Nuclear Propulsion - The best way for space travel

soph · 2003-03-16 08:37:28

Water is a good radiation shield. So is lead. You could include several layers of radiation protection, like you would for the crew anyway. But I don't think solar radiation would be that much of a problem.

Josh Cryer · 2003-03-16 08:45:34

Maybe we wouldn't need it, since the field would be so strong, but you never know. We have yet to actually build a reactor outside the confines of earth's magnetosphere.

Lead is prohibitively heavy, I would think. And using water as a sheild may be silly, since it'd run out eventually (we're using it for fuel, right?). I think a good solution is some sort of passive shielding. Just run a rod through the ship and shoot some current in it. That fusion reactor would give you more than enough energy to have a very large magnetic field surrounding the whole ship.

soph · 2003-03-16 09:16:38

You could use the water that the ship will need for its crew. Keep the pipes filled with it, in a constant cycle. I don't think this water would be unsafe-water is a very stable molecule.

Lead was just an example. There are other materials that shield radiation well, and could serve as part of the ships hull.

Preston · 2003-03-16 11:47:27

Solar wind and external fields (ie near Jupiter) are not a problem, the field of the reactor is ridiculously stronger (on the order of 10 T) and if necessary tiny adjustments would be made automatically.

Josh Cryer · 2003-03-16 12:48:12

Yeah, I figured the magnetic field would be many orders of magnitudes stronger, so it was a silly suggestion, really. The only issue might be solar radiation affecting components, or fluctuations or whatever, and even then, those could be easily foreseen and adapted to.

And yeah, soph, cycling crew water makes perfect sense. How much water does one need, though? Any numbers on how strong water is as a shield depending on how thick it is, etc?

Oh, and to respond to something you said earlier, which I overlooked... I don't think you showed that nuclear outweighs M2P2.

On the fuel acquisition level, they're fairly equal, a fusion drive with water is no harder to find fuel for than a Plasma Sail which uses helium. Although water may be more valuable since it's important for life- helium has no such distinction. But anyway I say this because being able to find a fuel easily is very important, in my opinion.

On the safety level, Plasma Sails win out, hands down. They protect the individuals from outside radiation, and the components are quite easy to make, repair, and just generally deal with. You could probably lug along replacement engines (yes, I said engines, not engine parts, whole freaking engines) if you wanted to. Plasma Sails aren't complex, so you have less systems that could fail and cause the whole thing to stop functioning. Fusion is not so lucky, you necessarily require many redundant systems, otherwise you're sitting on the itchy pinky finger of god. The complexity of fusion vs. Plasma Sails deserves it's own category, even.

On the complexity level, you have Plasma Sails which are made of only a few dozen parts (the final design will probably have more parts to it than the current theoretical design- right now there are less than a dozen individual parts). Fusion reactors, no matter what people want to say, are going to need at least two redundent systems, and are made of many many components. I recall reading that they need to be highly calibrated, too, so I'm skeptical if you could make one out of spare parts, or even repair one that was damaged somehow. Fusion drives would probably need a fission reactor to maintain all the critical systems. Plasma Sail vehicles may incorporate fission reactors, of course, for larger ships or long duration ships or what have you (you can use a sufficiently large enough Plasma Sail to leave the solar system, getting up to half the speed of light or more), but fission isn't as necessary as it is for fusion drives.

On the maneuverability level, fusion obviously wins out. You don't have the same kinds of thrust with Plasma Sails (though with a very large one you could have thousands of newtons of thrust, theoretically). But it seems the pluses for Plasma Sails outweigh the on real problem factor, really. The only things that remains to be seen is whether or not they could work. I'm quite confident.

I expect Plasma Sails to be very cheap ferrys in the inner solar system (sunlight is plentiful there and this is just a no-brainer, really). And I expect them to also be the main drive for extrasolar vehicles (you don't need a lot of maneuverability when you aim for something light years away, you need a very high ISP and lots of thrust; a very large Plasma Sail can provide both).

soph · 2003-03-16 14:00:08

Fusion beats plasma in:

1) Power

2) Thrust

3) Manuverability

4) Payload

How does plasma obviously win out in safety? As preston said, fusion simply dissipates. Van Allen Belts, which can fluctuate, are more of an issue.

Power is very important-say you want a science or mining outpost. All that power (especially for an outpost, which once parked, can switch the engines to straight power reactors) is very useful for high power needs.

