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Why aren't we using nuclear thermal rockets?

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15 minutes ago, kerbiloid said:

We never know how much horse manure will be produced by the end of century in London.

Hmmm ... might be more than today ?

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12 minutes ago, wumpus said:

several sailors on the USS Reagan received "severe radiation sickness" due to being downwind while bringing in supplies.

Interesting. Zero mention of that in reliable sources. Lots of retired servicemen lining up for extra benefits with distinctly non-cancer symptoms, though.

2 hours ago, kerbiloid said:

Reading about how they were cleaning the station and patching its walls, I doubt very much.

Hey, the number comes from the same people who cite 52 as a total for Chernobyl.

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7 minutes ago, Green Baron said:

Hmmm ... might be more than today ?

https://www.historic-uk.com/HistoryUK/HistoryofBritain/Great-Horse-Manure-Crisis-of-1894/

"This problem came to a head when in 1894, The Times newspaper predicted… “In 50 years, every street in London will be buried under nine feet of manure.”"

(About predictions in technical sphere)

P.S.
Obviously the antimatter won't be used before the thermonukes as only they can give enough energy to produce it.
But once they appear...

Edited by kerbiloid

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1 minute ago, kerbiloid said:

Had to open my pc for google to read it ... but it is cool. I recall the city of Berlin steaming from dog excrements during a thaw after a long and hard winter.

 

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Due to the nature of how radiation works, we'll never know how precisely many people die younger than they would have because of radiation exposure from Fukushima.

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1 hour ago, mikegarrison said:

Due to the nature of how radiation works, we'll never know how precisely many people die younger than they would have because of radiation exposure from Fukushima.

Not just that. The really interesting low-level exposure is expected to lead to levels that are too low for statistical studies of cancer to detect.

It's like the thrust of the EmDrive, but with cancer.

And before you say "The EmDrive is ridiculous", so's the dominant Linear No-Threshold model for radiation exposure. It assumes absolutely no capacity for DNA repair... when we know there is.

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Back off the sarcasm and personal animosities, please. 

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1 hour ago, DDE said:

And before you say "The EmDrive is ridiculous", so's the dominant Linear No-Threshold model for radiation exposure. It assumes absolutely no capacity for DNA repair... when we know there is.

The problem is, just one DNA break could cause death. It very likely won't, but it could.

Bacteria are the same way. In theory, all it takes to kill you from some disease is one supremely lucky bacterium that manages to evade your defenses long enough to reproduce, and its supremely lucky offspring do the same, etc. until there are too many to fight off.

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They are not too low to detect, there exists for example a study (i am sure it is linked above) that detected a slightly increased thyroid cancer rate in new born, especially girls, but it was still at the upper range of the natural variability in comparative studies. But we cannot deduct from that that the radiation did not cause any fatalities until now, only that its contribution to cancer rates is still in the range of natural processes.

Otoh, hadn't there been such an accident, the cancer rate might have been at the lower end of the natural variability. In this case the difference could be attributed to the accident. Of course, such a comparison can not exist, there is only one timeline.

Now both sides can stand up and say "See it was nothing, haha" and "That killed hundreds and many more in the future, don't you see ?". The first version can serve the purpose of rejecting responsibility, the second one can be basis for accusation of cover-up.

It is, as is the windshield of my car after a short rain, unclear, as i had to assert today. That problem can be solved tomorrow with acquisition of new windshield wipers :-) (Edit: just trying to be funny, no sarcasm !)

Edited by Green Baron

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3 hours ago, mikegarrison said:

Due to the nature of how radiation works, we'll never know how precisely many people die younger than they would have because of radiation exposure from Fukushima.

Epidemiology studies would retrospectively look at cancer deaths in the affected area and compare to similar demographics elsewhere in Japan, and look for a pattern. You'd likely not see anything until people with exposures reach their 50s+.

The point is that absolute deaths don't matter with respect to power production, it's deaths per unit power produced, since ALL forms of power production involve a non-zero mortality rate.

If rockets result in 1 death per 50 launches (that's a lower limit on actual launches and related deaths), then a spacecraft that requires additional launches for huge solar arrays might be substantially more risky than a single launch of a nuke with a slightly higher risk (assumed, for argument) given a launch failure.

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17 minutes ago, tater said:

The point is that absolute deaths don't matter with respect to power production, it's deaths per unit power produced, since ALL forms of power production involve a non-zero mortality rate.

