NERVA...42 years later.

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NERVA...42 years later.

Postby David McKee » Thu Jul 10, 2014 10:20 am

Wanted to know if anyone here had heard of this - and what a sad waste that this technology has sat here unused for 42 years. Hopefully this picture posted.

Anyway, NERVA was a nuclear engine developed by NASA and the Energy department, then Nixon put the Kibosh on it - right after it proved that it was a viable long distance space engine.

NERVA ENGINE.jpg
Nerva Engine
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Re: NERVA...42 years later.

Postby Donovan Ready » Thu Jul 10, 2014 12:14 pm

Yessir, it was shelved because of the danger of core breach in atmosphere. It had a high specific impulse, but I think they wanted all the fissiles to be in direct governmental control, wisely. Same with SNAP generators that use Pu239 as the fuel. They're viable for years, but Plutonium is getting hard to come by...

A member at my Joint has a good idea for a solar thermal rocket that would still give good performance out to about Saturn's orbit if his assumptions and calculations are good. See here for the thread.
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Re: NERVA...42 years later.

Postby Doug Coulter » Fri Jul 11, 2014 11:20 am

Well, right now the mission doesn't really exist for the former anyway, at the moment. Though it would be nice to speed things up if you had humans along - so they see less radiation from space (and the sun), we're not planning that (outside Elon Musk's hopes) anytime soon, and yes, a core breach in the atomsphere (rockets still do blow up now and again) would be a pretty large disaster...though perhaps not so large as some think, as you have to have done some fission to have fission byproducts...the initial reactants need not be all that hot. Things with million and billion year half-lives aren't that nasty, it's the results of fission that hit the "sweet spot" for harming humans the worst - stuff that has a half-life on the order of a human lifetime is as hot as you can get and still stick around long enough to do lots of harm. That's why people freak out about the hot cesium and stronium isotopes when they leak. Those are "just right" for killing people.

This is why the push in radiology for very short half-life tracers for PET and other things. You need less to get the signal out of the noise for the detectors, and it's gone quick out of the test subject, so they get less of a dose than they would with a longer-lived isotope - it either decays quick after the test, or in the best case, is flushed out of the body quickly by normal processes. That's the other evil of some things like cesium/strontium, or even Pu 239 or U - they tend to concentate in bones as the body can't chemically tell they're not calcium or something else supposed to be there. That makes them double-extra-nasty.

SNAPs or RTG's never did and won't use Pu239. It simply doesn't decay quickly enough to make enough heat for the thermocouples (too long a half-life). That's of course why the Japanese and others use it in reactors as part of MOX - burn up all those nuclear weapons that won't go away on their own, more or less. They used Pu238, among other things, at leat for the non-fission odd numbered ones, which is indeed hard to get your hands on these days, as it's a byproduct of reactor fuel reprocessing, something we don't do in this country for political (supposed non-proliferation) reasons at the moment - even though it would sure cut down on the poundage and length of storage required for nuke waste to the point of making it practically a non-problem outside the self-panicking public when the word nuclear is used (why we had to rename nuclear magnetic resonance imaging to just magnetic resonance imaging, for example - NMR become MRI just for "politics" even though it's the same thing and doesn't even involve ionizing radiation anyway). They do (or did) in Japan and elsewhere, but in the former case have managed to have some pretty scary accidental criticality accidents when someone decided to speed up the process by using larger batches of dissolved reactants (which of course were dissolved in aqueous solution - water - a moderator). Of all people, you'd think the Japanese would have a better record of safety - they are rule followers, and well, have seen what bombs do first-hand. Back to RTG's - they are a lot easier to make rocket-blowup-resistant. We've even had them crash from orbit and cleaned it up fine (actually, the Russians had one crash in Canada, IIRC).

Solar this and that tend to only work close-in (in solar system terms), even though you can make one heck of a nice mirror with what amounts to a baloon that is half silvered and weighs almost nothing.
Inverse square law just kills you on those. Inner solar system, yeah, it's a good idea perhaps. As solar sails might be at some point, for things where you're not in a hurry - and can afford a big superconducting magnet loop to act as a "keel" so you can steer.

I've always wondered why ion engines aren't more in play than they are. Yes, they need energy of some kind to run... Actually, my real question is why concentrate on heavy ions when you could, without too much difficulty, take advantage of relativistic mass gain for the particles accelerated, and therefore not need to carry heavy ions (or expensive ones, like the currently favored Xenon). I could be wrong, but I think the math works out there, if you've got the energy. Of course, if you've got essentially infinite cheap energy, you could just use photons. Kind of energy-expensive, but possible. There have been proposals to boost spacecraft from the earth with photons, since in that case, the heavy photon sources can stay on the ground.

