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PostPosted: Tue Oct 19, 2010 6:44 pm 
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EDG wrote:
DFW wrote:
Also, it exists in the upper atmosphere of gas giants in the form of ice. EASY skimming.


For certain values of "easy", depending on whether you want to be going in and out of a huge gravity well (this is another thing that Traveller skims over, no pun intended) :).

Methane might be another storage option?


Actually, "huge" part is tidal. The surface gravity of Jupiter is only ~2.5Gs so not a problem for ships with at least 1G continuous thrust drives.

Methane is a choice also but, it has to kept @~-162C. I forget how much Hy it contains vs. LHy though. But, it is more than straight LHy for sure. It is very combustible as you already know.

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PostPosted: Tue Oct 19, 2010 7:28 pm 
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The gravity felt by one end of a ship is still going to be pretty much the same as the gravity at the other end, so tidal forces won't be a problem (it is a problem at black holes and neutron stars though, where the gravitational strength can be significantly higher over a difference of a few metres).

The main problems are going to be frictional heating and turbulence that result from ploughing through a gas giant atmosphere at high speed. That and being able to escape the gravity well.

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PostPosted: Tue Oct 19, 2010 7:31 pm 
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DFW wrote:
Methane is a choice also but, it has to kept @~-162C. I forget how much Hy it contains vs. LHy though. But, it is more than straight LHy for sure. It is very combustible as you already know.


I'm not sure how the hydrogen is supposed to be stored in Traveller - is it cooled to liquid state or compressed?
Either way, if "combustible" is a problem then every ship should explode when it's hit in combat, given that the fuel always seems to be stored on the outside of the ship. First time anyone blows a hole through that, the hydrogen can leak explosively into the crew compartments, and detonate in the oxygen atmosphere.

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PostPosted: Tue Oct 19, 2010 7:57 pm 
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EDG wrote:
The main problems are going to be frictional heating and turbulence that result from ploughing through a gas giant atmosphere at high speed. That and being able to escape the gravity well.



Ship hulls are designed to take it. The gravity isn't high enough to present any problem for a Trav ship as it is only twice that of Earth.

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PostPosted: Tue Oct 19, 2010 8:01 pm 
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EDG wrote:
I'm not sure how the hydrogen is supposed to be stored in Traveller - is it cooled to liquid state or compressed?
Either way, if "combustible" is a problem then every ship should explode when it's hit in combat, given that the fuel always seems to be stored on the outside of the ship. First time anyone blows a hole through that, the hydrogen can leak explosively into the crew compartments, and detonate in the oxygen atmosphere.


In Trav is it liquid (VERY, VERY cold). When a ship gets an external hit to a fuel tank it can't explode as there in no oxygen in outer space. During combat it is a good idea to decompress the ship for the reason you cite above.

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PostPosted: Sun Nov 14, 2010 2:10 pm 
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DFW wrote:
So as an example; a second J1 takes 20 tons of hydrogen fuel. If you are carrying ammonia in the collapsible tank you only need to carry 11.6 tons.

That's displacement tons, of course. Liquid ammonia is much denser than liquid hydrogen, and the quantity that can be processed to extract 20 tons of hydrogen actually masses over 113 tons. When you process it you get 20 tons (mass) of hydrogen and 93+ tons of nitrogen.

We looked into this on the Traveller forum at SJGames back in February '08. Of the forms in which to store hydrogen which anyone came up with over there, the one that got the most hydrogen into a given volume was metallic hydrogen, which (assuming that it can be made and stored) would theoretically squeeze somewhere between 11 and 60 times as much hydrogen into a given space and with no mass overhead. But there's no evidence that it is available in teh Traveller universe.

Confining ourselves to materials actually existing, the most compact form for storing hydrogen anyone found was ammonium bifluoride, which is 1.87 times as compact as liquid hydrogen. (But it is 11.3 times as massive per unit hydrogen, and is a bit of a chemical nightmare.) The solution I liked best was a 1:2 molar mixture of lithium amide and lithium nitride, which is safe to handle, 1.85 times as compact as liquid hydrogen, and yields up its hydrogen on simple heating. It is 9.7 times as massive as the hydrogen it includes.

