Attacking Darius:

cthia wrote:

ThinksMarkedly wrote:On the momentum transfer side, in one hour, that ship gained 900 billion kg m/s of momentum. If the hydrogen was expelled out at 0.1c relative, then the ship must have pushed out 30 tonnes in one hour. I suppose it can send 28 t of hydrogen and 2 tonnes of helium that is the product of fusion, so it keeps its bunkerage expenditure at 30 t/hour. Those are belieavable numbers.

Loren Pechtel wrote:Yeah, you're right, it's a mix of hydrogen and helium, not just hydrogen. Might as well use the waste helium from the reactor as reaction mass.

I suppose that would be a win win situation. Recycling waste hydrogen by finding a use for it. But hydrogen is very flammable, and the reactors of the large ships of the wall are buried deep inside the bowels of the ship, iinm. At any rate, you have very hot plasma coursing thru the veins of the ship, along with veins of hydrogen. I can't believe even a single hit from a graser head doesn't cause even an SD to flame like data. A pipe leading from the reactor's hydrogen containment to the thrusters on the hull of the ship sounds like a very long fuse on a huge stick of dynamite. HV ships should be more flammable than the Hindenburg. And I don't care how much armor an SD has, explosions emanating from the inside are much more fatal.

Another hypothesis comes to mind that explains how it could be as dramatic as the quoted text says:

The thrusters are fed liquid hydrogen and use gravitic fields to cause it to fuse. This gets around much of the waste heat problem, the ship is never trying to handle that much energy.

kzt wrote:No, you’d store it as water. Liquid hydrogen is terrible. It’s a cryo fluid, it’s extremely low density. It it warms up it, to say 25 kelvin, it expands like 700 times. So now you have an expanding cloud of supercold gas that can penetrate virtually any seal turning your ship into a fragile glass carving.

The energy needed to disassociate water is trivial if you are feeding into a fusion reactor.

Good point. And water isn't combustible in the first place because it's already oxidised. A laser being going through it would cause vaporisation and probably the electrolysis, but it's localised.

ThinksMarkedly wrote:
Good point. And water isn't combustible in the first place because it's already oxidised. A laser being going through it would cause vaporisation and probably the electrolysis, but it's localised.

You'd get a huge shockwave in it with a HEL passing through it. I think you'd also get that with liquid hydrogen, but not sure if liquid hydrogen is compressible, so it might be less of an effect. However it doesn't take a lot of heat to heat up cryo fluids, and the expansion as it turns to gaseous hydrogen is on the order of 700 times.

There are some materials that are still pretty strong at cryo temperatures, so it you avoid using things that have a brittle transition so I think you could have tanks for water or liquid hydrogen that are comparable in strength.

But I just don't see any compelling reason to store huge volumes of liquid hydrogen. You could use it as a heat sink, but you can also cool water ice to 10 Kelvin too and it makes a fine heat sink.

ThinksMarkedly wrote:Good point. And water isn't combustible in the first place because it's already oxidised. A laser being going through it would cause vaporisation and probably the electrolysis, but it's localised.

kzt wrote:You'd get a huge shockwave in it with a HEL passing through it. I think you'd also get that with liquid hydrogen, but not sure if liquid hydrogen is compressible, so it might be less of an effect. However it doesn't take a lot of heat to heat up cryo fluids, and the expansion as it turns to gaseous hydrogen is on the order of 700 times.

There are some materials that are still pretty strong at cryo temperatures, so it you avoid using things that have a brittle transition so I think you could have tanks for water or liquid hydrogen that are comparable in strength.

But I just don't see any compelling reason to store huge volumes of liquid hydrogen. You could use it as a heat sink, but you can also cool water ice to 10 Kelvin too and it makes a fine heat sink.

You can get the cooling for free by giving the water tanks heat radiators into space. Provided your waste heat has peaks and valleys, the water tank should do a very good job of averaging the fluctuations out. The tank needs to be designed to handle the fact that water expands as it freezes; they need to handle that pressure.

I thought when people discussed using hydrogen to power a car that they considered metal hydrides to store the gas in a more compact form. I assume that there must be problems with this?

I am a civil engineer. Using water to create hydrogen is brilliant. The prohibiting factor for using electrolysis to create hydrogen has ways been the cost.

Due to conservation of energy the energy that is used for the conversion exceeds the energy produced by the hydrogen. And because systems are not perfect, it exceeds the energy produced.

But as kzt noted, since you are feeding water to a reactor anyway, that problem is solved. However, the reason I noted that I am an engineer is because I look at things as they are in real life, and I immediately consider the logistics of such an operation. I worked for a while in municipal water supply, for cities. Immediately upon this discussion I entertain the variables of influent and effluent flow of the water system, and the relief valves and the overflow system.