Pretty good reason to be working the fusion angle, IMO. We'll get there at some point almost for certain, though it might not be tokomaks that do it. Miley's book even proposes using a modified fusor for it - you make it asymmetric so one of the jets is your "output". Dunno about that one, but it's in print in several places and written up by pretty credible "authorities" on the subject.

Of course, fusion that makes neutrons, as the stuff I'm working with does, has it's own set of hazards. Due to a mostly-unexpected breakthrough here, I got myself a real serious dose and don't feel really good right now as a result - about .1 Sievert in about 30 seconds when a test worked a lot better than it had any business doing - I got "lucky", and was stupid enough to spend 20-30 seconds trying to figure out why all my gear "blanked" before just turning the thing off. As a result, I've had to spend a lot of time re-examining all aspects of operator safety here, and doing some boring hard work on a few levels so as to be able to continue my work. Gee, usually I go for a factor of 10 or more, and get 2. This time I went for 5 and got 2800 (roughly, it broke my stuff and now I'm building all the test/measurement stuff back and recalibrating it).

One that bit me on the ass...we had nearly a ton of "cerro safe" around. It has 12% cadmium, which makes a hell of a capture gamma and has more or less 100% cross section for thermal neutrons. Oops.
Great for shielding X rays - horrible in the presence of neutrons. In that case, it acts like an amplifier for human-damaging radiation.

All gone now, but that was one heck of a job of moving and hauling. My floor would simply not hold up the amount of lead required to stop those energy gammas (megavolt class), and I can't do my magic from behind 20 foot thick concrete (or afford the 'crete and the room). Too much of what I'm doing depends on proximity of the mark 1 eyeballs and so on. Even with the new scope - it has to be close to the RF type signals - you don't just hang an extension cord on a probe - so my efforts of late have involved remote control of the scope, so it can be on the "hot side" of things in proximity to the signals, while I watch from the other side of the shielding.

In space, you could make that square law work for you - many designs for various nuke powered ships show the reactors a great distance from the living space - it's cheap to hang it out on a long rod somewhere when you are talking tiny gee forces, as you are in that situation. And even .1 g is quite a lot if you can have it continuously in terms of how long it takes to go a long distance. You can even arrange it so the long rod looks like a very thick shield between the reactor and the people - even if it's low Z and light, there's still enough length to stop or scatter most of the bad stuff.

But in re space travel in general - the problem is political more than scientific, as has been shown when private enterprise gets involved and makes it affordable (less un-affordable?). There's also this misconception that NASA gets a lot more dough than they do. I recently read that most people think they are 24% of the budget - it's more like half a percent (of the budget - which doesn't include most governement spending - wars are always "extra" and let's not even start with SS or medi-whatever) . Not that they are the height of competance and efficiency with money. Long ago they flushed out most of their best engineers and replaced them with wet behind the ears newly minted PhD's and have had a lousy track record of space exploration ever since. I know this as when those guys came on the market - I hired some of those engineers and heard the story first hand. That's not to say they haven't done amazing things with earth exploraton from space, just that they kinda lost their way on creating that vision that humans could spread through the solar system and the galaxy. We humans do need to dream, and to explore.

I'm old enough to have watched the first moon landing - live. One thing that pisses me off more than most other things - there was the implicit promise that someday I'd get a ride like that. Some years later it was obvious that promise was never going to be kept before I got too old, and it was all a political stunt for cold-war purposes. Politics!
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Re: NERVA...42 years later.

Postby Donovan Ready » Fri Jul 11, 2014 12:46 pm

My bad on the Pu239; I was writing off-the-cuff. :oops:

As to the moon landing and every other mission that was televised, I was there too. When Challenger went up, we all drove in to Rock Springs from the ranch I was building a house on to have breakfast and watch the launch. I don't remember anything after the explosion..
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Re: NERVA...42 years later.

Postby Doug Coulter » Fri Jul 11, 2014 12:59 pm

I experienced a "strange coincidence" when the Challenger blew. That's all I can call it. I was unaware of it at the time - I'd just recently moved down to the country, and was at the time living in a barn with a horse on a friend's property (it was really just about that low a time in life, but fun anyway). I was walking down the rutty dirt road to his house for, yeah, breakfast when it happened. And suddenly, I was on the ground, writhing - I'd slipped a disc or something. My yells brought help to get indoors, and I got the news because they'd been watching it - I only saw the re-run. I'll never forget that one, and always wonder just what happened there - I was young and pretty healthy then (good thing - homesteading turned out to be far more work than I'd thought it would be and I needed to be in good shape to do it), no reason to toss out my back just walking, and that hasn't happened before or since. It sure hurt, though, and for a long time. I don't have any credible theory why that should have happened, other than in a big universe, rare things happen often by pure chance. Sure seemed weird, though. It kind of became a gossip item here in the small community I still live in.
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