Talk:Radioisotope thermoelectric generator

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What would happen if a space probe which is powered by these RTG's (I do not totally understand what an RTG is) that are fueled by plutonium crashed into earth?? I suppose it would get burnt up on its entrance into the atmosphere.... but for arguments sake what if it hit a large city like say Tokyo, or LA?

Not much, if it was right before launch; the reactor isn't turned on, IE, the material isn't pushed into criticality until after it's clear of the atmosphere. If it's on a satellite and it crashes, the RTG is a thick casing of metal, designed to survive re-entry intact. The chances of it hitting a populated area are extremely rare, in the first place. It's used on so few satellites anyway, because of the nuclear fuel's extreme rarity. Only big probes like Cassini-Huygens, the Viking program and the Voyager program use RTGs, anyway. Phoenix T'ril
"Not much, if it was right before launch; the reactor isn't turned on, IE, the material isn't pushed into criticality until after it's clear of the atmosphere" - it is NOT a nuclear reactor and no nuclei are fissioned so there's no criticality - the radioisotope just generates heat all the time, you can't switch it off. I think the rest of qhat you said is true; if the thing hits a large city I guess there would be some local contamination which may cause some casualities but could be cleaned up quickly(if we're lucky and it enters the atmosphere at the right angle, the thing might not even break up and land just like a meteorite). 13:36, 5 Jun 2004 (UTC)
The item about RTGs being "live" from birth is correct. This was one of the many difficulties with the Galileo program. When launch of the Galileo probe was postponed after the Challenger disaster, the probe went back into storage for a few years, while the power levels of its RTGs continued to decay. When it was finally launched,the mission plan had to compensate for the reduced power budget. gvgoebel
They are designed to survive reentry and the whole idea on how people get their undies in a bunch is because people are terrified with anything with the word "nuclear" attached to it. RTGs if they blew up would survive reentry and when they hit the ground they most likely wouldnt break (as in break apart) when they hit the ground. If they did break up when they hit the ground EVEN if it was in the middle of a city (which I might add is very unlikely as those areas are like tiny pinpricks in the vast area of nothing) it could be cleaned up quickly. As it is neither like a dirty bomb (having lots of small particles picked up by the air) or a nuclear weapon (no explosion). I don't even think it would be possible to get one to land on a city as NASA takes extra care when launching them so they dont go over highly populated areas, or if they do as few as possible, and only small areas, for the paranoid people out there. Go nuclear power! It by far has the least polution and it is environmentally friendly as well. (Yes I know RTGs aren't nuclear power in the conventional sense, im just making a statement.) Ergzay 21:54, 11 October 2007 (UTC)

RORSAT Reactors[edit]

Hi All:

Nice article, but there's a minor bug in it -- the Soviet US-A RORSATs didn't use RTGs, they actually used full-blown fission reactors, which are a somewhat different breed of animal. See:

-- for details. I have made the appropriate changes. Suprised nobody caught that one. (Also added a bit about use of "plutonium cells" -- micro-RTGs -- in heart pacemakers.) gvgoebel

Thanks for fixing up the RORSAT part of the article. I think I wrote that so its my fault that it wasn't completely truthful. I made some small changes to what you had written to make it sound more 'encylopediac' - like the idiom 'push comes to shove'.--enceladus 22:15, 12 Aug 2004 (UTC)

I have moved the RORSAT section to the RORSAT article. It didn't really have any relevance here. Bobbis 00:38, 27 Oct 2004 (UTC)

Dangers of plute-238[edit]

The following paragraph:

Plutonium-238 is not fissile, so there are no nuclear proliferation risks associated with it - That is to say, it is useless for making nuclear weapons. However it is moderately poisonous and radiotoxic.

which I added was immediately removed by User:Deglr6328, who claims 238 is in fact, fissile.

Pu-238 is fissionable but not fissile. All fissile nuclides have an odd mass number and an even atomic number. The reasons for this were documented as part of the liquid drop model of the nucleus by Bohr and Wheeler and independently by Frenkel. Interested to hear of any source that claims that plute-238 is fissile, have a look at IEER plutonium facts for one that says quite clearly that it isn't. Andrewa 10:33, 18 Jan 2005 (UTC)

