I've been wondering if tritium could be used as an alternative power source for the nuclear batteries used on space missions. Of course tritium has to be "manufactured" just like plutonium-238, but on the other hand it can be made from lithium using a fusion reactor [1].
But wait, you're thinking, fusion reactors based on current technology consume more energy than they can produce. That's true, but also irrelevant if your business model is producing tritium rather than energy. This is because the going rate for tritium (according to Wikipedia) is something like $30,000 per gram [2].
I'm not sure what the licensing requirements are on fusion reactors, but I think they're a lot less onerous than licensing a new fission reactor. I don't think there's any licensing requirement at all for a small fusion reactor like a Farnsworth fusor.
Disclaimer: This is just idle speculation because I haven't done the math.
Nuclear 'batteries' are radioisotope thermoelectric generators (RTGs). They require a pretty substantial amount of heat to produce electricity. I don't know about temperatures, but tritium produces a decay energy of 0.018590 MeV, versus plutonium-238's 5.593 MeV. Assuming you can scale it up directly, the 4.8kg of plutonium-238 in Curiosity would be equivalent to 1444kg of tritium. It's just way, way less energy dense.
Edit: This explanation is way, way off. See response from 'throwaway_yy2Di
There's two other differences you'd need to account for:
* One Pu-238 nucleus weighs 238 amu; a triton only weighs 3 amu
* Tritium decays 7 times faster -- a 12.32 year half-life, vs. 87.7 years for Pu-238
Put together, the specific power (watts/kg) of pure tritium is about twice as high. That's chemically just hydrogen gas, which I'd guess isn't practical. The solids with the highest hydrogen density, like polyethylene ([C2H4]n), would be less power-dense, but not by much.
But I think there's some slack here. The ESA is designing their future RTGs to use Americium-241, which is drastically worse (in terms of these figures), yet still usable.
Maybe the biggest drawback for tritium is the decay energy of 0.02 MeV compared to 5 MeV of Pu238. On longer missions also half-life may create problems (12 years / 70 years).
That's a good point. Of course if you can produce tritium cheap enough it might be feasible to just start each mission with a grossly over-powered nuclear battery.
We may have to reconsider some aspects of non-proliferation for the sake of space exploration. Not just for nuclear batteries, but also for things like Project Orion which tried nuclear propulsion.
Orion is a really cool concept and it's a lot of fun to think about, but realistically any space propulsion system that horribly contaminates the atmosphere and fries every satellite anywhere near Earth is not an option.
It's not really useful for the type of spacecraft we use today, but if you assemble the spacecraft in orbit and only use the nuclear propulsion once you are far enough away from satellites it looks great for gigantic payloads or very high speeds.
You lose much of the advantage of Orion, since Orion is extremely heavy, and you're doing the hardest part of the work without it. You also have to wait until you're pretty far away from Earth, not just out of the atmosphere, before you start blowing up nukes unless you want to destroy all electronics in sight.
>any space propulsion system that horribly contaminates the atmosphere
Modern nukes are very clean. Even in the 70s, we had nukes that were up to 98% efficient. I can't find the numbers for newer bombs, but they are even cleaner.
High efficiency just means you're not leaving lots of uranium and plutonium behind. You're still leaving lots of fission products, and lots of neutron-activated materials from the non-nuclear components of the bomb.
There's a reason that testing nuclear devices in the atmosphere is frowned upon these days.
Doesn't Plutonium-238 occurs naturally along the Thorium decay chain? I believe that it's fairly easy (relatively speaking) to capture 238 from the Thorium nuclear reactor process.
A Thorium-based nuclear reactor prototype has already been successfully run for years at Oakridge National Laboratory- seeing the value of Plutonium-238, it might justify the cost of building a full grade Pu238-extraction nuclear reactor.