Well, but for solar you must really fetch an argument from far, while for fossil and nuclear there are direct connections.

17 minutes ago, tater said:

If rockets result in 1 death per 50 launches (that's a lower limit on actual launches and related deaths), then a spacecraft that requires additional launches for huge solar arrays might be substantially more risky than a single launch of a nuke with a slightly higher risk (assumed, for argument) given a launch failure.

Lets stay in the inner solar system. Is solar really heavier than nuclear ?

If i recall we did a calculation in the past in this forum, and the result was surprisingly on the solar side. Of course, for a journey to Jupiter conditions change.

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20 minutes ago, Green Baron said:

Well, but for solar you must really fetch an argument from far, while for fossil and nuclear there are direct connections.

No, you don't.

People die mining materials for both. People die in constructing plants (or installing on a house). People die in working on continuing plants. They are all equally dead. If more 100X people are required to work solar for a given power output, and the death rates are identically low for both (both are incredibly safe), then solar will have 100X the deaths.

Maybe solar uses 1000X more workers per power, and is 100X safer as a workplace... it's still then 10X worse per unit power. Or it's 100X as many workewrs per power, and 1000X safer---still identical deaths to nuclear.

25 minutes ago, Green Baron said:

Lets stay in the inner solar system. Is solar really heavier than nuclear ?

For the Moon, you have a 2 week night. No solar. There are places where we might be able to have nearly 100% solar, but we have yet to land there (crater rim might be sketchy, and have substantial risks to human life itself). Nukes are an enabling tech, particularly for power-hungry ISRU schemes. Ditto Mars (Opportunity vs Curiosity right this second as the object lesson).

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12 minutes ago, tater said:

For the Moon, you have a 2 week night. No solar. There are places where we might be able to have nearly 100% solar, but we have yet to land there (crater rim might be sketchy, and have substantial risks to human life itself). Nukes are an enabling tech, particularly for power-hungry ISRU schemes. Ditto Mars (Opportunity vs Curiosity right this second as the object lesson).

I don't think you want to use opportunity as an example of a solar-powered probe having difficulties. After all, it was designed to run for 90 days and eventually lasted more than 5000.

Edited by mikegarrison

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1 minute ago, mikegarrison said:

I don't think you want to use opportunity as an example of a solar-powered probe having difficulties. After all, it was designed to run for 90 days and eventually lasted more than 5000.

It was (is? (finger's crossed) a great probe. But for a human mission (really the point of NTP, not needed for robots), a random storm that kills PVs is possibly fatal. If the ISRU needs to generate large amounts of power, and ou check the ISRU production rate to make a go-no go decision on launching the crew vehicle, what happens when a storm kills PV output, and the tanks won't be topped. Do we have to make sure ISRU can fill tanks in under 2.14 years? Is that doable with solar?

The point was that a random storm can kill PV power production. When such a storm happens is... random. It happened to take a long time to kill Opportunity, had the same storm happened on Sol 1, Oppy would have died that day.

Relevant to Mars missions, it would be ISRU deployed to generate methane, likely (assume they bring the hydrogen), if they happen to have a nasty storm on an early day after the MAV lands and deploys solar for ISRU, then that MAV is toast. I suppose you have rovers to deploy, and maybe to clean... which is great, except they are now dead, too (unless they have RTGs).

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6 hours ago, tater said:

it's deaths per unit power produced, since ALL forms of power production involve a non-zero mortality rate.

(Excessive words have been truncated.)

While growing berries in a garden, some gardeners will fall down from the ladder.
While painting, some painters will inhale something wrong or slide on a spot of a color.
While babysitting a baby, some babysitters will touch the wires or leave the kitchen gas on.
Going to a shop for bread, you roll the dice when crossing the road.

Absolutely any occupation causes additional risks and deaths.

Edited by kerbiloid

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52 minutes ago, kerbiloid said:

(Excessive words have been truncated.)

While growing berries in a garden, some gardeners will fall down from the ladder.
While painting, some painters will inhale something wrong or slide on a spot of a color.
While babysitting a baby, some babysitters will touch the wires or leave the kitchen gas on.
Going to a shop for bread, you roll the dice when crossing the road.

Absolutely any occupation causes additional risks and deaths.

I've decided that breathing is risky, because of the chance I could breathe in hazardous particles. So I've decided to stop it. Breathing. Starting ... now.