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PostPosted: Sun Nov 14, 2010 5:29 pm 
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Agemegos wrote:
DFW wrote:
So as an example; a second J1 takes 20 tons of hydrogen fuel. If you are carrying ammonia in the collapsible tank you only need to carry 11.6 tons.

That's displacement tons, of course. Liquid ammonia is much denser than liquid hydrogen, and the quantity that can be processed to extract 20 tons of hydrogen actually masses over 113 tons. When you process it you get 20 tons (mass) of hydrogen and 93+ tons of nitrogen.

We looked into this on the Traveller forum at SJGames back in February '08. Of the forms in which to store hydrogen which anyone came up with over there, the one that got the most hydrogen into a given volume was metallic hydrogen, which (assuming that it can be made and stored) would theoretically squeeze somewhere between 11 and 60 times as much hydrogen into a given space and with no mass overhead. But there's no evidence that it is available in teh Traveller universe.

Confining ourselves to materials actually existing, the most compact form for storing hydrogen anyone found was ammonium bifluoride, which is 1.87 times as compact as liquid hydrogen. (But it is 11.3 times as massive per unit hydrogen, and is a bit of a chemical nightmare.) The solution I liked best was a 1:2 molar mixture of lithium amide and lithium nitride, which is safe to handle, 1.85 times as compact as liquid hydrogen, and yields up its hydrogen on simple heating. It is 9.7 times as massive as the hydrogen it includes.


Very good. However, you aren't going to be skimming those compounds from a GG and they would be more expensive.

Not sure about you point on ammonia. You just dump the N overboard during processing.

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PostPosted: Sun Nov 14, 2010 7:50 pm 
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DFW wrote:
However, you aren't going to be skimming those compounds from a GG and they would be more expensive.

That's the beauty of the lithium amide-lithium hydride mixture. You keep lithium nitride in a tank, as a fine powder. You pump in hydrogen, and at room temperature the lithium nitride reacts with the hydrogen to produce a mixture of lithium amide and lithium hydride (both solids). When you want to use the hydrogen, you heat the tank to 270 C. The lithium amide and lithium hydride react to release the hydrogen and leave lithium nitride powder in the tank (to be used again another time).

The fact that you can't skim lithium amide and lithium hydride doesn't matter: you skim hydrogen, and pump it into the tank with your lithium nitride to store it compactly. The fact that lithium nitride isn't free doesn't matter much: you keep it and reuse it.

And besides being compact, this has the advantage that it is stable at room temperature (though it does have to be kept dry). By contrast ammonia boils at -33 C (so it has to be kept either under pressure or rather cold).

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PostPosted: Sun Nov 14, 2010 9:14 pm 
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The Li compounds take up space though don't they? If half your tank is filled with those compounds, won't that reduce the volume of hydrogen you can store in that volume?

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PostPosted: Sun Nov 14, 2010 10:05 pm 
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EDG wrote:
The Li compounds take up space though don't they? If half your tank is filled with those compounds, won't that reduce the volume of hydrogen you can store in that volume?

No, it's the same case as with ammonia. The compounds are so much denser than liquid hydrogen that you get more hydrogen into the space in question despite the presence of other elements.

Liquid hydrogen is a very low-density liquid. Its density is only 71 kg/m^3.

Liquid ammonia at -33 C is only 3/17 hydrogen by mass, but its density is 682 kg/m^3, which for the trouble of decomposing it gives you 120 kg of hydrogen per cubic metre.

A 1:2 molar mixture of lithium amide and lithium hydride is 4/39 hydrogen by mass, but its density is 1,277 kg/m^3, which for the trouble of heating it to 270 C gives you 131 kg of hydrogen per cubic metre. After you heat it your tank is indeed still "full" of lithium nitride powder (1,146 kg/m^3 of it), but if you pump in hydrogen and keep it cool the hydrogen will react with the lithium nitride and restore your reserves.

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Last edited by Agemegos on Thu Sep 01, 2011 10:44 pm, edited 1 time in total.

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