I've consistently heard the following two claims about thorium reactors:
1. They offer a number of advantages in safety, efficiency, input materials, byproducts. No comparative disadvantages.
2. The United States is not actively pursuing any plans to implement thorium reactors.
Is the above really true, or are there some comparative disadvantages to a Thorium reactor vs a traditional nuclear reactor? If the above is true, there must be some conflict of interest (imagine that, a conflict of interest in the domain of energy!) causing #2. Is there a legal issue?
From what I have read, the best traditional fission plant designs are very safe, efficient, and produce few byproducts. It's the older plants that have problems but we have learned from them and made improvements.
Compared to the most state-of-the-art plant, thorium reactors are not significantly better and we have years of first-hand experience with traditional uranium reactors and very little with liquid fluoride thorium reactors so the incentives to start at square 1 with an new technology are small.
So the good news is if we ever got over our irrational fear of nuclear power, we have time-tested plans for safe, clean and efficient power plants ready to be built.
From what I've read it's not a legal issue, it's a "huge amount of money needed to get thorium reactors to where they need to be" issue. Nobody is really interest in putting up that money because current modern reactors are "good enough" - all the problems with nuclear plants tend to come from old, bad ones that are decades behind the state of the art.
From what I've read, the reason for #2 is historical. You cannot make bombs with thorium reactors, and when bombs were being made is when most of the advances in nuclear power were made. Since then a number of accidents at nuclear power plants have rendered any advancements in nuclear power taboo in the US so there is no development, especially not in anything new nuclear-wise.
A mix of politics, historical nuclear industry in-fighting, 9/11-terrorism-godzilla paranoia and oil industry lobbying make nuclear development very difficult.
It's also made nuclear power one of the safest and cleanest sources of power in the States.
China and India are very aggressively pursuing Thorium reactors though, which risks putting the West at another energy competitive disadvantage within decades.
My understanding is that thorium reactors have a bit of a chicken and the egg problem.
We've got plenty of experience building more traditional nuclear designs - considering how conservative and concerned the masses tend to be when it comes to nuclear technology (not entirely unreasonably), do you want to be the one "risking" it on an "unproven" reactor design? It's politically tricky, in an age when several countries are phasing out nuclear power entirely in a knee-jerk reaction to Fukushima.
Even ignoring political risk, I'd imagine there's some budgetary risk for investing in the "cutting edge" of nuclear tech - more room for new mistakes to be made, additional complications to be discovered, resulting in budget overruns.
I believe China is investing in building thorium reactors. It wouldn't surprise me if at some point in the future, the US is left in the position of poaching nuclear talent from China to play catch up in the thorium reactor department.
No, the naturally abundant isotope of Thorium has 6 fewer nucleons. Why would building a special reactor for a program that has so little funding be justifiable?
Because along with a steady source of Pu238, you also get the benefit of a safer, smaller nuclear reactor using a fuel that is significantly more common and less weaponizable than uranium/plutonium.
Please provide evidence that a Thorium reactor is safer. We have the means to make all the 238Pu we want. NASA just needs to pay commercial reactor operators to irradiate 237Np targets. This is a big problem, because NASA has very little funding to accomplish this, and the target material comes in a purified form suitable for direct use in nuclear weapons.
I'm a nuclear safety analyst. I need more than a powerpoint to convince me that an untested technology is safer than a technology that has seen billions of dollars of investment in enhanced technology, engineering, modeling, etc; along with decades of lessons learned. I'm not saying it couldn't be, but I think there are better ways to spend money on nuclear energy technologies right now, in terms of carbon offset and prevention of radioactivity release.
Is it practical to irradiate the target in units of mass that are smaller than the critical mass?
(The thought being that you can then only allow one unit to be in transit from storage to a reactor at any given time, pretty much entirely mitigating the risk of someone gathering enough of it to make a bomb)
The Nature article that PopSci links to goes way more in depth and is a great read: http://www.nature.com/news/nuclear-power-desperately-seeking.... Also brings up discussion of the need of much more powerful energy sources (potentially nuclear) for proposed human space exploration missions.
