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The US government is taking a step toward space-based nuclear propulsion

arstechnica.com

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Re: The US government is taking a step toward space-based nuclear propulsion

#171

Post by credit_guy »

AtlasBarfed wrote: post #137
credit_guy wrote: post #108

For anyone who wants a refresher on the UNS nuclear thermal rocket propulsion program from the '60s, here's the final report. It's a very good read: https://ntrs.nasa.gov/api/citations/19920005899/downloads/19... For this new initiative, I can see 2 big differences. On one hand they will use medium enriched uranium (up to 20%), while the original program used highly enriched one (85%), so it's going to be more challe…

LFTR can be turned off pretty easily.

Yes, but the liquid fluoride thorium reactor does not get anywhere close to the temperature you need for a nuclear thermal rocket. It might get close to 1000 ℃, but you need about 2200 ℃ to get the 900 seconds specific impulse that makes nuclear thermal rockets so appealing. At that temperature that liquid salt has long vaporized.

Re: The US government is taking a step toward space-based nuclear propulsion

#173

Post by aziaziazi »

adastra22 wrote: post #170
aziaziazi wrote: post #164

Earlier quoted context omitted.

Oceans, marine fauna and marine flora are part of the biosphere.

None of those exist in the regions where these satellites and rocket stages crash. These are natural dead patches.

Any evidence/reference to back this up?

Oceans are the cradle of life and are still populated by fishes, mammals, zoo and phytoplancton even away from coastlines.

http://comlmaps.org/gallery/footprints/

Re: The US government is taking a step toward space-based nuclear propulsion

#174

Post by wkat4242 »

aziaziazi wrote: post #34
somenameforme wrote: post #7

Earlier quoted context omitted.

I think the obvious concern would be failure scenarios. There will always be failures in space technology. As space expands exponentially (as it is likely to do so in the future), failures will become relatively regular. So the obvious question would be what would happen if a nuclear rocket, with reaction in process, crashed to Earth. Or even if it broke up in the atmosphere.

It already happened with Kosmos 954 and will probably happen again soon: ~20 other satellites had been sent in space with the same tech. Kosmos crashed away from (human) life centers but that was a huge stroke of luck. Research area was 100k+ km2. Launches are less to be feared because they are oriented toward sea and the most critical moment are the first minutes. The device discussed is intended to travel away from…

Not soon. Most of these other rorsat reactors have been put in a parking/disposal orbit where they'll last a long time (I forgot how long bit I think it was in the order of thousands of years)

I'm kinda surprised the soviets even thought of the environment in that way.

Re: The US government is taking a step toward space-based nuclear propulsion

#175

Post by adastra22 »

aziaziazi wrote: post #173
adastra22 wrote: post #170

Earlier quoted context omitted.

None of those exist in the regions where these satellites and rocket stages crash. These are natural dead patches.

Any evidence/reference to back this up? Oceans are the cradle of life and are still populated by fishes, mammals, zoo and phytoplancton even away from coastlines. http://comlmaps.org/gallery/footprints/

Not these areas.

https://www.rnz.co.nz/international/programmes/datelinepacif...

Abyssal zones of the ocean are only populated by creatures that feed on hydrothermal vents, or dead creatures falling down from the surface. But the mid pacific has no hydrothermal vents and the surface is a dead zone due to human activity. So there is no source of food for life to exist here, and outside of the occasional whale fall it is truly dead.

Re: The US government is taking a step toward space-based nuclear propulsion

#176

Post by aziaziazi »

adastra22 wrote: post #175
aziaziazi wrote: post #173

Earlier quoted context omitted.

Any evidence/reference to back this up? Oceans are the cradle of life and are still populated by fishes, mammals, zoo and phytoplancton even away from coastlines. http://comlmaps.org/gallery/footprints/

Not these areas. https://www.rnz.co.nz/international/programmes/datelinepacif... Abyssal zones of the ocean are only populated by creatures that feed on hydrothermal vents, or dead creatures falling down from the surface. But the mid pacific has no hydrothermal vents and the surface is a dead zone due to human activity. So there is no source of food for life to exist here, and outside of the occasional whale fall it…

Terrifying, didn’t know there’s a second patch on the south. The census map in my parent post show this area populated by “predators” but not much zooplankton, so not sure what lives there. There’s also probably a bunch of debris from nuclear tests in this region.