Payload, fusion can launch more from the surface, and can be made to be redundant more easily than plasma sails. Complexity? Besides the heat, there are three basic components for fusion. A magnetic field, microwaves, and the reactor chamber.

Now you are just latching on to this fission for fusion idea. That's assuming we can never get a net power gain out of fusion, which is pretty silly. Like I suggested before, we could have redundant systems (which is a no-brainer) and start the engine using an external source. The fusion could then maintain itself. You could even have another fusion reactor on board dedicated only to powering the ship and engines.

Extrasolar? I highly doubt that plasma can beat 13% lightspeed.

Do we know that plasma sails wouldn't have an affect on planetary communcations? What if our magnetic field hit our satellites?

clark · 2003-04-23 09:18:23

http://www.space.com/businesstechnology … 30423.html

Prometheus: Lighting NASA's Nuclear Fire
By Leonard David

NASA?s Project Prometheus is targeted at developing two types of nuclear-powered technologies: Radioisotope-based generators and nuclear fission-based systems.
On the one hand, radioisotope power work falls into two camps, a Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) and the Stirling Radioisotope Generator (SRG). This hardware is expected to greatly improve on those nuclear power packs used to energize such classic space probes as Pioneer, Voyager, Viking Mars landers, and the Cassini spacecraft now en route to Saturn. This technology would enable "all weather, anywhere, anytime" exploration of planetary surfaces.
But the major poster child for Prometheus is the Jupiter Icy Moons Orbiter, or simply known as JIMO in acronym officialdom.
Prometheus calls for fission power reactor research, advanced heat-to-power conversion hardware, as well as power management and distribution equipment.
Mastery of this technology is embodied in JIMO -- a mission with a wished-for launch in 2011, at the earliest. The spacecraft would orbit three different moons of Jupiter where earlier spacecraft discovered evidence for vast saltwater oceans hidden beneath icy surface layers: Europa, Ganymede and Callisto.

Josh Cryer · 2003-05-07 17:27:26

This question is a double sided question, really. It's really directed to the Nuclear Space people, and it may even be somewhat off the topic, because it is more related to energy than anything else.

I was reading one of my old Scientific Americans the other day and came across an interesting statistic; that nuclear energy research and development surpassed all other forms of energy by a huge factor. At first I thought this was just a blurb by an environmentalist (the author of the article I'd read is a self-admitted ecofriendly person), but then I went to the IEA site today and found that this is largely true.

Every year for the last three decades or so, nuclear RD&D has had several times as much money put into it, with, as far as I can tell, very little results.

Why is this? And can we expect this trend to continue? I should note that energy R&D basically peaked in 1980, but this is for all fields, except solar- which has only recently (in the late 90's) made any headway against other forms of energy (still quite dwarfed by nuclear R&D, though).

Is nuclear R&D destined to just be a blackhole where people throw their money without many big results? With all the R&D that you see going into nuclear (for the past three decades), why isn't everyone using nuclear for everything? (I know the answer to this, really, I'm just asking what you think.)

soph · 2003-05-09 20:03:29

Well, first of all, the entire nuclear industry was forced to change its entire approach to energy production when Jimmy Carter outlawed breeder reactors. So a lot of money had to go into developing new energy production systems and retrofitting the reactors.

Another issue is where that R&D money is going. Nuclear research could be going to fusion, which has greater potential than any form of energy production, if it succeeds (which it appears it will by 2015-2020). A lot of money is also being spent on new ideas, such as thorium reactors.

A limiting factor is the vehement anti-nuclear laws. Nuclear research isn't really a black hole. If anti-nuclear laws were relaxed, our fossil fuel industry would be hit hard, which is probably part of the reason these laws exist to begin with.

Josh Cryer · 2003-05-09 21:37:25

Oh, well, I certainly understand why actual nuclear reactor development wasn't carried out in the US, that's not what I'm asking. First, this question is about world nuclear R&D, not just the US. Second, even if it was about the US, the IEA numbers include breeder reactor research (it's all broken down, just go to the site), so the idea that ?development has changed directions? is shortsighted. The charts I were reading are quite broken down, including fusion and fission, so it's clear where the money is going (both fusion and fission take about the same ammount of R&D- the IEA site isn't loading at the momment for me, though, so I can't give you a direct link or numbers!). I doubt thorium reactor research or other alternative reactor designs are responsible for this huge discrespency between nuclear and other energy provider designs.