If people (politicians, and public) would just get rid of their prejudices and we could just develop a nuclear reactor for outer system exploration and be done with it...
Fuel would not be such a pain to manufacture, there'd be oodles of more power available (more bandwidth for communications, nuclear electric propulsion for faster travel times), and the reactor would be just as safe, if not safer to lift to orbit (unused nuclear fuel is not radioactive, Pu-238 is, although it's so well sealed that it's practically impossible to free it to environment on an accident).
I wonder if for activities near the gas giants the massive Magnetospheres could be tapped for energy as the satellites move through them. However over time you'd be trading orbital elevation for energy.
Another great side effect of RTG's is the "waste" heat keeps your electronics from freezing in the deep of space.
The problem is that the production methodologies for Pu-238 are ridiculous and have a ridiculous number of volatile critical dependencies in both the creation and harvesting process.
"This has been the method of choice at the Department of Energy's Savannah River Site (SRS) production reactors. However, there are several shortcomings with this method of production. First, the production efficiency is quite limited, i.e., to approximately 13% efficiency. This is seen from the fact that the Pu-238 produced in the target after only 2.12 day's half-life decay, itself becomes a target for production of higher isotopes of plutonium, thus reducing the Pu-238 purity by producing Pu-239 and Pu-240. Second, this process produce a hazardous Pu-236 by-product. As noted on the decay chain, above, there is a η→2η or γ→η reaction that results in the production of Uranium-236 (U-236) and Pu-236. These reactions increase with exposure to fast neutron flux. Pu-236 decays to U-232, which has a hazardous gamma-ray energy emitting daughter product. Even a few parts per million U-232 increase the radiation exposure hazard to personnel dramatically. Lastly, Np-237 must be chemically purified before target fabrication. This is seen from the fact that Np-237 decays to Protactinium-233 (Pa-233), which in turn has a strong gamma-ray emission with its beta decay to U-233 (half-life 27 days). Therefore, the Np-237 was stored in solution at SRS and chemically processed immediately before fabricating targets. Solution storage of Np-237 may not be practical at an alternate production site."
The extent to which this should worry our interstellar concerns is huge. The voyager 1 went several billion kilometers away from the Sun. You know it's crazy, it's so far away that it takes 15-20 hours for the signal to reach us.
The voyager 1 is probably going to go out in like 2020, but that's because of the Plutonium- 238.
There's 2 sites in the USA that can produce it.
Hanford in Washington State and Savannah River Site in South Carolina.
The Russians have Mayak, and thank goodness they kept making the stuff.
Hopefully we can pump some steroidal funding into High Flux Isotope Reactors.
I've been watching this issue since 2006. In 2009, someone finally spoke up about it and published some papers on it.
238Pu is always going to be problematic because of the fact that the target material is only available in the US in weapons-grade form. USG moved all of it to secure storage at INL, and are very cautious about any program to transport it for 238Pu production. Hopefully they can get ATR moving and keep missions supplied.
Was lucky enough to get to see Dave Lavery (Program Executive for Solar System Exploration at NASA) speak about Curiosity a year or so back; on the Rover's radioisotope thermoelectric generator, he mentioned that these devices come as a complete package from the DoE (so Nasa had little say in the power characteristics, for example, which constrained what they could do with it), and that technically they are 'on loan' to Nasa.
The DoE has no plans, so far as I'm aware, to go and get the one on Curiosity back when Nasa's finished with it.
That's the real mission for those unmanned boeing test spacecraft - they are the precursors and work-in-progress test craft for the classified military project to reach Mars 10 years before current estimates of civilian efforts (including NASA) in order to retrieve the generator from the rovers.
Realistically, any form of power generation could be used in space. It's really only a question of whether it's financially and practically feasible.
I've been interested to see if Liquid Flouride Thorium Reactors (LFTRs) ever become a thing.
From what I've read about LFTRs, they can produce a whole lot of power- the most efficient system produces 1000-MW(e) from 700kg of fuel.