This consideration leads to the consideration of the proper location for the water. Will pumps be used to feed the water to the reactor? If so, pumps are a point of failure. Will gravity be used to feed the water (water higher in elevation than the reactor) which is unreliable on a warship. Pressure? Also problems to solve. But I think these things are solvable in the HV.

But then there is the logistics of the system. Is the bunkerage stored near the skin of the ship? Where is the "gas tank" located on the ship? That is one of the first things you need to know when you purchase a new car. Where does the nozzle go when you want to fill her up?

If the bunkerage is stored near the skin of the ship it has a long travel to the reactor, converted into hydrogen and back out to the thrusters located on the skin of the ship. The bunkerage can be kept deep in the bowels of the ship nearer the reactor, but the hydrogen produced still has to travel the long distance to the reactor.

There will always be at least one long vein of highly combustible hydrogen coursing through the ship. Which brings us right back around to my notion of the one long fuse leading to a stick of dynamite. Which leads right back to the reactor.

I am a civil engineer. Using water to create hydrogen is brilliant. The prohibiting factor for using electrolysis to create hydrogen has ways been the cost.

Due to conservation of energy the energy that is used for the conversion exceeds the energy produced by the hydrogen. And because systems are not perfect, it exceeds the energy produced.

But as kzt noted, since you are feeding water to a reactor anyway, that problem is solved. However, the reason I noted that I am an engineer is because I look at things as they are in real life, and I immediately consider the logistics of such an operation. I worked for a while in municipal water supply, for cities. Immediately upon this discussion I entertain the variables of influent and effluent flow of the water system, and the relief valves and the overflow system.

This consideration leads to the consideration of the proper location for the water. Will pumps be used to feed the water to the reactor? If so, pumps are a point of failure. Will gravity be used to feed the water (water higher in elevation than the reactor) which is unreliable on a warship. Pressure? Also problems to solve. But I think these things are solvable in the HV.

But then there is the logistics of the system. Is the bunkerage stored near the skin of the ship? Where is the "gas tank" located on the ship? That is one of the first things you need to know when you purchase a new car. Where does the nozzle go when you want to fill her up?

If the bunkerage is stored near the skin of the ship it has a long travel to the reactor, converted into hydrogen and back out to the thrusters located on the skin of the ship. The bunkerage can be kept deep in the bowels of the ship nearer the reactor, but the hydrogen produced still has to travel the long distance to the reactor.

There will always be at least one long vein of highly combustible hydrogen coursing through the ship. Which brings us right back around to my notion of the one long fuse leading to a stick of dynamite. Which leads right back to the reactor.

cthia wrote:If the bunkerage is stored near the skin of the ship it has a long travel to the reactor, converted into hydrogen and back out to the thrusters located on the skin of the ship. The bunkerage can be kept deep in the bowels of the ship nearer the reactor, but the hydrogen produced still has to travel the long distance to the reactor.

There will always be at least one long vein of highly combustible hydrogen coursing through the ship. Which brings us right back around to my notion of the one long fuse leading to a stick of dynamite. Which leads right back to the reactor.

I'd expect that you'd have the HV equiv of a day tank next to each reactor, deep inside the core armor.

Given that HV ships have plasma pipes running all over, full of stellar core plasma - say 50 million degree plasma at thousands of bar, the threat of a leak of liquid hydrogen in the reactor room just isn't a big deal.

cthia wrote:If the bunkerage is stored near the skin of the ship it has a long travel to the reactor, converted into hydrogen and back out to the thrusters located on the skin of the ship. The bunkerage can be kept deep in the bowels of the ship nearer the reactor, but the hydrogen produced still has to travel the long distance to the reactor.

There will always be at least one long vein of highly combustible hydrogen coursing through the ship. Which brings us right back around to my notion of the one long fuse leading to a stick of dynamite. Which leads right back to the reactor.

kzt wrote:I'd expect that you'd have the HV equiv of a day tank next to each reactor, deep inside the core armor.

Given that HV ships have plasma pipes running all over, full of stellar core plasma - say 50 million degree plasma at thousands of bar, the threat of a leak of liquid hydrogen in the reactor room just isn't a big deal.

It is also possible (as someone else has already said), that the thrusters turn water into plasma; therefore no long pipes containing hydrogen.

tlb wrote:It is also possible (as someone else has already said), that the thrusters turn water into plasma; therefore no long pipes containing hydrogen.

You need a plasma feed into the magazines and to each energy weapon.

tlb wrote:It is also possible (as someone else has already said), that the thrusters turn water into plasma; therefore no long pipes containing hydrogen.

kzt wrote:You need a plasma feed into the magazines and to each energy weapon.

Certainly, but someone was most concerned about hydrogen exploding.

I had not realized before, but each energy weapon (on any ship) also has a plasma capacitor to smooth out energy peaks. A graser uses more energy then could be supplied from the reactor for each shot, so it depends on the capacitor recharging.