How the Curiosity Rover's Nuclear Battery Works
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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?
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.
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!)
http://www.kickstarter.com/projects/tpod1/tpod1-thermoelectr...
The lethal dose of radiation is about 3-5 Sv, that is 3 to 5 J/ kg absorbed radiation (times some factors, which describe how the radiation is absorbed and which type of radiation). Therefore assuming full body irradiation and gamma particles, the lethal dose for an adult would be received in a matter of minutes ( 60kg irradiated by 1 W would be 1 Sv/minute). Note however, that a more realistic scenario for a dirty bomb from a RTG involves ingestion of alpha emitting particles for a rather large number of bystanders. ( And therefore the effects vary a lot by the details of the bomb and the radio isotopes used. )
So already with the radioactive material from a rather small RTG you can build a quite potent dirty bomb, rather independent of the exact type of the RTG used.
On that note, the idea you're talking about was actually considered for a little while for public use until the dangers were found to outweigh the benefits.
I am wondering if it would be possible to buy or build such a nuclear battery.
In almost every country the materials required are tightly regulated and getting permission even in a lab environment is tough work. If you can work out the legalities and safety, I'd be interested too!
http://www.amazon.com/The-Radioactive-Boy-Scout-Backyard/dp/...
I read the book. from what I remember he started with smoke detectors and worked his way up from there. Just a few letters to some supply houses saying he was a researcher or something. he effectively mail ordered his radioactive sources I think.
Pu-238 isn't naturally occurring, and nobody makes it anymore. The US bought the plutonium that went into the MSL from the Russians, who are starting to run out themselves.
The other problem with RTGs is they get less efficient as they get larger. The one in the MSL only produces 125 watts, which will decay to about 100 watts at the end of its 14 year lifetime. That's not a lot of power.
Thermoelectric generators are far far less efficient than simple generators (say a Stirling engine). The benefit to them is that a) they are very compact and b) they need no mechanical parts.
It makes sense to put a thermoelectric generator in a satellite or rover because the mechanical parts found in a traditional engine are typically very heavy and more likely to fail.
So if you aren't concerned with a couple dozen pounds and the occasionally maintenance call, just use a wood-burning generator. You'll save about an order of magnitude on costs.
edit: what you're looking for is micro-cogeneration (http://en.wikipedia.org/wiki/MicroCHP)
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.
http://www.imdb.com/title/tt1588875/
I enjoyed it a lot - it's got that real bleak outlook that some of my favorite Russian cinema has, and some _spectacular_ cinematography.
People promoting liquid thorium reactors have been pointing out that they could supply it: http://flibe-energy.com/products/
There's shitloads of U238 in the world.
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...
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.
> 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.
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.
Facing the Earth and facing the sun are highly correlated. Seeing one xor the other is possible, but unusual.
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.
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.
Curiosity drives itself.
Edit: Link (communications): http://en.wikipedia.org/wiki/Curiosity_rover#Specifications
Another interesting point brought up was that the rover was tested to 3x life but not to failure. It's certainly possible for it to run for many years longer than the stated life.
"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."
Climbing hills would be easier on Mars.
Given that the batteries store roughly 2.4 kW-h, it's probably safe to assume that the max drive power is less than 500 watts (2.4 kW-h / 10 hours -> 240 watts). Earth side electric vehicles commonly have drive power over 100 kilowatts.
edit: links:
http://bellona.no/bellona.org/english_import_area/internatio...
http://englishrussia.com/2009/01/06/abandoned-russian-polar-...
The main issue is that they're really rather inefficient. The efficiency of the thermocouple at converting thermal->electrical is only about 5-10%, and combined with the cost of shielding, expense of the radioisotope to begin with, and security/safety considerations, they're really only suitable for niche aerospace/defense applications.
Edit: I was curious if anyone had considered a stirling or other heat-engine driven by decay heat, and found https://en.wikipedia.org/wiki/Stirling_Radioisotope_Generato... which looks like it can hit 20+% efficiencies. The downside is that unlike thermo-electric/Seebeck effect converters, they have moving parts that could be a threat to reliability, which is the major issue when you're a planet away from the nearest repair tech.
[1] https://www.orau.org/ptp/collection/Miscellaneous/pacemaker....
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.
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)
AFAIK, No. The battery generates 2kw of heat in addition to the electricity, so I dont think the rover even has any heaters.
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....
Like previous generations of this type of electrical- power generator, the MMRTG is built with several layers of protective material designed to contain its plutonium dioxide fuel in a wide range of po- tential accidents, verified through impact testing. Each MMRTG carries eight individually shielded general purpose heat source modules (compared to 18 modules in the previous generation). The thickness of the protective graphite material in the center of the modules and between the shells of each module in the MMRTG has been increased by 20 percent over previous modules.
However, the same report says there is about a 3% chance of an accident with no release, and a .4% chance of an accident "with release".
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.
It's depressing that the article has to insert (non explosive) next to the plutonium. Clearly some people must think that this is a bomb waiting to go off at any moment.
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.
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.
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.)
And that the US burns around 1 billion tons of coal a year? https://en.wikipedia.org/wiki/Coal
So coal fired powerstations send something like a few thousand tons of Uranium and Thorium into the environment every year (he said, blithely simplifying ppm into "proportion by weight").
Still worried about 10lbs of Plutonium?
We are not talking about nuclear reactors here. Only basic nuclear decay. No criticality. The key thing is the packaging, to make sure you aren't contaminating an area when something goes wrong.
Very cool. Massive improvement over the solar panels that only worked during the day and non-winter times.
[1] http://www.citylabs.net/index.php?option=com_content&vie...
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.
Most commerical enrichment of Uranium uses gas centrifuges to separate the heavier isotopes from the lighter.