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18 hours ago, Bill Phil said:

NPP doesn't have to be purely fission... Pure fusion bombs, if possible would be NPP as well. Plus, we have bombs that are almost 98% fusion. Wity only 2% of the yield being from fission. Not to mention that the linear no threshold model isn't considered rob be the best these days.

Illegal is a bit of a stretch. It can be used if any nation wants to...

Ummm.... no. Pure Fusion bombs do not exist.

Also, they don't scale linerarly, and NPP would tend to use smaller detonations, which means the % from fusion goes down.

The Russian "Tsar bomba" was one of the "cleanest" (maybe the cleanest) bombs built, with 97% of its energy coming from fusion, not fission. It was also the most powerful explosive ever built and utterly unsuited for NPP propulsion.

Oh, and by the way, that single bomb released 25% of the fallout from all nuclear weapons testing combined.

https://en.wikipedia.org/wiki/Tsar_Bomba

So... No...

However getting to orbit with a nice NTR like this:

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

late 80's/early 90's technology was getting 890s *sea level* Isp and 1000s vacuum Isp, with a 30:1 TWR... that sort of technology can SSTO fairly easily, and from there you can go with NPP

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2 hours ago, KerikBalm said:

Ummm.... no. Pure Fusion bombs do not exist.

Also, they don't scale linerarly, and NPP would tend to use smaller detonations, which means the % from fusion goes down.

The Russian "Tsar bomba" was one of the "cleanest" (maybe the cleanest) bombs built, with 97% of its energy coming from fusion, not fission. It was also the most powerful explosive ever built and utterly unsuited for NPP propulsion.

Oh, and by the way, that single bomb released 25% of the fallout from all nuclear weapons testing combined.

https://en.wikipedia.org/wiki/Tsar_Bomba

So... No...

However getting to orbit with a nice NTR like this:

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

late 80's/early 90's technology was getting 890s *sea level* Isp and 1000s vacuum Isp, with a 30:1 TWR... that sort of technology can SSTO fairly easily, and from there you can go with NPP

Pure fusion bombs don't exist yet, yes. But they likely could be built eventually.

I know very well that it doesn't scale linearly. But wity enough effort it could be done.

Who says the Tsar Bomba is unsuited for NPP? Yeah it's yield is huge, but that means that it has loads of energy. And since NPP is scalable to huge scales, a bomb with its yield could be used.

It released 25% of the fallout for a variety of reasons (and I doubt that figure, as I was unable to find it in your link), and that's not related to the discussion at hand. Even if the percentage is only 50%, which could be possible, but inefficient, the nuclear fallout would be diminished.If you can get it to the stratosphere before you light it, then the fallout would be diluted.

If they have that miracle tech than why would they not use it? Maybe it's because it was only a study.

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The same reason we don't have nuclear powered ion drive vessels... also related to why the old NERVA never flew.

Sending nuclear reactors to space is very risky and unpopular.

Its also related to issues the skylon faces... its only going to pay off if you have a massive launch rate.

The Timberwind engines are somewhat analogous to the Sabre engine. Its an awesome engine design... but the complete engien hasn't actually been built - but everything suggests it could be built. Then once the engine is built, you need to design a spacecraft for the engine... a reusable spacecraft otherwise there isn't much point in doing it... although for NTRs use in upper stages is considered, with re-use without deorbiting also considered.

As an upper stage engine... it doesn't really have any use beyond sending massive payloads to the moon or interplanetary... and we're nowhere near ready for a massive mars colony or moon base... so what would they do with the engine if they had built the design?

... and that is why they didn't build it.

FWIW, 1000s is not a miracle tech.... The TWR is the most impressive statistic relative to the older NERVA.

I highly doubt pure fusion bombs will be built... no we're talking miracle tech.

I was mistaken about the 25% of all fallout... that was an estimate for what would have resulted if they had tested the 100 MT design with a fission 3rd stage.

"It has been estimated that detonating the original 100 Mt design would have released fallout amounting to about 25% of all fallout emitted since the invention of nuclear weapons."

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36 minutes ago, KerikBalm said:

The same reason we don't have nuclear powered ion drive vessels... also related to why the old NERVA never flew.

Sending nuclear reactors to space is very risky and unpopular.

Its also related to issues the skylon faces... its only going to pay off if you have a massive launch rate.