I think the problem was that sie misunderstood "fissile" to mean "undergoes fission". I put in something that is clearer (I hope) about the distinction. I think something should go on plutonium to elaborate, possibly including what you just said. --Andrew 20:00, Jan 18, 2005 (UTC)
I'm sorry for not putting something here when I rv'd, as I had to leave. I do think 238 is actually fissionable and fissile! It does indeed have a critical mass of around 10Kg and therefore represents a proliferation threat. [1] --Deglr6328 23:29, 18 Jan 2005 (UTC)
Well, that's certainly authoritative enough on the "fissile" issue. I'm still not sure I agree that it represents a proliferation threat. Forming a critical mass is not sufficient to construct a nuclear weapon; you have to store a subcritical mass, then rapidly assemble it into a prompt critical mass, which must remain together long enough for sufficient fission to occur. For one thing, a 10 kg piece of Pu-238 will emit 500 watts of heat and be highly radioactive, so building a bomb around it will be difficult. Is Pu-238 a greater proliferation risk than natural, unenriched uranium? Critical masses of unenriched uranium are what CANDU reactors run on... --Andrew 02:25, Jan 19, 2005 (UTC) (sorry, I used confusing indentation before; hopefully this will be slightly less confusing --Andrew 05:30, Jan 19, 2005 (UTC))
I'm afraid you are misquoting the paper you cite here, probably unintentionally. Note the word hypothetical which the authors consistently use to describe the critical Pu-238 systems they are investigating. It means that it may not be physically possible to assemble these systems.
The paper uses the word "hypothetical" only thrice, not throughout. And it uses the word "hypothetical" only to stress, that the results in the paper are from computer simulations rather than real experiments. But that doesn't mean, that the reactivity of Pu-238 has not been verified. The paper even quotes experimental data from W. F. Stubbins, D. M. Barton, and F. D. Lonadier, "The Neutron-Production Cross Section of 238Pu in a Fast Spectrum," Nucl. Sci. Eng., 25, 377 (1966): "These experimental data show that the ratio of the reactivity worth of 238Pu/239Pu for bare metal was 0.99 +/- 0.09 (subcritical measurements) and 1.02 +/- 0.09 (critical measurements)." Kai Petzke (talk) 18:50, 29 August 2013 (UTC)
The paper you cite doesn't say either way, but in fact it isn't possible in the case of pure Pu-238, which is part of the reason Pu-238 is not considered fissile. These critical masses exist only as equations and tables. There's no danger of anyone making one. Andrewa 04:18, 19 Jan 2005 (UTC)
I don't think so, actually - the calculations are for (among a variety of other possibilities) a bare metal sphere of Pu-238. (And also a bare metal sphere of Pu-238 and Pu-239 in the proportions likely to be found in an RTG). So, if one had enough, making such a critical mass would be easy (if stupid). Make two hemispheres, slap them together, then fall over dead a few hours later. Powder would probably do fine, although you might need a bit more (they give figures of oxides too, and the loose packing might make life difficult): just fill a bucket; the non-fission heat will quickly sinter it into a solid mass (and probably melt it, with 500 watts). Shortly you will have a critical mass and a very big mess. If you examine the paper, you will see that one of their goals is to determine safe limits on handling of plutonium for RTGs.
I assume you are basing your impossibility claims on the liquid drop model? Keep in mind it's only an approximation to a nasty quantum-mechanical problem. Moreover, the key claim you need is something to do with a neutron capture cross-section (in fact, a triggered fission cross-section) which was one of the inputs to the mathematical models in that paper; they got it from real measurements.
My only remaining concern is about the proliferation concern: is Pu-238 at all useful for building atomic bombs? I think the answer is no. But I have as yet no positive evidence for this; it's worth a second look at a page I saw a while ago on the Integral Fast Reactor: [2]. Some quotes:
And what do you mean by "fissile" and "fertile?"
An isotope is called "fertile" when the addition of a neutron changes it into a fissile isotope - one that, like U-235, has a very high probability of undergoing fission when exposed to thermal neutrons. Both fissile and fertile isotopes are fissionable - it's just that fertile ones require a high-energy neutron to make them split.
In our case, I would say that Pu-238 is fertile, not fissile. In the paper cited earlier, they say the same thing: chain reactions are mediated by fast neutrons.
Later, we have:
Even so, with plutonium of almost any isotopic composition it is technically possible to make an explosive (although designers of military weapons demand plutonium that is at least 94% Pu-239)[...]
He describes "reactor-grade plutonium", which is 60% Pu-239 and 40% Pu-238 and claims that it's hard to build a bomb out of it; the US built one once.
And finally, from the paper cited above:
Mixtures of 238Pu and 239Pu are of interest in preparing heat sources. Generally, such mixtures contain approximately two thirds 238Pu and one-third 239Pu.
Looks like even if Pu-238 isn't suitable for bomb-making, the mixture used in RTGs is, at least potentially.
So I think we have to conclude that the plutonium in RTGs is a proliferation risk, although not a very great one, as it'd probably be necessary to do isotope separation which is just as difficult as isotope separation of uranium. --Andrew 05:30, Jan 19, 2005 (UTC)
I don't understand. Here we have the statement:

"An isotope is called "fertile" when the addition of a neutron changes it into a fissile isotope - one that, like U-235, has a very high probability of undergoing fission when exposed to thermal neutrons. Both fissile and fertile isotopes are fissionable - it's just that fertile ones require a high-energy neutron to make them split." "In our case, I would say that Pu-238 is fertile, not fissile. In the paper cited earlier, they say the same thing: chain reactions are mediated by fast neutrons."

Ok. Now, we want to talk about Pu-238 which, yes, is "fertile" in that if you add a neutron you get the obviously fissile Pu-239. But it is also fissile itself! Take U235, it's fissile with slow (thermalized) neutrons as the guy above says and this is the method of fission induced in a nuclear reactor but is is also fissile by irradiation by FAST ("hot") neutrons, this being the method of fission used in the exceptionally dangerous U-235 bomb. And it's the fast neutron fission in Pu-238 which allows it to be fissile. I mean, how could it possibly have a critical mass if it weren't fissile[3]!? I do agree with you on the proliferation thing though. Pure 238 would release so much heat it would probably melt itself and destroy any lensed conventional explosives around it before it could be detonated. --Deglr6328 07:21, 19 Jan 2005 (UTC)

There seem to be (at least) two definitions of fissile floating around. Helpfully, we include both, each claiming to be the definition. On fissile, we claim it's "capable of undergoing a fission chain reaction". On fissile material, we claim it's "fissionable by slow neutrons". The impression I get is that nobody worries about fast-neutron-based chain reactions, which is odd, since I don't think there's any moderation in a nuclear weapon.
Some googling reveals:
Fissile material
Although sometimes used as a synonym for fissionable material, this term has acquired a more restricted meaning. Namely, any material fissionable by thermal (slow) neutrons. The three primary fissile materials are uranium-233, uranium-235, and plutonium-239.
What are fissile materials?
Fissile materials are composed of atoms that can be split by neutrons in a self-sustaining chain-reaction to release enormous amounts of energy. In nuclear reactors, the fission process is controlled and the energy is harnessed to produce electricity. In nuclear weapons, the fission energy is released all at once to produce a violent explosion. The most important fissile materials for nuclear energy and nuclear weapons are an isotope of plutonium, plutonium-239, and an isotope of uranium, uranium-235. Uranium-235 occurs in nature. For all practical purposes, plutonium-239 does not.
2. Physics Fissionable, especially by neutrons of all energies.
Fissile material
Material composed of atoms that fission when irradiated by slow or "thermal" neutrons. [...]
That question seems to have been resolved by calling the materials, that can support a chain reactions with slow neutrons "fissile", and the materials, that can support a chain reaction with fast neutrons "fissionable". At least another Wikipedia article does so, and it seems a reasonable definition. What I wounder, and have no quote about, is how dangerous criticallity accidents with fissionable (but not fissile!) material are. As no thermal neutrons are involved, such criticallity accidents might as well end up as quite strong explosions, as reactivity is not reduced, as temperature increases, but only, once the material starts to evaporate. Kai Petzke (talk) 18:50, 29 August 2013 (UTC)
So it looks like there's no consensus in how the term is used. But what we need to know is what this article should say. Here are the facts we should verify:
  • Is RTG plutonium pure Pu-238 or a mix of Pu-238 and Pu-239? If pure Pu-238, how is it produced?
  • Pu-238 or a Pu-238/Pu-239 mix can undergo a chain reaction.
  • Pu-238 is not regulated as a fissile material.
  • Pu-238 or a mix generate a great deal of heat (0.557 W/g for Pu-238) so that a mass sufficient to become critical would be pouring out 5 kW, making bomb assembly difficult.
  • The US has conducted a bomb test (with unknown results) with a bomb built from a 238/239 mix.
  • Can RTG plutonium be produced without reprocessing plants that would make production of bomb-quality plutonium easy?
--Andrew 17:18, Jan 19, 2005 (UTC)