That lasts approximately 12.5 years, give or take.
Obviously, thats on an Earth-based system and most spacecraft probably don't need anywhere close to 1GW.
Pu-238 has the highest energy density which is why its so useful (both as a weapon and an energy source). Its the cheapest to use because it adds the least amount of weight to the launch vehicle.
> "Realistically, any form of power generation could be used in space. It's really only a question of whether it's financially and practically feasible."
Are you referring only to nuclear power sources? Because a literal reading of your comment ("any form of power generation") is obviously silly (e.g. steam power). And questions of financial and practical feasibility are two of the most important considerations for nuclear power systems, so one shouldn't dismiss those concerns so easily.
Closed loop steam power is actually not that unreasonable in space.
Concentrated solar cells have been considered for a range of space operations. They generate a lot of waste heat, which opens the way for a range of heat engines. Currently, non concentrated solar is a clear winner but serious effort went into studying combined systems.
Long term several space mining concepts involve using concentrated sunlight to heat and refine asteroids. This would tend to make quite a bit of waste heat and steam power is one method to utilize that waste heat.
As long as it doesn't have any (constantly) moving parts, doesn't have requirements relating to pressure or radiation exposure, works in a variety of temperatures, it could be used.
Solar panels and RTGs fit the bill today. Maybe the ASRGs have moving parts, given their name?
Thorium reactors may be useful on earth. But the hype is misplaced for space probes. Either they need maintenance (extracting fission products from the fuel) or closed cycle processing which makes them quite bulky (by space mission standards, not by nuclear reactor standards).
RTGs and stirling engines are fairly lightweight and compact. reactors provide more power per weight, but they have a much higher minimum weight.
And molten salts aren't exactly the most hassle-free technology there is. they are highly corrosive, so you have to compromise on the materials you use and it also strongly limits their lifetimes.
RTGs on the other hand often operate long beyond their intended lifetime, albeit at reduced capacity.
>I think the issue with Stirling Engines is the fact that they have moving parts that could wear and break down.
In NASA's ASRG design there is a stirling generator with only has one moving part: a free piston moving inside a coil, cushioned by the working gas. Wear and tear should be minimal, even for a multi-decade mission.
Yes, but I was comparing to molten salt reactors. Stirling engines are still much simpler than reactors, even if they are slightly more complicated than RTGs.
AIUI they already have research models that are capable of running for decades without maintenance.
I worked for about a year and a half on the ASRG project, specifically doing reliability work for the Stirling engines. They had a bit of a ways to go to prove out the system (its a tricky problem trying to "prove" that your device will last 17 years), but they had made a whole lot of progress. The biggest problem for the project though was that the ASRG wasnt being designed for any one mission, so its performance requirements were a bit of a moving target.
Another aspect of this that the article fails to mention is that NASA has tried to come up with more efficient thermo-acoustic energy converters than the existing seebeck-effect RTG's for radioactive sources [1], but the projects went terribly over budget and got cancelled.
If I beam 1 GigaWatt to Jupiter from Earth at closest approach, with the same beam divergence as current moon-shooting laser technology, they could gather at 0.10655 W/m^2.. so terrible. Truly RTG FTW.
The article mentions other batteries that can use the existing Plutonium 238 more efficiently, but is it not possible to design a battery/generator that runs on an alternative nuclear fuel source?
Linkbait headline. As this article itself (last line) alludes to, production of plutonium-238 has restarted[0]. So we have enough for three more batteries, but are producing more...
well, they have one to use half a decade from now (2020), two more in reserve, and per your statement, they can make one per decade. Seems they are doing fine!
If any nuclear material could be easily turned into any other nuclear material, life would be so much easier, and nuclear waste would be much less of a problem. ;)
We changed the title to the last sentence of the article, which seems to make its point more neutrally. If anyone suggests a better (more accurate and neutral) title, we can change it again.
it's not a linkbait title, it's a really weird one (mixing registers/i.e. level of formality.) It sounds like someone setting their foot down, informally.