I agree that the nuclear industry, if allowed to exist, could be a potential fossil fuel killer (at least in cities; smaller urban areas are much more questionable, since they don't really require nuclear reactors and it would just be overkill), but that's not what I'm asking here.

Where is the unlimited cheap energy? We've done the research for the past 30 years...

soph · 2003-05-10 06:14:06

The calculations are quite clear. If it wasn't so restrictive to build a plant, and breeder reactors were used, we would have the boundless energy. 3.2 kg a day of uranium for a 1,000 MW reactor. And, with breeder reactors, you don't have to mine as much, because they create fuel. There's a French reactor that creates enough fuel after 10 years to fuel itself and another reactor for another 10 years (without using an additional plutonium supply)!

Disposal is a huge, and wasteful cost. We could be using breeders to recycle fuel, instead of spending exorbitant amounts to dispose of it.

Josh Cryer · 2003-05-10 12:39:57

Yes soph. Praise to breeder reactors. Amen and amen. That's not my question, however. Heck, it only raises more questions, since they have so much potential, why don't I see anyone lobbying for them to be built not only in the US, but all over the world, also? Does the ban preclude outside nations who have nuclear reactors from building them, or is it just that they are so friggin expensive to build, no one cares for them (if they costs a couple of billion to build, and to be comeptitive with the fossil industry have to sell energy at a cheaper rate, then it could take a long time before profits are being made)?

Man, I wish the IEA site could load, I'd throw the numbers about, right friggin now. I don't see any evidence that nuclear energy is going to suddenly magically start existing all over the place.

soph · 2003-05-10 15:03:33

India has breeders, France has breeders, and that North Korean reactor that we've heard so much about is a breeder.

People have been lobbying for them in the US and abroad, but the anti-nuclear and fossil fuel lobbies are either too strong, politically connected, or fear-inspiring to be broken.

And in addition, a smaller nuclear plant could provide more energy to a greater area than fossil fuel plants, so the vastly smaller amount of fuel needed, as well as the increased customer base would probably allow competitive rates.

Josh Cryer · 2003-05-10 17:53:18

Okay, the IEA site is loading now.

First, so that you can see what I'm talking about with respect to nuclear R&D, go here. You're going to have to browse to the particular area, because I don't think I can get a direct link to the applicable page.

Click on RD&D Budgets, then expand the Rows to 50 and Columns to 25. Scroll down to the nuclear section, it's fairly straightforward. See how nuclear surpasses basically all other forms by an order of magnitude? It's actually quite ridiculous, when you look at it. I should actually point out that breeder research did slow down in the mid to late 80s, but nuclear R&D was and is still quite strong...

You suggested that, at least on the surface, there is actual development of actual, working, nuclear technologies. I refer to you another part of the IEA site, which discusses where all energy basically comes from. Click here. As you can see, about 7% of all world energy is basically nuclear (note that we can basically argue that ?none? of this is US nuclear, since the ban and all that). It grew about 6% (obviously I'm rounding, just go to the sites) in about 3 decades, yet, um, huge ammounts of money has been thrown into nuclear research.

Granted, a jump from 1.3% to 11% (for OCED countries) in about 3 decades is fairly impressive when you talk about implementation, but it's hardly impressive when you look at how costly it was from the RD&D perspective.

soph · 2003-05-10 17:58:02

Actually, there are a number of US plants, there are just no breeders. I believe Bush actually approved the construction of new reactors.

Josh Cryer · 2003-05-11 02:24:14

Hmm, you're right. I'd thought that the anti-nuclear lobby had prevented them from being built at all with that ban, and there were like only a dozen (despite the fact that personal experience with moderate environmentalists suggested that they wouldn't mind clean reactors). Guess I should've read into that further (seems my original inclination was correct).

I was thinking that the trend we see with nuclear is that it's replacing fossil fuels (for basic energy generation) as the need arises, which tends to be how the market works. In fact, looking at the charts, the trend is very obvious, as the nuclear band becomes wider, and the other bands stay about the same. This only makes me conclude that the anti-nuclear lobby isn't that powerful after all.

But none of this answers why nuclear R&D is so friggin expensive. We have basically a growth rate of .2% a year for the past thirty years... on a technology that has eaten up 58.8% of all energy R&D expendature in the same time period!

I spent a little bit of time compiling a basic chart showing where the money has went over the past 30 years or so, as I was waiting for my brother to call so that we could do a 3-way mothers day thing. Guess that didn't happen (the mothers day thing- not the chart, as you'll see below).