I just removed the proliferation claim until we can decide whether it's true or not. Better to say nothing than be wrong. --Andrew 17:22, Jan 19, 2005 (UTC)

While plutonium-238 does undergo spontaneous fission, it is not capable of sustaining a nuclear chain reaction, so there are no nuclear proliferation risks associated with it - that is to say, it is useless for making nuclear weapons. However it is moderately poisonous and radiotoxic.
My question remains. How can something which "is not capable of sustaining a chain reaction" have a critical mass?!--Deglr6328 08:00, 31 Jan 2005 (UTC)
Well, that would be why it's not in the article anymore. It's here because if we can understand to what extent Pu-238 poses a proliferation risk we might want to say something about it. In particular, it mightbe worth mentioning that it's not like we're leaving all this weapons-grade plutonium just lying around. Unfortunately, it seems difficult to find authoritative references on the real proliferation dangers of Pu-238. --Andrew 09:02, Feb 1, 2005 (UTC)

We can safely claim that 238Pu is proliferation-resistant. The major reason is that 238Pu fissions spontaneously and thus emits neutrons randomly. If you want to manufacture a nuclear bomb, you have to bring the plutonium together to its critical mass very fast - this is usually done by surrounding the bomb with conventional explosives and make it implode before initiating the nuclear reaction. The presence of a neutron emitter inside the bomb material will cause the chain reaction to start too early and cause the bomb to fizzle, greatly reducing its reliability and power; this is also why the plutonium produced in commercial nuclear reactors, which contains significant amounts of 240Pu (which aslo fissions spontaneously), is unsuitable for nuclear bombs as I pointed out recently in the plutonium article. Moreover, 238Pu and 240Pu are hot and radioactive, making the bomb manufacturing quite hazardous; and, as discussed earlier, they are not fissile - do not fission with thermal neutrons - and I suspect that the fission cross section with fast neutrons is quite low, thus the critical mass must be large. --Philipum 09:27, 25 May 2005 (UTC)

It is a still strongly believed misconception, that the critical mass of 238Pu is high, or that 238Pu cannot even undergo a chain reaction at all. In fact, 238Pu has a critical mass as low as that of 239Pu! For details see . Furthermore, keep in mind, that due to its shorter half-life and higher decay energy, 1 kg of Pu-238 is as dangerous as 293 kg of Pu-239! In other words, the 19 kg of Pu-238 on Cassini compare to 5.5 metric tons of Pu-239. Nuclear weapon tests combined put an estimated 4 to 10 metric ton of plutonium-239 into the atmosphere. Of course, Nuclear weapon tests combined also released hundreds of kilograms of I-131, Cs-137, Sr-90 and other problematic decay products, which in sum are again more dangerous than the 19 kg of Pu-238 in Cassini, or all the plutonium from the tests. However, if the mid-term (1 week to 100 years after explosion) radiological danger of 19 kg Pu-238 from Cassini is compared to the radiological danger of the decay products of the hiroshima bomb (thus ignoring the neutron and gamma wave of the explosion itself, and the highly active very short-lived decay products), Cassini's RTGs win by far. Keep in mind, that the Hiroshima bomb fissioned around 1 kg of Uranium, which resulted in approx. 20 g Sr-90, 36 g Cs-137, 38 g Xe-135, and so on, that Pu-238 has a very high decay energy and, if incorporated, the alpha radiation has a relative biological effectiveness between 10 and 20 as compared to 1 for the beta and gamma rays from nuclear fallout. Kai Petzke (talk) 18:50, 29 August 2013 (UTC)

Apollo 13 RTG Comment[edit]

Minor comment on the Apollo 13 LM RTG, if anyone's interested: it wasn't part of the Lunar Module, which was battery-powered, but part of a lunar science instrument package that was to be left behind. Of course Apollo 13 never landed on the Moon and the science package was never unloaded from the LM. gvgoebel


The life span section needs to be recalculated using the correct 1/2 life vale of 87.7 y. I'm horrible at math ......--Deglr6328 05:13, 19 Mar 2005 (UTC)

Polonium-210 ever used in space?[edit]

Some site (copies of each other: [4],[5]) says Polonium-210 was used in space but infact another site[6] listing a data sheet on the SNAP geneators says that SNAP-3 though pesented to President Eisenhower in 1960, was never used in a space mission. Instead SNAP-3B was launched which used Plutonium. Until this problem can be resolve with more evidence, I think it is best not to mention any use Polonium-210 of beyond prototype stage Polonium-210. --BerserkerBen 16:32, 19 Mar 2005 (UTC)

After writing an entire damn novel here in response, my friggin browser crashed and I really don't want to rewrite it all. Suffice it to say, there is obviously contradictory information out there (sometimes on the same DOE site!!) on this particular subject and after reading several sites on the subject I suspect you are correct in your assertation that Po never flew as an RTG source. It was in fact Pu, which powered the first RTG and which is variously referred to as a "snap-3" or "snap-3B".
I think I say some sites saying the soviets put a couple in orbit, but details were non-existent.--BerserkerBen 04:20, 20 Mar 2005 (UTC)
One other minor quibble, the bit on bremsstrahlung which originally read "will give off gamma_radiation through bremsstrahlung secondary radiation" and which I changed to "will give off X-rays through bremsstrahlung secondary radiation" and then which was finally changed to "will give off Gammma/X-ray radiation through bremsstrahlung secondary radiation" should I think, not use the term gamma rays to describe the EM radiation given off. While recognizing that the cutoff between x and gamma rays on the EM spectrum is totally arbitrary, the strict definition of each type of radiation is different. Gamma rays, by definiton originate from within the nucleus while X-rays originate from electronic transitions or accelerations.
Yes I'm aware of that but many may see X-rays as more easily blockable, “Gamma rays” more easily describe the energies were talking about,"very high energy x-rays" is to long and requires even longer explanation. Even though its means of creation does not qualify it as a true gamma ray its energy can be equivalent, and that area of the spectrum is a gray in naming.--BerserkerBen 04:20, 20 Mar 2005 (UTC)