The Timberwind engines are somewhat analogous to the Sabre engine. Its an awesome engine design... but the complete engien hasn't actually been built - but everything suggests it could be built. Then once the engine is built, you need to design a spacecraft for the engine... a reusable spacecraft otherwise there isn't much point in doing it... although for NTRs use in upper stages is considered, with re-use without deorbiting also considered.

As an upper stage engine... it doesn't really have any use beyond sending massive payloads to the moon or interplanetary... and we're nowhere near ready for a massive mars colony or moon base... so what would they do with the engine if they had built the design?

... and that is why they didn't build it.

FWIW, 1000s is not a miracle tech.... The TWR is the most impressive statistic relative to the older NERVA.

I highly doubt pure fusion bombs will be built... no we're talking miracle tech.

I was mistaken about the 25% of all fallout... that was an estimate for what would have resulted if they had tested the 100 MT design with a fission 3rd stage.

"It has been estimated that detonating the original 100 Mt design would have released fallout amounting to about 25% of all fallout emitted since the invention of nuclear weapons."

A sea level ISP of 890s means that  a mass ratio of 3 would be all you need to orbit. Less if you take into account the vac ISP. That's miracle tech. Now, miracle tech does not equal impossible. 

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Hmmm, never bothered to do the math on it.

Mass ratio of 3 indeed... even a bit lower. TWR of 30. Lets assume launch is limited to 4 Gs as with the shuttle IIRC.

30/4 = 7.5    So the whole rocket can be 7.5x the mass of the engine. Wet:Dry must be 3:1... so that suggests a dry mass of 2.5x the engine mass.

The shuttle massed 68.6 tons, of which abotu 10.5 tons was engine.

IIRC from previous estimates, the shuttle's LH2 tank had a mass ratio of around 8:1. If the fuel is 3x the dry weight, then the fuel tanks should be about about 37.5% of the dry weight.

So the dry weight we have.... 1 Engine mass + fuel tanks (0.375*2.5) = 0.9375 Engine masses... we've only got 0.5 engine masses to go for the payload and any remaining structure for reentry or whatever... sounds pretty tight...

Or we accept an acceleration of less than 4 G's off the pad. At 2 Gs, the entire rocket can be 15x the engine mass, and thus the dry mass can be 5x the engine mass. Fuel tanks then come out to about 2 engine masses.. leaving 2 engine masses to go for structure and payload... much better than the 0.5 before.

2 G's on the pad will probably be enough, as the TWR will go up significantly as the rocket edxpends propellant

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54 minutes ago, KerikBalm said:

The same reason we don't have nuclear powered ion drive vessels... also related to why the old NERVA never flew.

Sending nuclear reactors to space is very risky and unpopular.

Its also related to issues the skylon faces... its only going to pay off if you have a massive launch rate.

The Timberwind engines are somewhat analogous to the Sabre engine. Its an awesome engine design... but the complete engien hasn't actually been built - but everything suggests it could be built. Then once the engine is built, you need to design a spacecraft for the engine... a reusable spacecraft otherwise there isn't much point in doing it... although for NTRs use in upper stages is considered, with re-use without deorbiting also considered.

As an upper stage engine... it doesn't really have any use beyond sending massive payloads to the moon or interplanetary... and we're nowhere near ready for a massive mars colony or moon base... so what would they do with the engine if they had built the design?

... and that is why they didn't build it.

FWIW, 1000s is not a miracle tech.... The TWR is the most impressive statistic relative to the older NERVA.

I highly doubt pure fusion bombs will be built... no we're talking miracle tech.

I was mistaken about the 25% of all fallout... that was an estimate for what would have resulted if they had tested the 100 MT design with a fission 3rd stage.

"It has been estimated that detonating the original 100 Mt design would have released fallout amounting to about 25% of all fallout emitted since the invention of nuclear weapons."

The lack of heavy payloads who require lots of dV is the main reason why nobody has used an nerva, 
Now add development cost for an rarely used system and its get cheaper to use an larger launcher or scale down the mission. 
Nuclear scare is an issue but probably less than the two above issues and pretty irrelevant for Russia or China.

Nuclear bombs generate more fallout than the fusion stage, you probably get some just from the air, if the fireball touch ground you get lots of fallout, this will be hard to avoid with an 100 megaton bomb. 

Now some of the current fusion rocket engine ideas is pretty cool. they generate pure fusion, no they don't have the insane trust of an orion but that trust is overkill unless you are moving an battleship or asteroid. its an engine not an reactor so you need to power it 

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