In my search for ways to increase the cargo tonnage of merchant ships,
I discovered an interesting technique: Store most of the fusion plant
fuel in the form of water, and only refine it to hydrogen as needed.
Water is a more space efficient way to carry hydrogen than LH2. Since 1
kl of LH2 masses ~0.07 tons, and the mass of the hydrogen in 1 kl water
= 1/9*1 = ~0.11 tons, this results in a space savings of about 1/3.
Most ships have fuel purification plants, and since they can refine
water obtained from ocean refuelling they can certainly refine water
already in the tanks.
This tactic can be very helpful for power plant fuel, but jump fuel is
needed too fast (all burned in about 10 minutes) for the purification
plant to keep up. Since the minimum size TL 15 plant purifies 200 kl in
6 hours, it should be able to handle almost any powerplant needs. The
leftover oxygen can be dumped, used, or saved in excess tankage to
convert back to water with fuel skimmed from a gas giant. Once a ship
has entered Jumpspace, the fuel for the jump has all been used, so the
water can be refined to LH2 and LOX. I am assuming that the fuel
tankage for most ships is modular, so that you can have different fluids
in different tank sections (otherwise skimming and purifying would be
difficult). In the designs I have done, I put in a small (5-10 kl) LH2
"buffer" for the powerplant fuel, and stored the rest as water.
Hindsight makes this kind of obvious, and I think the only reason it
hasn't (to my knowledge) been noticed before is because the way an MT
manuver drive works is counterintuitive (ie only volume is important,
not mass). In any drive that depends on mass, this won't work well
since 8/9 of the mass of water is oxygen, which is useless to the
powerplant.
Any warship or explorer using this technique should probably have more
than one fuel purification plant in case one gets damaged or destroyed.
Alternatively, they could just use a buffer large enough to get the ship
back to port for repairs.
Another case where water can come in handy is for making multiple jumps
without refuelling. Only the fuel for the one jump at a time needs to
be refined, saving 1/3 the space on the fuel for all subsequent jumps.
Also if you are carrying fuel in collapsible tanks, it would seem to me
that water would be *much* safer and easier to deal with than LH2.
What to do if you are a GM and don't like this: This is kind of tough,
since the only things needed for this to work are 1) - Purification
plants can handle water, and 2) - Manuver drives don't care about mass.
The only real way to get rid of it is to axe 2), which means throwing
out all the existing official ship designs, as well as making certain
types of ships impossible to build (ie anything with heavy armor).
I'm interested in any comments or suggestions you might have.
W. Dow Rieder
When the only tool you have is a hammer, all your problems
start to look like nails...