Also "210Po; this isotope provides phenomenally huge energy density, but has limited use because of its very short half-life and high penetrating radiation levels." is incorrect. Po210 is a completely pure 5.3 MeV alpha emitter. Shielding is easy.--Deglr6328 22:13, 19 Mar 2005 (UTC)

I would beg to differ: [7] apparently in its production of a alpha ray of 5.3 MeV, about 0.0012% of the time it will produce a Alpha ray at 4.5 MeV and a Gamma ray at .8 MeV. So no it is not a pure alpha emitter, and considering 210Po activity that 0.00122% gamma ray emission is likely very bright.--BerserkerBen 04:20, 20 Mar 2005 (UTC)
Missed that! The gamma activity of 1g Po would then be 2GBq (~54 mCi), not unreasonably massive though. I have to say I still don't like using gamma rays to describe bremsstrahlung. How about we replace the description with "high energy photons"? Also I am confused by the sentance "Even so its shielding requirements in a RTG are second only to plutonium." Does this mean only Pu needs more shielding or only Pu needs less shielding or...? --Deglr6328 05:47, 20 Mar 2005 (UTC)
according this [8] pu238 needs only .1in of lead and Ac-241 needs .7in of lead, if you want to rewrite that to make it sound better please do.--BerserkerBen 07:11, 20 Mar 2005 (UTC) Why not leave it at "gamma/x-ray" it links to x-rays anyways?
Oh alright I guess we can leave it gamma/X-ray. I just like to avoid confusion on the issue whenever possible.--Deglr6328 07:26, 20 Mar 2005 (UTC)

Nuclear Batteries[edit]

Do they have a article of its own? if not making one would likely be a stub, we could mention them here and compare its diffrence from RTGs, then redirect "Nuclear Battery" to that section of this article.--BerserkerBen 03:40, 22 Mar 2005 (UTC)

Yeah I was in the process of making it when I fell asleep at the computer. oops. :) I am calling it "Atomic battery". I don't like this term very much but it is obviously the accepted term in common use [9] to describe a device which derives its power from the collection of electrical charge created by (usu.) beta radiation. It gets something like 3 times the google hits than for "nuclear battery". I don't know what to think of the section in the pdf you linked to about them being basically small RTGs. To be honest I suspect it was conjectural and the author, having previously heard or RTGs assumed this is how the pacemaker did it too. Here is a nice page discussing atomic batteries with a mention of pacemakers[10]. it does not specifically SAY pacemakers are betavoltaic/alphavoltaic devices and not RTGs but it does come BEFORE the section dealing with RTGs. I see other sites which say they were themoelectric too but i rather suspect the generation mechanism must've been more subtle than this. RTGs require substantial thermal gradient to produce any substantial energy output dont they? As I calculate it (heh rather dubious eh...) the pacemakers used 3Ci Pu and with the specific activity of Pu 238 being ~17Ci/g that means they contain about .18g Pu and at a heat emission rate of .39 W/gram the sample inside is emitting only around .07 watts of heat!! I just doubt that such a teeeny heat emission could produce a sufficient thermal gradient INSIDE someone's body to produce useful power levels. Anyway I suspect we will never be able to see an actual detailed diagram of one of these things so we'll never know. In any case, the "atomic battery" thing is now a stub!--Deglr6328 06:12, 22 Mar 2005 (UTC)
Well I don't know, from what I have read "Atomic" batteries produce only nanowatts/microwatts of power, electromechanical Atomic batteries can produce milliwatt pulses every few minutes. At best a atomic battery could be used to trickle charge a normal battery, also atomic batteries have efficiencies between .1-5%. You seem right about a RTG version being rather iffy, but so is a Atomic battery.
Read the new reference. They describe the deisgn and implantation of an in-body RTG; it's definitely thermoelectric. I also found this bibliography whic indicates that people also researched betavoltaic sources ofr pacemakers and Stirling engines for artificial hearts. --Andrew 17:13, Mar 22, 2005 (UTC)

References vs. External links[edit]

It's important to distinguish which external links were actually used as sources and which are simply provided for the reader's edification. I haven't attempted to classify which of the currently listed links were actually used as references, so I just created a new section for external links only. Somebody should go through and sort the links. (This is important both for reliability and for potential Featured Article status). --Andrew 17:09, Mar 22, 2005 (UTC)

All but one link provided information (or a image) that is used in the article, the outlier I moved. I would not like this to become a feature article because of the controversy (scaremongers) that would come to this article. Perhaps we would have to place more information about the safety, concerns and myths-debunks of the 238Pu fuel used first. --BerserkerBen 19:51, 23 Mar 2005 (UTC)

Thank you! I was thinking more of article quality than actual featuring; I agree the article needs more work before it could be featured. I think expanding the controversy section (with specific facts) would be useful. --Andrew 20:26, Mar 23, 2005 (UTC)


Is there a good reason why a scientific article in an international forum is still using imperial units?

Probably because it will have been written using American sources which won't be using metric. Be bold and fix it. Evil MonkeyHello 22:48, 24 August 2005 (UTC)

Need Info on Specific RTGs, Contrast with other Power Sources[edit]

Suggest adding data about physical and electrical characteristics of certain well-known RTGs. E.g, Pioneer 10/11, Voyager 1/2, Galileo and Cassini probes: mass, size, initial and later electrical output.

Suggest also contrasting RTG output/weight/complexity characteristics with competing space power sources such as batteries, solar cells, fuel cells and nuclear reactors. Joema 06:29, 9 December 2005 (UTC)

That is asking for alot, but here is a start: Here is a data table, we can all start filling it. --BerserkerBen 09:20, 9 December 2005 (UTC) Sources [11] [12] [13] [14]

RTG Models
Name & Model Probes Used On

(# of RTGs per probe)

Max Electical


Max Heat


Fuel (Max amount of

Radioisotope used)

SRG in prototype phase, MSL ~110w (2x55w) ~500w ~1kg Pu238 ~27kg
MMRTG in prototype phase, MSL ~110w ~2000w ~4kg Pu238 26-34kg
GPHS-RTG Cassini (3), Galileo (2)

Ulysses (1)

300w 4400w 7.8kg Pu238 55.5kg
MHW-RTG Voyager_1 (3),

Voyager_2 (3)

160w 2400w ~4.5kg Pu238 39kg
SNAP-19 Viking (2), Pioneer_10 (4),

Pioneer_11 (4)

35w 525w ~1kg Pu238 ???
SNAP-27 Apollo 12-17 ALSEP (1) 73w 1480w 3.8kg Pu238 20kg

Thanks so much for providing that info. That is really nice.