The money that would have gone to such missions would be much better spent on solving problems closer to home, like reducing the effects of climate change.
And it almost certainly would not have been spent on those things even if the missions were cancelled.
It's like getting angry at software companies because they're not spending all their profits on solving climate change. The existence of a problem doesn't mean that the entirety of society and technological progress must pause until it's solved.
This concept of "drop everything and study only the most 'important' areas" is misguided. Research doesn't work that way.
There are already an enormous number of talent scientists studying climate change, how would putting nuclear battery scientists on this project help? Are climate scientists short on resources? Better yet are they short on resources because NASA wants to produce nuclear batteries.
Finally there is the concept of cross pollination and random discovery. For example, CERN scientists invented the modern cell phone touch screen, super conductivity was discovered by accident, methods developed by materials scientists to study liquids is used in robotics. You kill off this kind of creativity and random advancement as you narrow the scope of scientists.
Or they could take that same amount of money away from things that aren't furthering knowledge of the universe and research that leads to new advancements that historically have had a rather impressive impact on the technology available to the average person.
You know like from military minded funding, hell that amount would barely make an impact there. Especially since more efficient safer nuclear power, which continued research into nuclear battery construction could potentially contribute to, could itself help provide a source of power to help slow climate change.
I actually "know" a guy ( old Usenet contact, current Facebook friend ) and he's savvy enough to explain the models to me. I don't understand them, but I can kinda sorta get a little bit about it - they depend on theorems and assumptions that, if I started now, I might get to the bottom of before I die. The knowledge gap here is staggering. I just don't have that kind of training and bandwidth.
Basically, I sort of have to trust him. That's not the same thing as "knowing".
No, he won't write That Book; I asked. He doesn't have the time. He has grad students that do have the time, but they're busy doing something else.
I am unusually lucky in that regard. And fossil fuels are pretty important as a replacement for animal - and human - muscle power, historically.
It's less activists than ordinary people going "Lol, whut?". And if, as I see it, there's a skirmish line between the industries that make carbon-causing things and ... "science", it's not reasonable to expect the carbon-people to all just get shot and lay down.
This is looking more and more like a "smoking" thing, and that didn't turn out so well. I know people of low income who smoke, and the taxes hurt them. They already live close to the edge. You and I don't get to tell them to quit; that's up to them.
I am not even a "doubter" but don't ask me to show my work. So I can hardly throw rocks at people who draw a different conclusion.
> It's less activists than ordinary people going "Lol, whut?".
The activists are the ones telling ordinary people "scientists disagree and there's no consensus" when the reality is it's fundamentally settled science. The same occurs with evolution.
> I know people of low income who smoke, and the taxes hurt them.
Smoking is actually a great example to use here. Same situation as climate change - right-wing lobbying groups (some like the AEI are now engaged in the climate change "controversy") funded by industry succeeded for decades in muddying the waters and making it look like the science wasn't yet settled.
Sure. So ignore the activists, outside of publishing stuff to make your point. My point is it'll all go adversarial and that'll be more heat than light. I am still waiting on the book 'AGW for Dummies' that people who want to make the point can use as a reference. There are a handful of places on the Web that are pretty good, but it's not enough.
I don't like the appeal to consensus. Give people the tools and let them make up their own minds.
Smoking is a terrible thing to use as an example. "Whoemever" is aiming at the lobbyists and hitting people who have no dog in the fight and just can't, or won't, quit smoking. The companies were not alone in this; they had millions of customers. Still do.
There was a component of the thing that was about truth. but that passed a long time ago. Now it's just about winning or losing. Here's hoping I'm wrong and AGW doesn't go the same way.
Aren't things divided enough yet? "When elephants fight, it is the grass gets trampled".
> So ignore the activists, outside of publishing stuff to make your point.