Re: The US government is taking a step toward space-based nuclear propulsion

#177

Post by WalterBright »

marcosdumay wrote: post #172
WalterBright wrote: post #134

Earlier quoted context omitted.

How is H going to explode out in space?

Rockets don't work with H2 alone.

H alone is the propellant in a nuclear rocket. H needs an oxidizer to explode. No oxidizer, no explosion.

Re: The US government is taking a step toward space-based nuclear propulsion

#178

Post by lazide »

ridgeguy wrote: post #88
lazide wrote: post #72

Earlier quoted context omitted.

The real limiting issue tends to be materials in the reactor - at some point, every known material is a liquid or a gas and the reactor stops being an ongoing concern. Usually reactors run cooler by several orders of magnitude, as this is referred to as a ‘meltdown’ and people get snippy about the releases of radiation and expensive cleanup crews, etc. Space is more forgiving and has fewer HOA types, so they can go c…

Yeah, the materials issues dominate design basics. They've looked at HfC and HfCN as nuclear engine materials (m.p. ~3950°C), pretty exotic. I feel like if designers would drop their effort to wring out the last increment of Isp from nuke engines and reduce temperatures to ~2000°C, it would give faster development. There are many materials that can live in 2000° hydrogen for >100K hours. There's an old Rand study tha…

That does sound more reasonable!

Part of the issue I suspect why reasonable isn’t being considered is that I don’t expect anyone to have a reason to really use them right now regardless - all the nuclear propulsion designs have a high ‘fixed’ weight cost in the reactor, so would only make sense overall in a ‘hundreds of tons to Uranus ASAP’ type situation, where the overall weight for thrust can be lower due to the better fuel efficiency.

So far we thankfully haven’t had a reason to really need to do that right now.

And if we’re doing theoretical designs, why not make it ‘interesting’?

On a side note, if we’re considering crazy ideas - my favorite is the one that makes Project Orion seem clean!

https://en.m.wikipedia.org/wiki/Nuclear_salt-water_rocket

Any rocket which calls for ‘salts of plutonium’ as fuel has to be cool.

Re: The US government is taking a step toward space-based nuclear propulsion

#179

Post by ben_w »

adastra22 wrote: post #169
ben_w wrote: post #162

Earlier quoted context omitted.

"""There have been 2,121 tests done since the first in July 1945, involving 2,476 nuclear devices. As of 1993, worldwide, 520 atmospheric nuclear explosions (including 8 underwater) have been conducted with a total yield of 545 megaton (Mt): 217 Mt from pure fission and 328 Mt from bombs using fusion, while the estimated number of underground nuclear tests conducted in the period from 1957 to 1992 is 1,352 explosions…

The atmospheric tests are the only ones that matter in this context.

Depends on the details; in water, too close to ground water, near ground level and breaching the surface (Operation Plumbbob), and I don't have numbers for those.

But still, thousands of bombs were in fact tested, and the context here is testing a reactor that won't be on Earth at all via a diversion into "we can detect really small levels of radiation".

Re: The US government is taking a step toward space-based nuclear propulsion

#180

Post by db48x »

Loquebantur wrote: post #51
db48x wrote: post #39

Earlier quoted context omitted.

The thing to remember about that is that we can measure tiny amounts of radiation very cheaply, and tiny amounts are harmless. In fact we are bathed in a constant, but tiny, background level of radiation all the time. Thousands of nuclear weapons were tested all across the world, in the United States, in the Soviet Union, on Pacific Islands, etc, etc. The radiation from that certainly caused a small uptick in the bac…

Background radiation is categorically different than ingesting/inhaling radioactive substances with the latter many orders of magnitude more dangerous. The claim, nuclear testing related increases in radiation exposure not being relevant for public health is probably false. There are only very few studies with dubious reliability. The lifetime increase due to that nuclear testing is estimated to be 4.4 Millisieverts.…

We eat bananas all of the time. Bananas are delicious and nutritious, and they are known for containing lots of potassium. Well, some of that potassium is radioactive! It’s not very much radioactivity though. It is an amount which is easily measured, but which is not harmful enough to make eating bananas dangerous. This is true even though the potassium will be used to strengthen your bones and teeth. It will also be distributed to your muscles, red blood cells, skin, etc, etc.
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