Since each vehicle used varying numbers of RTGs, is it possible the table could be expanded to include the # of RTGs per vehicle? Here's the info:

Apollo 12-17: 1 RTG, Pioneer 10/11: 4 RTGs, Viking 1/2: 2 RTGs, Voyager 1/2: 3 RTGs, Galileo - 2 RTGs, Cassini - 3 RTGs Ulysses - 1 RTG

More info: Joema 17:04, 10 December 2005 (UTC)

If you want to add info about pros/cons of RTGs vs other space power sources, figure 7.3.1 of this document has a good chart: Joema 17:10, 10 December 2005 (UTC)

Thanks for the sudjestions but I would be nice if you could tabulate some data as well, its a lot of data I don’t have unlimited time.--BerserkerBen 21:33, 10 December 2005 (UTC)

OK added the info to the table. Hope it's OK, I used the simplest format possible. Joema 22:10, 10 December 2005 (UTC)

Great, a little prettifing to the table and the SNAP-19 weight and I think we can put this first draft up on the page. --BerserkerBen 23:23, 10 December 2005 (UTC)

Below is suggested wording for a new section: Joema 00:52, 11 December 2005 (UTC)

It seems that the table contains wrong data, at least for the mass of Pu fuel in the RTG used for the Cassini mission craft : mentions 72 lbs (~33 kg) total (meaning 11 kg per RTG), as well as the Wikipedia page about the Cassini mission. But maybe I did not understand the meaning of this mass ? Jpetazzo 9:19, 6 November 2009 (UTC)

RTGs vs Other Space Power Sources[edit]

RTGs are evaluated against other power sources and selected whenever their characteristics best fit the application. Alternatives include batteries, fuel cells, solar arrays, and nuclear reactors.

Prime characteristics to consider are mass, mission duration, distance from sun, and load power. Load power is the power drain in watts at any point in time. In general RTGs are most useful for long duration missions far from the sun where load power is modest. Solar arrays are useful for longer duration missions closer to the sun. Fuel cells are used for moderate duration missions where mass or high load power precludes solar arrays. Batteries are used on short duration missions where load power is modest. Nuclear reactors are considered farther from the sun when both high power and long duration are needed.

Another key issue when evaluating space power sources is energy density in watt hours per kg and power density in watts per kg. Because of weight limitations, space power applications favor the best possible energy and power densities.

Power sources for some well known space vehicles

  • The Hubble Space Telescope solar arrays produce 4,500 watts each and weigh 162 kg each, for a power density of 27 watts per kg.
  • The Space Shuttle fuel cells produce 12,000 watts each and weigh 118 kg each, for a power density of 101 watts per kg.
  • The Cassini and Galileo probes use RTGs, each producing 300 watts and weighing 56 kg, for a power density of 5 watts per kg.
  • The Apollo Lunar Module used batteries weighing 358kg total, producing 65,760 watt hours, for an energy density 183 watt hours per kg.
  • Jupiter Icy Moons Orbiter planned on using an approximately 100 kilowatt nuclear reactor. Mass is unknown. The mission has currently been delayed for reasons unrelated to the power source.

I don't know if we should go into that kind of detial, might be better to have that kind of information on the Space_probes article which is at present nothing but a miniturized List_of_planetary_probes. I think all that is needed for RTGs is to state that they are most desirable power source for space probes needing a few hundred watts or less of power for years on end, in places were solar cells are not viable. --BerserkerBen 19:00, 11 December 2005 (UTC)

If you want to leave out the list of familiar vehicles and their power sources, that's OK.
However a common question readers will have is why are RTGs used vs other power sources. Almost everybody has heard about fuel cells -- those were mentioned in detail in the movie Apollo 13, along with batteries. Likewise everybody knows about solar panels. I think one or two brief paragraphs something like the above would answer the obvious questions without being too detailed. Joema 17:54, 12 December 2005 (UTC)
I think the statement "RTG are most desirable power source for space probes needing a few hundred watts or less of power for years on end, in places were solar cells are not viable." would cover that, we could add in: "RTG are most desirable power source for space probes needing a few hundred watts or less of power for mission durations to long for fuel cells or batteries to provide, and in places were solar cells are not viable." --BerserkerBen 22:02, 12 December 2005 (UTC)
That's fine. Joema 04:37, 13 December 2005 (UTC)

Power output/efficiency issue[edit]

I think it would be worth pointing out that the rate of radioactive decay and thus heat output is independent of the actual electrical power output. This means that an idle RTG, or one that drives a load at a fraction of the maximum possible load, will suffer an efficiency penalty that is large compared with, say, a typical engine/generator set, which can at least vary its rate of fuel consumption to match the load.

If the above is true for an RTG that has been 'activated', as described somewhere above, I think it should be pointed out in the article. An appropriate section could underline the above problems and then go on to point out that this disadvantage is negated in cases where the required load is nearly-constant, thus avoiding periods where the RTG is idle. A good example of a civil installation where an RTG may be practical is in powering runway landing lights; compare this with, say, a UPS backup system that may be operational for 1% of the time.--ChrisJMoor 02:05, 15 December 2005 (UTC)

Could it be simplified by saying something like: "Because a RTG can not be throttled or deactivated it is always producing power, even when not needed, this can be considered a waste of energy and some RTG uses have been to trickle charge a battery so that a smaller RTG is used rather then a larger one to provide maximum power needs al all time... " I don't know something like that we can elaborate. --BerserkerBen 15:58, 15 December 2005 (UTC)

I think something like Ben's description is OK.
Two issues with describing RTG efficiency vs other sources as above: (1) RTGs are typically only used in applications where nothing else is available, so in that sense it's almost academic (2) It's unusual to use term "efficiency" that way for radioactive energy sources. For example:
An intrinsic RTG characteristic is it can't be turned off, but that's normally not described as inefficient. It's like a luminous tritium watch dial -- always on. Do we describe tritium dials as inefficient relative to a battery-powered watch lights that only activate when a button is pressed? No.
To describe it as an "efficiency penalty", and "problems" seems inconsistent with the basic nature of RTGs and the normal use of those terms in engineering. Not saying it's wrong, just an unusual and possibly confusing use of that term vs normal convention.
By contrast, discussions about RTG efficiency usually involve thermocouple conversion efficiency. That is a true efficiency issue, since it takes a lot of heat to produce a little electrical power, and available materials limit the sustainable heat. That's also why Stirling RTGs are under investigation, because they can triple efficiency. Note how the term efficiency is used in this case: the amount of electrical power out vs thermal power in.
It's true RTGs must either be sized for the maximum projected load or peak load must be provided by batteries. Joema 20:30, 19 December 2005 (UTC)

Good stuff, Joema. You are of course right. But part-load operation is empirically an efficiency issue if the generator is used in a system with variable or, perhaps more accurately, unpredictable load. (But its not usually applied under those conditions, right?) Hows about some mention that the decay process cant be throttled or turned off and a discussion of the most appropriate/least appropriate applications given this limitation?

