only a tiny
fraction of 1% to the health hazard from that radioactivity."

"I have been closely associated professionally with questions of plutonium
toxicity for several years, and the one thing that mystifies me is why the
antinuclear movement has devoted so much energy to trying to convince the
public that it is an important public health hazard. Those with scientific
background among them must realize that it is a phony issue. There is nothing
in the scientific literature to support their claims. There is nothing
scientifically special about plutonium that would make it more toxic than many
other radioactive elements. Its long half life makes it less dangerous rather
than more dangerous, as is often implied; each radioactive atom can shoot off
only one salvo of radiation, so, for example, if half of them do so within 25
years, as for a material with a 25-year half life, there is a thousand times
more radiation per minute than emissions spread over 25,000 years, as in the
case of plutonium.

"No other element has had its behavior so carefully studied, with innumerable
animal and plant experiments, copious chemical research, careful observation
of exposed humans, environmental monitoring of fallout from bomb tests, and so
on. Lack of information can therefore hardly be an issue. I can only conclude
that the campaign to frighten the public about plutonium toxicity must be
political to the core. Considering the fact that plutonium toxicity is a
strictly scientific question, this is a most reprehensible situation."

And thanks for leading me to the _awesome_ link to post next time this comes
up.

~~~
yk
The quote was pulled to put the "same risk as 10 pound of anything" claim into
perspective, not to give an exhaustive treatment of plutonium ( and
specifically Pu 238) dispersement.

The claim of 2 million cancers per pound of Pu is sketched out just at the
start of the subchapter "Plutonium Toxicity" in your reference, it depends on
a model how long the Pu remains in the lung. ( I suspect Naders number of 8e+9
death is obtained by dividing 1 Pound by an estimate of the lethal dose.)

Additionally the source talks presumably of Pu 239 (at least the numbers in
the appendix are for Pu 239) while the activity ( and therefore the dosage) of
Pu 238 is about a factor of 200 higher. So we can estimate 4000 death per
pound of Pu 238 dispersed in the atmosphere over an city. ( Dispersing over an
Ocean instead of a city would lower this estimate of course considerably. What
could possibly go wrong ...)

And you are welcome, this seems to be one of the better texts one can cite
about the dangers of Pu. (I will be happy to point out the several best case
estimates the text makes.)

------
aik
>> The Curiosity Rover Nuclear Battery will supply the system with constant
power, allowing it to work as much as needed, all year long for as long as 14
years.

Very cool. Massive improvement over the solar panels that only worked during
the day and non-winter times.

------
rogerchucker
Burning question... can a miniature version of this ever be ported to consumer
electronics devices? :-/

~~~
uvdiv
There's a prototype betavoltaic battery which can sustain 50 microwatts on 20
Curies of tritium [1] -- an efficiency of about 2%. Scaling linearly by 10^4,
current technology could get 500 milliwatts on 200 kCi, or 20 grams, enough to
charge a 5 watt-hour phone battery in 10 hours. The tritium cost would be on
the order of $600,000 today [2]. If you could do this, the battery charge time
would be a few decades.

[1]
[http://www.citylabs.net/index.php?option=com_content&vie...](http://www.citylabs.net/index.php?option=com_content&view=article&id=10&Itemid=25)

[2] <http://fire.pppl.gov/fesac_dp_ts_willms.pdf>

------
ktizo
So, when can I get a nuclear car? And what's the insurance gonna cost?

~~~
joshAg
when we start building "breeder" reactors again. Plutonium is a byproduct of
the breeder reactors when they create the type of uranium that can be used for
nuclear bombs (this is one of the reasons that breeder reactors aren't
popular). I was talking with one of the scientists at Ames last night, and
apparently this is pretty much the last of NASA supply, since the US has
significantly cut down on their production of weaponizeable uranium.

~~~
pjscott
That's not really accurate, but rather than explaining why, I'll just give the
abbreviated rundown on plutonium:

Plutonium 238 is a powerful alpha emitter with a half-life of 87.7 years,
making it a great element for powering mars rovers. It's produced by exposing
Neptunium 237 to neutron flux. You can get Np-237 out of nuclear waste from
ordinary reactors. The US has mostly been buying Pu-238 from Russia, but we're
running out, and starting up our own production again is kind of expensive. We
can do it, though.

Plutonium 239 is the kind that gets used in bombs. It's fissile. It's produced
by exposing Uranium 238 ("depleted uranium") to neutron flux in a nuclear
reactor. It's tricky to make weapons-grade Pu-239, because it tends to be
contaminated with Pu-240.

Plutonium 240 is annoying and nobody likes it.

~~~
joshAg
well, i guess i learned not to blindly trust NASA scientists today. thanks for
the info; that was pretty interesting.