Anyway, this is basically what I'm trying to point out (this can't be pretty printed, unfortunately, but you'll make sense of it- this is all US dollars, rounded of course, so don't complain about the percentages being off by .3%):

Conservation: 16956990000 / 6.9%
Fossil Fuels: 33038553000 / 13.5%
Renewables: 19811293000 / 8.1%
Nuclear: 143844275000 / 58.8%
Storage Tech: 7426103000 / 3%
Other Tech: 23193409000 / 9.4%
Total: 244271100000

I'm sorry, but that's hardly reflective of a technology that's only grown .2% a year. Blackhole, indeed. I bet any kind of technology could grow at .2% a year with that kind of money... at least renewables would be potentially viable for as long as the sun shined.

Of course, this is diverging from the topic (must I always do this?), but I think the other side of the point is quite important. It could suggest that nuclear technology requires lots of R&D by its very nature. I question the feasiblity of large ship building facilities or whatever. Especially since it costs so much currently to build a few power plants; objects which basically sit on the dirt, and don't have to be built to withstand the rigors of space while jetting hot material out their ass end, all the while trying not to irradiate everyone within the vicinity.

Then again, Mini-Mag Orian could change that (due to its rather simpilistic design). But I think I'll wait and see.

dickbill · 2003-05-11 10:15:41

I was thinking that the trend we see with nuclear is that it's replacing fossil fuels (for basic energy generation) as the need arises, which tends to be how the market works. In fact, looking at the charts, the trend is very obvious,

Not related to space but rather, to the H2/cars presidential anouncement. Total replacement by hydrogen cars requires more electricity production than the current US production.
At first, right now, it seems that only nuclear electricity could fill such a project. It seems at least, but if we consider the possible nuclear FUSION produced electricity, then, the issue is different.

Indeed, Imagine that nuclear fusion is able, in 20 years, to provide more power than it consumes, then, it is not worth to build tenths of fission based nuclear plants to filled that gap of 20 years. It would generate too much radioactive nuclear wastes and would cost too much in development, just to be abandonned a couple of years later.

So, if the H2 cars projects goes on, which is good, more electricity is necessary than the USA could produce. Then, I think that the solar energy could be enough to momentarily fills the need, even partially. That would be good timing to have clean cars and clean electricity produced.

But if it happens that H2 cars could be massively available in the next 20 years and scientists say that nuclear fusion electricity cannot be ready in the next 50 years, then, we have a problem.

Josh Cryer · 2003-05-11 11:50:44

Well, since no one is biting the argument I'm making here, I guess it doesn't matter so much that we diverge the topic yet again. Anyone may of course feel free to tell me what they think. BTW, I actually did manage to get that mothers day thing pulled off. So Happy Mothers Day to all you mothers out there.

Anyway, I'm critical of the presidential announcement, because it's just an extension of a mandate that was already there, it's not like the president is saying, ?New renewable economy, tomorrow!? More like, ?A little bit of a renewable economy some time in the distant future.?

Personally, I could care less about creating hydrogen itself, because hydrogen is hard to store. Alcohols have shown to be the best way to store hydrogen for electric converstion.

dickbill · 2003-05-11 13:09:35

Personally, I could care less about creating hydrogen itself, because hydrogen is hard to store. Alcohols have shown to be the best way to store hydrogen for electric converstion.

Yes hydrogen is difficult to store, but in the long term, it is worth to invest in it. Better than hydrogen could be electric cars, but the problem to store electricity is not less than to store hydrogen.

Again, I hope that when nuclear fusion is available, old problems like reusable/durable versus fossile carborant will be irrelevant. Even solar energy will be more expensive than the nuclear fusion energy. By that time, we have to deal with ecological problems, and yes, solar energy is certainly a good way to resolve environmental problems.