Is there any future for RTGs as generators and heat sources for more widespread, civil applications such as my aforementioned runway lights? They are 'non polluting', after all. What would be the cost of the power (electric or heat) compared with fossil fuels and wind generators, etc. I am asking this because I actually searched for the page originally while looking into independent/decentralised power systems.--ChrisJMoor 02:51, 20 December 2005 (UTC)

Well, with Pu238 costing $1400+ per gram I don't see any other economical use for RTGs other then space probe. I also think many of the things you asked for Chris is already in the article. --BerserkerBen 03:20, 20 December 2005 (UTC)

Chris, it's true while not usually described that way, the part-load issue is a type of efficiency consideration. However RTGs are generally only used when nothing else will work, so in that regard it's a moot point. Re fossil fuels, wind, etc. see my comments in this article: Joema 00:30, 23 December 2005 (UTC) [| Hydrogen vs. Fuel Cells vs Wind Power]
As for above comment, Pu-238 is not currently mass manufactured and there are cheaper isotopes (ie. Sr-90). RTGs are already used in some lighthouses, underwater probes, pacemakers etc. and could see wider application in the future. 01:29, 30 October 2006 (UTC)

Safety section[edit]

This section seems mostly OK. However there's been tremendous concern and confusion over potential plutonium release from RTG accidents. I wonder if a couple of sentences to help readers put the risk in perspective would be worthwhile. Not sure how to word it, but a couple of items:

There have been over 1,000 atmospheric nuclear bomb tests, which released over FOUR TONS of plutonium 239 into the atmosphere. By contrast the plutonium in RTGs is encapsulated and designed to prevent release.

Plutonium is lethal if inhaled in dust form, even in tiny quantities. However it isn't chemically toxic, and can be safely held in your bare hand. In fact the plutonium core of the first atom bomb was hand assembled. Even in the event of an RTG accident, the plutonium material itself isn't immediately of severe danger unless it was somehow made into dust and inhaled. The plutonium in RTGs is in ceramic form which makes atmospheric release less likely, even during an accident.

If any physicists reading this know otherwise, please say so. Joema 05:00, 3 January 2006 (UTC)

It is important to note that the Pu pit in the Trinity device was encapsulated by electroplating with Ni . --Deglr6328 07:36, 3 January 2006 (UTC)
Ah, that's a good point. There was a very thin layer of Ni electroplated on. However my main point is even pure weapons-grade Pu239 isn't as dangerous as most people think. The beta and gamma emissions are so low it's no significant problem even for people holding a chunk in their hand. Alpha emissions are mainly a problem if you inhale Pu dust or eat it.
Here's a picture of someone holding a chunk of pure plutonium using rubber gloves. Obviously radiation isn't an issue in this case. [[15]]
If a reentering RTG landed in my back yard, I wouldn't walk over there until it was cleaned up, just as a precaution. But it's not like Chernobyl. Since several TONS of Pu239 have been spread into the environment via weapons tests, it's obvious the encapsulated ceramic Plutonium from an RTG is by comparison relatively little hazard, even in the rare cause of an accident. This is so widely misunderstood, it seems the safety section of this article could objectively include some small aspect of this, so readers would go away with the correct factual impression. Joema 20:21, 3 January 2006 (UTC)
Please go right ahead and do it! Some things though try to ne neutral, for example say: "Some have argued that since 4ton+ of Pu239 have been released into hte atmosphere by nuclear weapons... " that kind of thing, we don't want to get the anti-nuclear nuts mad. --BerserkerBen 22:29, 3 January 2006 (UTC)
I made the changes. Tried to keep it minimal, objective, and purely factual. Didn't say "some have argued", just stated the fact and let people draw their own conclusions. If you can possibly avoid saying "some have said...", etc I think it's better. Also tweaked the preceding paragraph to add aeroshell descripton, and added a link to a DOE RTG document.
Its all good, as long as it does not openly attack the nuts.--BerserkerBen 06:36, 4 January 2006 (UTC)

A question. In the part about the Cassini probe, the probability of an incident occuring is calculated at 1/1400 + 1/476 + 1/1000000 = 0.2% . A bit further down, we read there have been 28 incident-free RTG missions, and 4 missions with known incidents. This is a measured probability of 4/32 = 12.5%. Even taking into account we're only doing a rough calculation, the difference between calculated and observed probability is large. — Preceding unsigned comment added by (talk) 09:56, 6 August 2012 (UTC)

Helium Accumulation[edit]

It is known that plutonium 238 degrades by alpha emission. Then, the alpha particles slow down, gain electrons, and form helium gas. Do the pressures created by the helium gas in the small internal space of an RTG ever create problems in the RTG? Polonium 00:50, 18 January 2006 (UTC)

Most RTG design diagrams seem to show a gas relief valve, I guess that is where the helium escapes… hum I wonder if that could have been a contributor to that anomaly on how Pioneer 10 was going off course? --BerserkerBen 02:10, 18 January 2006 (UTC)

I don't think that's completely true. RTGs produce power primarily by fast-neutron-induced fission, just like a bomb. The mass of U238 is well under the critical mass, so there is no "chain reaction" as in a bomb, but an RTG produces power for only about 30 years. U238 has a halflife of over 4 billion years. If you are waiting to get power out of uranium by alpha decay, you are going to wait an awfully long time. Danwoodard (talk) 20:26, 10 March 2014 (UTC)

I'm no expert, but the article says the contrary: RTGs produce energy mostly by alpha or beta decay. And obviously they do not use use U-238, which is too slow to disintegrate, but rather Pu-238, which has a half-life of 87.74 yr. —Edgar.bonet (talk) 19:46, 11 March 2014 (UTC)


A lighthouse needs more that 10 watts of electricity. How can a lighthose RTG wave an electrical power output of 10 watts (they do not use hundreds of RTGs)? 19:28, 25 February 2006 (UTC)