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1 minute ago, mikegarrison said:

I've decided that breathing is risky, because of the chance I could breathe in hazardous particles. So I've decided to stop it. Breathing. Starting ... now.

Unbreathing is even more risky.

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Irl little mining is involved in the fabrication of solar cells, compared to classic industrial power generation and fuel hauling. In an ideal case one wouldn't even need conversion or grid connection. You make them once for 10-20 years of reliable generation, maintenance free lifelong, partly from recycling materials, except the cells themselves which need a little sand, sloppy spoken. Classic power otoh needs a constant flow and much more for initial investment for everything, including transport of fuel and generated power.

Many more hard and dangerously working people are needed for classic power generation and maintenance than for solar power. Which is an argument against the latter then if one puts economic turnaround over life quality. There is less turnaround in solar power fabrication and maintenance, that makes it unwanted in some countries (like spain). Lobby and all that. Consciousness is only slowly changing.

There is still far too much irrationality and constructed arguments involved. "People dying working for solar power" is non argument, and totally turns against the arguer.

 

For space application solar is ideal, light weight, reliable, maintenance free. I say, the only two arguments not to use it are if people don't want to and willingly take high risks, including outage in case of failures, or if there isn't enough solar radiation (beyond Mars).

 

Edited by Green Baron

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(I can't into xkcd, so a little story in pictures.)

Spoiler

solar-roof.jpg

maxresdefault.jpg

images?q=tbn:ANd9GcQ0M3lBfLuBxv6UfwRCsqwimages?q=tbn:ANd9GcSoAx84RQ1z-q2kB362eh2images?q=tbn:ANd9GcQwLfML1XZRki-KjIDioS4

water-contaminants-header.jpg

 

images?q=tbn:ANd9GcSubUQG8RSy_LyBQuA9Vjx 

images?q=tbn:ANd9GcT_oUOJG5NQ9GadZHRIiS9


 

An Earth desert.

Spoiler

images?q=tbn:ANd9GcTEjkPm5VE1ZamYcEb6EH_16256676-prickly-pear-bush-in-a-desert-p

A Martian desert.

Spoiler

images?q=tbn:ANd9GcQ8ux4_wBff8s_DUaj-m9I

 

Edited by kerbiloid

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Yes, dusting them is the only periodic (once a year here) maintenance they need. Which could be partly achieved with a repellent surface and electrostatic.

Edited by Green Baron

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56 minutes ago, Green Baron said:

Yes, dusting them is the only periodic (once a year here) maintenance they need. Which could be partly achieved with a repellent surface and electrostatic.

Factor in micrometeoroid damage and slow erosion from rads. Both are significant on an industrial scale.

Makes me wonder how they compare to helio-thermal. Noticed a lot of solar collector dishes on Mir-2 designs.

mir2_1.png

Edited by DDE

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Already included. Lifetime in LEO of solar power units (>20 years) is up to multiple times of e.g. a kilopower unit ("10 years or more").

 

Edited by Green Baron

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On 12/20/2018 at 11:04 AM, magnemoe said:

 

This, you nailed it, look at the types of missions we does, its small probes to various planets, people to IIS and various satellites. 
For none of this missions the LV-N in KSP is an good engine, its only relevant for heavy payloads and pretty high dV requirements or medium payloads with very high dV requirements. 

Nerva start to get relevant for manned moon missions or heavier probes who require high dV burns. Its very nice for manned mars missions. 

Exactly, our missions aren't ambitious enough to justify the development cost for nuclear engine. Even if NTR engines were available here and now without any complications such as radiation, I still don't see them to be used for what we do today: launching probes to nearest planets, asteroids and crewed LEO expeditions. The only application that I am able to find is to transfer small probes (3-6 metric tons) directly to Jupiter and Saturn without relying on gravity assists. That would require creating a small Centaur-like nuclear upper stage for Atlas rockets. But you can get around that simply by using larger rockets - SLS for instance is supposed to launch Europa Clipper directly towards the destination. Oh and we launch probes to outer planets only once per 10 years or so - it's hard to imagine developing such hardware just to be used once per decade.

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56 minutes ago, winged said:

Oh and we launch probes to outer planets only once per 10 years or so - it's hard to imagine developing such hardware just to be used once per decade.

Evidently NASA can imagine quite a bit,

56 minutes ago, winged said:

SLS for instance

P.S. Low-hanging fruit, I know.

Edited by DDE

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