NASA returning to NERVA?

Point out news stories, on the net or in mainstream media, related to polywell fusion.

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GIThruster
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NASA returning to NERVA?

Postby GIThruster » Thu Feb 05, 2015 4:44 pm

This was my recommendation to the Augustine Commission. I'm completely surprised to see it got any traction.

http://www.dailymail.co.uk/sciencetech/article-2938278/Is-future-space-NUCLEAR-Nasa-developing-new-rockets-send-astronauts-new-corners-solar-system.html
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Tom Ligon
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Re: NASA returning to NERVA?

Postby Tom Ligon » Thu Feb 05, 2015 7:32 pm

They think about it from time to time. When I first joined EMC2, there was a proposal kicking around NASA to look at nuclear options for getting to Mars. The three on the table were NERVA, a fusion scheme based on tokamaks, and Dr. Bussard's proposals using a Polywell. I think they called it Strategy F (Fission or Fusion), but it does not seem to have ever gone far enough to raise it to public attention.

Two of the three were Bussard projects, since he made the original Rover proposal when he was only 24.

He said all the reactors from Rover thru NERVA are stored under a mountain in Nevada, cooling off, waiting for someone to realize that the program was nearly ready to fly when Congress decided Mars was not our goal anymore.

The article is misleading (no surprise for the Daily Mail). It is not that the thrust is higher, it is that the engine can make the same thrust longer. Specific impulse of these hydrogen-heating gas core fission reactors was around 860 seconds. The Space Shuttle main engines were 450 seconds.

Clarke's description of the engines of the Discovery (2001, A Space Odyssey) are deliberately a little vague, but pretty much fit an advanced version of NERVA. Clarke, in the late 60's, thought it was entirely possible for us to build Discovery by 2001, and I think he was right. We just didn't.

glemieux
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Re: NASA returning to NERVA?

Postby glemieux » Thu Feb 05, 2015 8:03 pm

Interesetingly, there was a talk on nuclear thermal propulsion at the recent AAS GNC conference that I just got back from:

Guidance, Navigation, and Control Considerations for Nuclear Thermal Propulsion by Michael Houts (NASA MSFC)

For what it's worth, it was a interesting talk, but not one that spurred many questions from the conference attendees. I have to admit I used most of the time during that talk to catch up on work on my laptop, but the most interesting tidbit that I got from it was the admission that US is no longer an innovator in nuclear fission energy the way it use to be. I believe the author's opinion was that this state is unfortunate given the great thrust/weight ratio that would enable crewed missions to Mars. He also stated that he believes that opposition to RTGs (and by extension other forms of nuclear space power) is waning given the absence of protesters for the launch of MSL compared to Cassini.

GIThruster
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Re: NASA returning to NERVA?

Postby GIThruster » Thu Feb 05, 2015 8:34 pm

Tom Ligon wrote:It is not that the thrust is higher, it is that the engine can make the same thrust longer.

That is really a mission level decision. Whatever they build should be able to do either/or. Typically with thermal rocket mission profiles you want to burn hard early for shorter travel times and with nuclear electric like ion you go for longer burns. Either way with any nuclear thermal rocket the chief advantage is the higher Isp.

gemieux wrote:. . .the most interesting tidbit that I got from it was the admission that US is no longer an innovator in nuclear fission energy the way it use to be.

I have to wonder what is considered "innovative" at this point. Transatomic is still working their liquid salt reactor that is much safer and <1/2 the cost of a Westinghouse light water reactor. India and China are both scooping us on Thorium reactors (also salts), but they will likely not be so small or cheap. So only time will tell.

Wasn't there recently an announcement from DOE they were going to look at/fund Thorium too?

BTW, IIRC Michael Houts at Marshall also did some work in Hypersonic GN&C. I bet he's a really interesting guy. Was he talking neural nets?
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis

glemieux
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Re: NASA returning to NERVA?

Postby glemieux » Thu Feb 05, 2015 9:55 pm

GIThruster wrote:
gemieux wrote:. . .the most interesting tidbit that I got from it was the admission that US is no longer an innovator in nuclear fission energy the way it use to be.

I have to wonder what is considered "innovative" at this point. Transatomic is still working their liquid salt reactor that is much safer and <1/2 the cost of a Westinghouse light water reactor. India and China are both scooping us on Thorium reactors (also salts), but they will likely not be so small or cheap. So only time will tell.

Wasn't there recently an announcement from DOE they were going to look at/fund Thorium too?

BTW, IIRC Michael Houts at Marshall also did some work in Hypersonic GN&C. I bet he's a really interesting guy. Was he talking neural nets?

Wow, that certainly would have been cool if he had mentioned neural nets, but alas, no. It was a straight talk on nuclear thermal propulsion.

I follow the LFTR/MSR forums and I don't remember seeing that the DOE was looking into funding Thorium, but I could certainly have missed it. If you find the reference, point me to it please :).

GIThruster
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Re: NASA returning to NERVA?

Postby GIThruster » Thu Feb 05, 2015 10:18 pm

glemieux wrote:I follow the LFTR/MSR forums and I don't remember seeing that the DOE was looking into funding Thorium, but I could certainly have missed it. If you find the reference, point me to it please :).

This might be what I was thinking of:

http://en.wikipedia.org/wiki/HT3R
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krenshala
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Re: NASA returning to NERVA?

Postby krenshala » Fri Feb 06, 2015 12:20 am

The article on Universe Today was a bit better.

Tom Ligon
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Re: NASA returning to NERVA?