You can check it for your self: There are also bigger RTGs the Russians used, also when they say "lighthouse" they could mean navigational beacons which don't need much more power then a walky-talky --BerserkerBen 20:04, 25 February 2006 (UTC)


As of 2006-04-27: The text "A kilogram of pure 210Po in the form of a cube would be about 95 mm on a side and emit about 63.5 kilowatts of heat (about 140 W/g)" seems wrong. In the Po page it says density = 9.35g/cm3 -> 47 mm cube. 140W/g gives 140 kilowatts/kilogram. Or?? —Preceding unsigned comment added by (talkcontribs)


The safety section of the article seems somewhat POV. For example I have just replaced the paragraph that reads Several tons of plutonium-239 have been released into the atmosphere by over 2,000 nuclear weapon tests. The plutonium-238 used by RTGs is designed to prevent release under the worst possible scenario. It seems to be full of platitudes like this - comparing Pu-238 with Pu-239 is not really reasonable since Pu-238 is radiologically a more dangerous material–ingesting a quantity of Pu-238 would give you nearly 300 times the alpha radiation dose of ingesting the same amount of Pu-239. And the main reason that atmospheric testing was stopped was because of the amount of radioactive material released into the atmosphere. And what is the "worst possible scenario", how about an RTG falling into the hands of terrorists, the fuel removed, ground into dust and used in a radiological weapon. Unlikely, but possible. I suspect that this doesn't happen because of the efforts of security and law enforcement people rather than anything to do with the design of the device.

The section also only addresses spacecraft RTGs, which must be the safest type, since there aren't many of them, no expense is spared in designing, building and looking after them, and unless something goes very badly wrong indeed spend their working life in space. But not a word about those rotting ex-Soviet RTGs shown in the picture. Surely that type of RTG must represent a far bigger danger. Jll 10:29, 22 June 2006 (UTC)

Shot in the Chest?[edit]

"They pose a hazard if the wearer is shot in the chest with a gun."- Just thought i'd point this out... I think getting shot in the chest with a gun has many disadvantages even to those of us without radioactive pacemakers.

I think it meant to other people. like paramedics who'd be unaware of the hazard.--Deglr6328 03:46, 9 October 2006 (UTC)

No, I think someone is having fun "They pose a hazard if the wearer is shot in the chest with a gun. The wearer could suffer injury and even death in the case of a gunshot wound to the chest. Multiple stab wounds in the chest may also shorten the life expectency of 238Pu-powered RTG users." I laughed until I cried a little - fun! Non-encyclopedic (or unencyclopedic but hilarious nontheless. —Preceding unsigned comment added by Jonathan888 (talkcontribs) 23:12, 2 October 2007 (UTC)

The article still states "They [plutonium cells] pose a hazard if the wearer is shot in the chest with a gun." A hazard to others? Lavenderbunny 21:50, 4 October 2007 (UTC)

Radiation Output[edit]

Why doesn't the article mention normal radiation output let's say at 1 meter from the RTG surface when in normal operation? At least for a few RTG types. I haven't found any references for that information, but presumably someone has them. I bet that's far more a concern for those involved in spacecraft assembly than any remotly possible catastrophic launch accident. —Preceding unsigned comment added by Rnbc (talkcontribs) 15:24, 3 September 2007 (UTC)

I don't have a numeric answer for you. But RTGs are typically fuelled by Pu-238, whose primary radiation output is alpha rays. They will totally dissipate after passing through a few centimetres of air (alpha decay), and apparently cannot penetrate human skin; elsewhere in this page it's written that Pu-238 would be safe to hold in your bare hands, except that in large quantities its high temperature might burn you. The story changes dramatically if you inhale or ingest Pu-238 particles, at which point the alpha rays would be in a position to do much more harm. 12:48, 20 September 2007 (UTC)
The decay chain produces gamma emmiters, and since Pu238 decays rather quickly than becomes a problem even after a few months. I've seen values as high as 100rad/year quoted for Pu238-powered pacemakers (ok, at 2cm from the shell, mind you, but then they also don't contain many kilograms of Pu238). Rnbc 11:43, 18 October 2007 (UTC)

I believe the gamma emitters are fission daughters, not decay products. The halflife of U238 is over 4 billion years, so not much is going to accumulate in terms of actual U238 decay products.Danwoodard (talk) 20:30, 10 March 2014 (UTC)

New Ref[edit]

  • Tibor S. Balint, James F. Jordan (2007). "RPS (Radioisotope Power Systems) strategies to enable NASA's next decade robotic Mars missions". Acta Astronautica. 60 (12). doi:10.1016/j.actaastro.2006.12.003.  Text "pages 992-1001

" ignored (help) --Stone 10:15, 30 April 2007 (UTC)

Baldly writen section, and unsure of correct information.[edit]

This is from the fuels section:

  • For spaceflight use, the fuel must produce a large amount of energy per mass and volume (density). Density and weight are not as important for terrestrial use, unless there are size restrictions.

This is badly written. It first states that mass and volume are important then in the next sentatnce it says that density (mass and volume) and wieght (basically mass) are not important unless there are size restrictions (volume and/or mass).

Now mass is probably very important, what's stopping me from editing this is because I'm not familar with the typical cargo hold size for most rockets or space shuttles. Could be most of the time they have some space to spare since they try to slim back so much on the mass. (talk) 12:30, 31 December 2007 (UTC)

Non-stop voyage[edit]

Are non-stop voyages real? I just read about Voyager 1 launched in 1977, still alive and kicking now some 10 billion miles away from earth, without power replacement. So, who needs oil? Anwar (talk) 18:42, 3 May 2008 (UTC)

"Most RTGs use 238Pu which decays with a half-life of 87.7 years. RTGs using this material will therefore lose 0.51 / 87.7 or 0.787% of their capacity per year. 23 years after production, such an RTG would produce at 0.523 / 87.7 or 83.4% of its starting capacity. Thus, with a starting capacity of 470 W, after 23 years it would have a capacity of 0.834 * 470 W = 392 W. However, the bi-metallic thermocouples used to convert thermal energy into electrical energy degrade as well; at the beginning of 2001, the power generated by the Voyager RTGs had dropped to 315 W for Voyager 1 and to 319 W for Voyager 2. Therefore in early 2001, the thermocouples were working at about 80% of their original capacity." (from the article page). So, yes the Voyagers are on *real* non-stop voyages still being powered well and will continue to be so for a good while yet to come ;>)Pomona17 (talk) 11:34, 2 August 2008 (UTC)

U.S. RTG's[edit]