RobertDyck · 2003-05-11 16:35:52

I don't think the ban on breeder reactors has anything to do with competition with fossil fuel, it's because breeder reactors produce plutonium. The U.S. government has an obsession with ensuring no one else has nuclear weapon technology. Uranium can be adjusted to make it suitable for weapons; a high concentration of U235 vs. U238 is required to create a bomb. Ideally, a bomb would have 99% or greater U235 although a bomb could use less. U.S. nuclear power plants use uranium with only 2% U235, which is just not able to explode. Canadian reactors use 0.7110% U235 because that is what comes out of the ground; therefore does not require enrichment technology. Lack of enrichment technology means nuclear weapons are not possible, and bypassing the enrichment step means operation is cheaper. However, all of the plutonium produced by a breeder reactor is Pu239. That means simple chemical separation can create bomb grade plutonium. The technology to create nuclear reactor fuel from the waste of a breeder reactor can simply be used to produce bomb grade concentration of plutonium. I could argue that the obsession about nuclear weapons is not necessary. The U.S. has nuclear weapons, and who started the war with Iraq? But let me cut off any come-back regarding any Iraq comments, and just say the end of breeder reactors has to do with limiting nuclear weapons proliferation, not competition with fossil fuels.

soph · 2003-05-11 17:22:16

But if the U.S. controls the breeders, what's the panic?

Josh Cryer · 2003-05-11 19:57:48

Yeah, I've read several articles where Carter has justified his position on breeders, and I can't say that it was really unfounded. The only thing that confuses me is that I thought that new breeder designs ate 99.99% of the fuel or something along those lines, and were just basically ridiculously efficient. Anyone care to shed some light on the situation? If my recollection was correct, and that comment is true, then the ban has no reason to continue.

I'm pretty sure that I never said that the breeder reactor ban had an underlying conspiracy behind it, and it's not like I'm not a fan of conspiracies, so I would've said that oughtright if I thought there was enough evidence to suggest that.

And soph, I think the answer to that is simple. Four words: pain in the ass.

Bill White · 2003-05-12 10:54:04

But if the U.S. controls the breeders, what's the panic?

Suppose the US deploys numerous commercial breeder reactors to produce electric power. How do we then tell Iran they cannot generate electricty that same way?

Just like Robert said, fast breeders make PU-239 - a great bomb making material.

RobS · 2003-05-12 13:18:46

When breeders were discussed and rejected during the Carter administration, the main proposal was for a liquid sodium cooled fast breeder reactor. This was about the time of Three Mile Island and all the fear of radiation and reactors it "bred" (no pun intended). Liquid sodium, if it comes in contact with water, generates hydrogen gas and explosions. There was a huge fear that liquid metal (sodium, lithium, potassium) fast breeders were extremely dangerous, and it was a time when the public feared nuclear power. So bye, bye, breeders.

Twenty-five years later there are new options that are safer and better, so maybe the breeder issue needs to be reconsidered. Proliferation issues certainly are worse right now, though.

-- RobS

RobertDyck · 2003-05-12 14:11:17

Nuclear waste reprocessing uses the same concept as a breeder reactor. Instead of using radiation to convert a practically non-radioactive isotope of uranium into fissile material, a reprocessing plant uses radiation to transmute highly radioactive waste products into non-radioactive material. This is the only way to truly eliminate radiation. If we want a clean environment, nuclear waste reprocessing is necessary. If we have waste reprocessing technology, why not a breeder reactor? Then there is the issue that a CanDU (Canadian Deuterium-Uranium) reactor is the most efficient producer of plutonium next to a breeder, and THE most efficient producer of tritium, period. I'm sure other heavy water reactors would have similar properties. Banning breeder reactors may slow the production of plutonium, but won't eliminate it. The U.S. military is blending plutonium from nuclear weapons pits into reactor fuel rods to permanently dispose of the plutonium. This demonstrates the mania to eliminate plutonium as a bomb making material, but new plutonium is created anyway in reactor waste. I was going to say it is generated in heavy water reactors, but the article Bill White linked indicates the breeding process required fast neutrons. The lack of moderation is why fast breeder reactors require highly enriched uranium. The high concentration of U238 in CanDU reactor fuel is probably why there is absorption of neutrons by the U238. Since plutonium will never go away, wouldn't it be better to accept it, work with it, and regulate it? That means carefully monitoring where spent fuel rods from all nuclear reactors in the world go. In fact, reprocessing spent fuel rods to transmute highly radioactive waste can be fuelled by plutonium in those same fuel rods, and new plutonium bred from the high concentration of U238 still in those same fuel rods. That means a reprocessing plant can fuel itself from the waste alone, but only if it is constructed as a breeder reactor.

This would mean permanent elimination of radioactive nuclear reactor waste, and careful monitoring of all spent fuel from all reactors in the world would mean greater safety from rogue nations producing nuclear weapons. Convincing the administration to do this would be a highly political matter.

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