That's been tried, and it results in them getting their misinformation heard by the public (who simply don't have the scientific knowledge to figure out it's bullshit) without a counter-argument. See: anti-vaccination movement.
> I don't like the appeal to consensus. Give people the tools and let them make up their own minds.
One of the tools necessary is a graduate-level education in the topics at hand. I don't get to do my own cancer treatment or prescribe myself lab tests for the same reasons random yahoos shouldn't get to evaluate climate science - we don't have the requisite training and knowledge. That's why we have experts, who nearly unanimously agree.
> The companies were not alone in this; they had millions of customers. Still do.
And the taxes are intended, in part, to prevent new customers. Teenagers pause a bit at the idea of picking up a $10/day habit.
I fail to see how this is good? These batteries are being sent into space to explore our solar system. Without them powering some of these spacecraft becomes extremely difficult or impossible.
There is some opposition to using nuclear material on space missions, since space travel isn't safe. The biggest fear would be a rocket blowing up at some perfect point in the launch to end up spreading plutonium-238 over a wide area.
I don't think that fear is in the end warranted, but as fears of such things go, it is more justified than many.
I could only find 5 cases where a space craft carrying an RTG suffered a mishap. of those only 2 resulted in the release of radiation. Both of those were in the 60s.
from Wikipedia:
To minimize the risk of the radioactive material being released, the fuel is stored in individual modular units with their own heat shielding. They are surrounded by a layer of iridium metal and encased in high-strength graphite blocks. These two materials are corrosion- and heat-resistant. Surrounding the graphite blocks is an aeroshell, designed to protect the entire assembly against the heat of reentering the Earth's atmosphere. The plutonium fuel is also stored in a ceramic form that is heat-resistant, minimising the risk of vaporization and aerosolization. The ceramic is also highly insoluble.
it also notes that the LEM on Apollo 13 carried a RTG, and there was no sign of contamination after it re-entered and landed in the Tonga Trench. And that was a extreme outlier due to the high velocity it re-entered at being it was following a trans lunar trajectory.
So justify it. What is the expected number of excess cancer fatalities, given an LNT model, the known activity of NASA RTGs, and the explosion rate of deep space launches?
The people who protest these things expose themselves to orders of magnitude greater risk on their drive to the protest.
Most of the groups who strongly oppose this stuff are against any nuclear material whatsoever entering space. The reasons span beyond basic safety to opposing any combination of space programs with nuclear programs.
There are actually quite a few RTGs on Earth (most of them - IIRC - in remote Soviet-era outposts and such) that I'd be more concerned about; they tend to be in remote areas where maintenance is difficult.
It's a pity you're getting downvoted, I thought it was funny.
On a serious note, presuming a significant increase in trust among all parties, wouldn't this idea radically change an ominous situation (Iran having weapons-grade plutonium laying around) into one with peaceful, mutually beneficial, trust-building cooperation between formerly antagonistic nations? Have not stranger things happened?
I'm skeptical that this small reactor rivaled the Uranium program. If your rush 239Pu production, you end up with a product that is very difficult to purify, raises the probability of a fizzle, and generates thermal problems for the pit.
The needed isotope (Pu-238) is only present in small amounts in used reactor fuel.
The concern with Iran is that they might enrich uranium to the point where it is useful in a nuclear weapon (it is useful in a reactor well before this point).
But wait, you're thinking, fusion reactors based on current technology consume more energy than they can produce. That's true, but also irrelevant if your business model is producing tritium rather than energy. This is because the going rate for tritium (according to Wikipedia) is something like $30,000 per gram [2].
I'm not sure what the licensing requirements are on fusion reactors, but I think they're a lot less onerous than licensing a new fission reactor. I don't think there's any licensing requirement at all for a small fusion reactor like a Farnsworth fusor.
Disclaimer: This is just idle speculation because I haven't done the math.
[1] http://en.wikipedia.org/wiki/Fusion_power#Power_Production
[2] http://en.wikipedia.org/wiki/Tritium#Self-powered_lighting