I added two models manufactured by Teledyne Isotopes and used by USAF. I didn't have time to glean more info from the cited open-source document, but I bet someone could! I am surprised at the nearly complete lack of reference to US-built units. Please add more to this article if you can find the info! Highspeed (talk) 05:18, 19 January 2009 (UTC)

Sr-90 power density[edit]

The article says: "this isotope [Sr-90] has [..] much lower energy density". In fact Sr-90 has twice the power of Pu-238, most of which is from Y-90 decay. If weight is meant to include shielding etc, the power density may actually be lower for strontium RTGs, but NOT for the isotope itself. —Preceding unsigned comment added by (talk) 11:16, 22 February 2010 (UTC)

CIA`s Lost Himalayan RTG[edit]

In 1964 the CIA wanted to evasdrop on the Chinese testsite at Lop Nor in central Asia. Together with the Indian Intelligence Bureau (IB) they intended to place a RTG powered radio relais station in fall 1965 at the top of Nanda Devi (25.5 kft) in the Himalayan mountains. Unable to do the mission before winter they decided to secure the refrigerator sized device to a rocky outcropping and return for it next year. In spring 1966 they discovered that it had been swept off the mountain by an avalanche.

Several expeditions were unable to locate the RTG again. Today the RTG is still believed several thousend feet below at the ground of an immense glacier the feeds the Ganges river. Another station placed on Nanda Kot (22.5 kft) operated several month until its antennas were covered in snow. This RTG, still at place, melted for itself under the snow a glistening cavern five feet across. This station was recovered.

It is belived that the missing RTG melted itself to the ground of the glacier and keeps its own cave for some centuries. An Indian goverment report concluded that, once crushed, the 4 pound plutonium would be enough diluted to not pose a serious health risk for the many people who drink from the river Ganges.

The story was first broken by Howard Kohn in an article entitled "The Nanda Devi Caper" in Outside magazine in 1978. Captain Manmohan Singh Kohli, the IB officer in charge of the project published his account in 2002: Spies in the Himalayas - secret missions and perilous climbs, University Press of Kansas. The latest book and first with extensive accounts from the American mountaineers is by Pete Takeda: An Eye on Top of the World, Thunder's Mouth Press, New York, 2006.

With Takeda`s book and declassified documents from the Los Alamos National Laboratory a new fact about RTGs was discovered. The Pu 238 RTGs, partly by impurities, partly by alpha-neutron reaction, emitted considerable neutron radiation. Neither the American mountaineers nor the Indians were briefed on this danger for people close to the RTG. One of the Americans sees a link to his cancer.

On the legendary CIA mission and the recently revealed neutron radiation of RTGs: Peter Lee: Did A Plutonium Generator End Up in the Ganges?, CounterPunch, June 30, 2008 (On the Web).

-- Carel A. Kraft (talk) 17:12, 7 March 2010 (UTC)


I've moderated the language. A shortage of plutonium for space probes is not a crisis. A crisis is something that creates grieving widows, or starving children, or at least causes some sleepless nights to more than a few grad students working on dissertation topics. The NPR article doesn't even quote any of the boffins involved as using the word "crisis". --Wtshymanski (talk) 14:53, 2 November 2010 (UTC)

And one might imagine that a lack of poisonous radiactive waste from atom bomb manufacture, no longer available for some to strap to a rocket that may blow up and disperse it through the atmosphere, is the very *opposite* of a crisis. --Wtshymanski (talk) 15:20, 2 November 2010 (UTC)
I could protest many of your points, but I'm not sure what the purpose would be. I have changed "crisis" to "shortage" and I hope it will end at that. --BlueMoonlet (t/c) 18:18, 2 November 2010 (UTC)
I don't think the proposed language is very neutral; "shortage" almost implies there's some desirable non-zero level of production and use of plutonium to be bolted onto rockets. Could you rephrase this in some what that doesn't imply American taxpayers should be asked to pay to make a toxic metal that other taxpayers may have to pay to clean up? --Wtshymanski (talk) 18:27, 2 November 2010 (UTC)
"Shortage" means that the supply cannot meet the demand. It does not imply any approval of the demand, but just notes that it exists.
Incidentally, the safety standards for space-borne RTGs (without which exploration of the outer solar system is practically impossible) are exceedingly high, meant to ensure containment even in case of a launch failure. Click here for more info (and yes, I know the conspiracy theory they lead with doesn't apply to you, but useful info is further down in the article). --BlueMoonlet (t/c) 17:06, 3 November 2010 (UTC)
<outdent> The article does mention the safety concerns about use of RTGs. --Wtshymanski (talk) 18:02, 3 November 2010 (UTC)

"Could you rephrase this in some what that doesn't imply American taxpayers should be asked to pay to make a toxic metal that other taxpayers may have to pay to clean up?" - We can play this game with just about everything.--Craigboy (talk) 23:47, 29 December 2010 (UTC)

Safety record/edit[edit]

The list is about accident involving RTG powered spacecraft, but are also listed RORSAT satellite that didn't used it (as stated in the period). Is there any reason to keep them in the list? (talk) 10:07, 9 January 2012 (UTC)

No. Removing it. Kolbasz (talk) 18:27, 2 April 2013 (UTC)

Diagram shows no thermocouples[edit]

Thermocouples and heat source/sink are the essential components. This image shows thermocouples, but I don't know its licence: — Preceding unsigned comment added by Darsie42 (talkcontribs) 08:41, 6 May 2013 (UTC)

If you're referring to this one:
Diagram of an RTG used on the Cassini probe
Then it's the "Silicon-Germanium (Si-Ge) Unicouple". The article could do with a cleaner diagram than that one though. Kolbasz (talk) 10:18, 6 May 2013 (UTC)

SRG issues[edit]

I don't see any sources backing up the substantial claims made by the Stirling Radioisotope Generator. Where is this information come from? I've been following SRG development and I'm skeptical of "experimental results demonstrate that an SRG could continue running for decades without maintenance." As far as I know, current SRG development's primary issue right now, and why it hasn't replaced RTG's decades ago,is due to reliability and lack of positive experimental results.

Since I can't back up these claims with literature, than I can't add it. At the same time, the positive claims made (or even its existence) should not be added unless sources support it. In my humble opinion, the whole SRG reads like an advertisement written by people working on the project. — Preceding unsigned comment added by T59Man (talkcontribs) 17:28, 7 November 2013 (UTC)

Great source on RTGs[edit] --Craigboy (talk) 09:33, 25 April 2014 (UTC)

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