Why we don't see methane or ammonia-fuel starships

A thread of 2 messages, 26 April 1990 to 27 April 1990, in the order they were sent.

#1258 Why we don't see methane or ammonia-fuel starships

Ok, went home and thought about it and cranked some numbers.  Figured out why
you don't want to use different fuels.

The average starship has much if not most of its fuel volume as jump fuel.
Now, from Starship Operators Guide [yes, it's not GDW but they approved it so
i figure it's official], the Zuchai energy storage capacitors in a Jump drive
can't be held charged for more than two hours safely; three max.  Thus, the
jump powerplant must generate its power within [let's say for safety's sake]
an hour.  And it needs enough fuel to run for an hour...

Now, if we're going to purify something else on the fly, this means that we
need six times the usual purification plant [which will take 6 hours].  At
TL 15, the purification plant is 20% of the fuel volume for the 6hr version.
For our faster requirements, it rises to 120%.  This means that the total
of jump fuel volume and purification plant is now 220% of what we started
with...and even with a fuel of relative hydrogen density 1.9 we are still
16% over the volume of pure hydrogen.  You Lose...

Even if we're optomistic, and assume that we can push the two-hour lower
limit on crystal charge, we're at 160% volume, divided by 1.9 to 84% of the
origional volume.  We only gain 16%, and in the process lose reliability
[if the purif plant breaks we're stuck], safety [how long do you WANT to hold
those crystals charged???], and convenience [ya want WHAT instead of hydrogen?]
compared to hydrogen.  Plus, the added cost of the purification plant [a not
inconsiderable 150kCr/kl ] makes this a touchy option.

It is no longer the wonder-fuel.  Go home, people, and have a good night.  If
you really want to trade off the 16% for the added headache i won't mind if
I'm GMing, but i warned ya what's going to go wrong :-)

*******************************************************************************
George William Herbert              JOAT For Hire: Anything, Anywhere: My Price
   UCB Naval Architecture undergrad: Engineering with a Bouyant Attitude :-)
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"Who?" the man managed.                    Whip me, Beat Me, Make me learn C...
"The Rastafarian Navy," Case said,         ++++++++++ [email removed]       OR
"...and all we want is a jack into your    ========== [email removed] OR
custodial system." -neuromancer            """""""" [email removed]

#1264 Re: Alternative Fuel Storage

[I changed the subject line to be more meaningful -- James]

George William Herbert writes:
>Ok, went home and thought about it and cranked some numbers.  Figured out why
>you don't want to use different fuels.
[shows why you need LH2 for jump fuel]

Quite true. I did a similar analysis. I think that in my original
posting it was
stated that the method wouldn't work for jump fuel.

>The average starship has much if not most of its fuel volume as jump fuel.

That depends.  A scoutship has jump-2 and, if memory serves, a 864Mw
powerplant.  It needs 202.5 kl of jump fuel, and 311.04 kl to power the
fusion plant for a month.  Storing the power plant fuel as water would
save about 100 kl, which would more than triple the cargo capacity.
	Any ship with a purification plant must have segmented fuel
capacity, so storing some fuel as water and some as LH2 works. (although
you probably want to adjust the temperature in a segment before
switching fuel types :-)

					W. Dow Rieder

 	When the only tool you have is a hammer, all your problems
start to look like nails...