Postby Tom Ligon » Fri Feb 06, 2015 2:09 am

Much better!

williatw
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Re: NASA returning to NERVA?

Postby williatw » Fri Feb 06, 2015 2:19 am

Perhaps I missed it but I was surprised to see not one word about "Project Timberwind":





http://en.wikipedia.org/wiki/Project_Timberwind


I is after all more recent than the original NERVA; from 1987-1991. It was primarily designed I believe to be an upper stage of some kind of chemical rocket to launch heavier Star Wars (SDI) components to earth orbit rather than deep space applications, but still.

93143
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Re: NASA returning to NERVA?

Postby 93143 » Fri Feb 06, 2015 10:20 am

Timberwind was a pebble bed design and had trouble with hot spots. Dumbo might be a better option for future development; same general idea but a structured core.

GIThruster
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Re: NASA returning to NERVA?

Postby GIThruster » Fri Feb 06, 2015 2:44 pm

Timberwind was designed for throw away missile type applications and goes into meltdown pretty easily. Vanilla over at NSF did a very detailed analysis back in 2008 of why it is probably the most dangerous fission design ever created, but that it doesn't matter when you want it to go all BOOM anyway.
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis

Tom Ligon
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Re: NASA returning to NERVA?

Postby Tom Ligon » Fri Feb 06, 2015 5:20 pm

I'll offer a tidbit here that RWB gave me while I was at EMC2. He wormed his way into the nuclear profession by studying heat exchanger design. Nuclear physics was largely classified and hard to study at the time, but it was still the age of steam and those courses were available, and useful to fission applications. He was already an expert on rockets by the age of 16, so putting the two together was a natural.

He designed Kiwi reactors with rectangular cross section gas channels. The reason he did so was a subtle channel stability issue that a heat exchanger engineer would get and most physicists would miss. If you have a lot of parallel circular cross section channels, and there is a small blockage in one of them, it will get less flow than the rest. That flaw can be a small hot-spot which disrupts flow. If the flow drops in that channel, the hot spot gets hotter and the channel will block itself off completely. The result is overheating around that channel.

A small flaw in a rectangular channel causes the gas to just go around the flaw, and flow in the channel is affected much less.

He said that when he left the project, nobody understood why he had used rectangular channels, and they didn't care for them much. Everybody knew that steam engine boilers had round channels for the flue gas, so that must be how to build them. They went to round channels and had nothing but problems with them until they finally figured it out. So if you get a chance to see drawings for some of those problematic designs, see if you can spot channel shape.

The early designs with rectangular channels did have a problem of shedding radioactive material into the gas stream. They made a mess of their test pads, but, as suggested, if intended to launch ICBMs, well, we were all gonna die anyway. The landing area would be much worse. And spewing radioactive junk into space on an interplanetary mission is not so much of an environmental problem.

TheRadicalModerate
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Re: NASA returning to NERVA?

Postby TheRadicalModerate » Wed Feb 11, 2015 8:33 pm

Tom Ligon wrote: And spewing radioactive junk into space on an interplanetary mission is not so much of an environmental problem.

I think the Orion project studied this issue and determined that you had to be effectively outside the magnetosphere before you dumped any kind of radioactive stuff outside the spacecraft or it all wound up in the atmosphere at the poles.

Also:
The article is misleading (no surprise for the Daily Mail). It is not that the thrust is higher, it is that the engine can make the same thrust longer. Specific impulse of these hydrogen-heating gas core fission reactors was around 860 seconds. The Space Shuttle main engines were 450 seconds.

Just to clarify, the thrust is a lot lower, and thrust-to-weight is horrible. An SSME generated 2090 kN of thrust and had a thrust-to-weight of 73. A NERVA/XE generated 334 kN and had a T/W of about 1. But yes, the specific impulse is a lot higher, which gives you a lot more delta-v for the same wet mass.

Skipjack
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Re: NASA returning to NERVA?

Postby Skipjack » Thu Feb 12, 2015 6:37 pm

TheRadicalModerate wrote:
Tom Ligon wrote: And spewing radioactive junk into space on an interplanetary mission is not so much of an environmental problem.

I think the Orion project studied this issue and determined that you had to be effectively outside the magnetosphere before you dumped any kind of radioactive stuff outside the spacecraft or it all wound up in the atmosphere at the poles.

Also:
The article is misleading (no surprise for the Daily Mail). It is not that the thrust is higher, it is that the engine can make the same thrust longer. Specific impulse of these hydrogen-heating gas core fission reactors was around 860 seconds. The Space Shuttle main engines were 450 seconds.

Just to clarify, the thrust is a lot lower, and thrust-to-weight is horrible. An SSME generated 2090 kN of thrust and had a thrust-to-weight of 73. A NERVA/XE generated 334 kN and had a T/W of about 1. But yes, the specific impulse is a lot higher, which gives you a lot more delta-v for the same wet mass.

A little bit of radioactivity in the atmosphere is completely irrelevant. Besides, the hydrogen reaction mass barely gets radioactive anyway. Also want to point out that subsequent projects to NERVA demonstrated much higher T/W than 1, high enough to SSTO.

GIThruster
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Re: NASA returning to NERVA?

Postby GIThruster » Thu Feb 12, 2015 9:11 pm

Skipjack wrote:A little bit of radioactivity in the atmosphere is completely irrelevant.

It's not irrelevant politically, and politics is what decides hope the money gets spent. An open cycle nuclear thruster will never get funding. Even a closed cycle can't be started until in space or the political consequences would be to stop it.
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis


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