Nuclear ground-orbit vehicle

[raniE]

Originally Posted by tratclif

According to Aerospace Projects Review V2 N1, the engine designers were never able to prevent the engine elements from eroding off dust-to-sand-size particles, so the Pluto would have left a "noticeable" radioactive trail.

Can one assume that such problems would be fixable? Using TL9 fission technology that is.

[malloyd]

Originally Posted by raniE

Can one assume that such problems would be fixable? Using TL9 fission technology that is.

I'm sure they are. One possible solution for some versions of TL9 is coat the entire air passage in diamond layer. That's not going to abrade off easily, and carbon doesn't neutron activate easily anyway.

[DAT]

In the 90’s I had heard we were looking at some cutting edge ‘solid’ core Nuclear Rockets with engine power densities in the range of one hundred mega-watts per liter. I haven’t calculated the specific impulses for one, but they should be decently high.

Assuming 100MW/l for an average TL9 Nuclear Rocket, with those power densities, some of the hydrogen fuel would be activated as it passed through the core and you would end up with a fair amount of tritium in the exhaust. Between the very intense neutron fluxes and the local gamma-heating with the resulting embrittlement and differential thermal expansion, any known or currently forecasted coating you cared to try would take a beating. So I would say you should assume a few fission products and activation products in your exhaust would be likely.

But if you want to assume a significant improvement in materials sciences for TL9, say a very high temperature metallic glass coating or a variation of the diamond coating, you could limit your radiation source to the tritium from the activated hydrogen fuel.

[theshadow99]

Originally Posted by DAT

Assuming 100MW/l for an average TL9 Nuclear Rocket, with those power densities, some of the hydrogen fuel would be activated as it passed through the core and you would end up with a fair amount of tritium in the exhaust. Between the very intense neutron fluxes and the local gamma-heating with the resulting embrittlement and differential thermal expansion, any known or currently forecasted coating you cared to try would take a beating. So I would say you should assume a few fission products and activation products in your exhaust would be likely.

If not TL 9... TL 10 with it's nanotechnologies should be able to adapt a carbon regenerating sheath to use inside... Now a TL 9 Rocket Engine could be built using a TL 10 tech... It would just be really expensive...

[raniE]

Originally Posted by DAT

In the 90’s I had heard we were looking at some cutting edge ‘solid’ core Nuclear Rockets with engine power densities in the range of one hundred mega-watts per liter. I haven’t calculated the specific impulses for one, but they should be decently high.

Assuming 100MW/l for an average TL9 Nuclear Rocket, with those power densities, some of the hydrogen fuel would be activated as it passed through the core and you would end up with a fair amount of tritium in the exhaust. Between the very intense neutron fluxes and the local gamma-heating with the resulting embrittlement and differential thermal expansion, any known or currently forecasted coating you cared to try would take a beating. So I would say you should assume a few fission products and activation products in your exhaust would be likely.

But if you want to assume a significant improvement in materials sciences for TL9, say a very high temperature metallic glass coating or a variation of the diamond coating, you could limit your radiation source to the tritium from the activated hydrogen fuel.

You say hydrogen fuel here, are you talking about the reaction mass? Because there is going to be no pure hydrogen remass in the design. The engines use either air (in the atmosphere) or water (when the air becomes too thin). How would this affect fallout levels?

[Fred Brackin]

Originally Posted by raniE

You say hydrogen fuel here, are you talking about the reaction mass? Because there is going to be no pure hydrogen remass in the design. The engines use either air (in the atmosphere) or water (when the air becomes too thin). How would this affect fallout levels?

Hydrogen reaction mass is often assumed because it gives the highest ISP. Technically it is the fissionable material that is the fuel.

Basically it is only the fissionables that would be a significant source of fallout. Neutron bombardment of either hydrogen alone or in combination with oxygen or again O2 combined with N2 and a little CO2 does not produce significant amount of radioactive isotopes. All of the common isotopes of these elements plus one neutron produce still stable nuclei. Only the relatively rare deuterium would become tritium when hit with a neutron. Even the tritium is not a terrible radioactive threat.

Also, unlike the heavy radioactives, even the tritium vapor has no particular tendency to fall to Earth eventually. Even extra-heavy hydrogen is still lighter than air.

Neutron bombardment of the engine parts could produce some undesirable substances to go along with the fission fuel and fissioned fragments.

[raniE]

Originally Posted by Fred Brackin

Hydrogen reaction mass is often assumed because it gives the highest ISP. Technically it is the fissionable material that is the fuel.

I know, which is why the mention hydrogen as fuel threw me off. Also, I did mention earlier my plans to use water as the reaction mass due to it's cheapness.

Originally Posted by Fred Brackin

Basically it is only the fissionables that would be a significant source of fallout. Neutron bombardment of either hydrogen alone or in combination with oxygen or again O2 combined with N2 and a little CO2 does not produce significant amount of radioactive isotopes. All of the common isotopes of these elements plus one neutron produce still stable nuclei. Only the relatively rare deuterium would become tritium when hit with a neutron. Even the tritium is not a terrible radioactive threat.

Also, unlike the heavy radioactives, even the tritium vapor has no particular tendency to fall to Earth eventually. Even extra-heavy hydrogen is still lighter than air.

Neutron bombardment of the engine parts could produce some undesirable substances to go along with the fission fuel and fissioned fragments.

So, assuming TL9 technology, it's perfectly feasible to assume minimal levels of radioactive fallout from the engine?

[Fred Brackin]

Originally Posted by raniE

So, assuming TL9 technology, it's perfectly feasible to assume minimal levels of radioactive fallout from the engine?

Yes.The fuel can be contained and bits of the engine can be kept from falling off.

[raniE]

Originally Posted by Fred Brackin

Yes.The fuel can be contained and bits of the engine can be kept from falling off.

Do you think anyone would go for nuclear powered spaceplanes though? Or would the fear of catastrophic failure put a stop to any such plans?

[Langy]

Depends on the politics of the setting. I don't even have the first idea if people would accept it or reject it right now.