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Broadswords into Ploughshares

Carlobrand said:
Which means there's enough water on Earth to fuel 205.3 billion squadrons.
...Our little Size 1 planet has 1/512 the volume of Earth. Our hydrographics is about 1/7 that of Earth. ...
I think I got that math right. Anyway, planets are very, very big places, and we are very, very small. If you take a 12" world globe, Plankwell is smaller than a speck of dust.
Click to expand...

Sounds true. And they've just discovered the equivalent water in an Earth underground ocean buried in the rock. Essentially, garden worlds are nice and wet. Not mentioning any other water in a garden worlds' star system.
 
I was always wondering about the effect refuling would have long term on a planet...now how about all the extra Oxy released into the atmo. Anyone have ideas on the long term effect of that? Other than stalling a carbon issue like this planet is having.

Just playing mind games here but the number crunching is useful for planning.
 
shadowcat20 said:
I was always wondering about the effect refuling would have long term on a planet...now how about all the extra Oxy released into the atmo. Anyone have ideas on the long term effect of that? Other than stalling a carbon issue like this planet is having.

Just playing mind games here but the number crunching is useful for planning.
Click to expand...

I've no idea how they figure it, but Wiki says mass of atmosphere's around 5.15 x 1018 kg. I imagine there's some wiggle room depending on how you calculate it, but that'll do for this. Means there's about 1.08 x 1018 kg of oxygen out there, the rest being nitrogen and other stuff.

To raise that O2 level 1% requires the release of 1.08 x 1016 kg of oxygen. Oxygen's most of the mass of a water molecule, so cracking about 1.22 x 1016 kg of water gives you 1.08 x 1016 kg of oxygen and 1.4 x 1015 kg of hydrogen - 1.4 trillion tons of hydrogen.

We guessed that a battle squadron needed around 750,000 dTons of hydrogen to refuel. That means you'd have to refuel a squadron 1.867 million times before the O2 went up a percent. Our hypothetical fleet of 2500 dreadnought squadrons would need to refuel 747 times to raise the O2 level 1%. Again, if we assume the fleet goes out somewhere and then comes back, refueling at Earth once a month, that's 62 years.

So, in a nutshell, you're likely to run into environmental problems from O2 release long, long, long before you run into a water shortage - and that's assuming environmental or ecological factors don't compensate to soak up some of the excess. On the other hand, you have to refuel at a ferocious rate to hit that point: 20 thousand dreadnought-sized J4 ships every month for 62 years just for a bare 1%.

Here's an interesting and only tangentially relevant fact: According to the wiki, it takes 237.13 kJ of electrical energy to dissociate each mole of water,

http://en.wikipedia.org/wiki/Water_electrolysis#Efficiency

or 13,173.889 kJ of electrical energy input to dissociate each kg (at 55.55 moles to the kg). Your 250 Mw / 1 EP power plant can crack hydrogen at a maximum rate of about 19 kg per second, probably less since the ship's using some of that energy for other things and there are always issues of efficiency of moving energy about. Anyway, figure a MAXIMUM hydrogen output of 2 kg/second, and 16 of oxygen (and we'll toss away the extra energy as busy doing something else at the moment). 500 seconds minimum to produce a dTon of hydrogen, per EP. Might be easier just to say 10 minutes per dTon per EP, take the rest of the energy as loss and energy busy with other duties and imponderables. At that rate, your Free Trader with its 30 dTon fuel tanks needs 2 1/2 hours to fuel up, sucking up 15 kg (a bit under 4 gallons) of water per second, applying 197,600 kilojoules to it per second (and we're saying the rest of your plant output is being used for something else like the pumps or the ship's lighting or something), and producing 13.33 kg of waste oxygen - please do not light matches while performing operation.

That oxygen might actually be worth something if there weren't so many other ships and services doing the same thing. On a low tech world, someplace without cheap fusion but with enough tech to make use of liquid oxygen, it might in fact be worth something. You figure if a pre-fusion O2 supply company's paying 10-20 cents a kilowatt-hour for the local energy he uses to make oxygen (a kilowatt-hour's 3.6 megajoules), you can maybe hook up with him and make a deal where you put down in his parking lot and he delivers the water and draws off your waste oxygen at 20-40 cents a kilogram, half his usual cost.
 
An remember that little moon Europa has as much water as Earth, so running out of water is not likely, and you don't need to worry about the extra 02
 
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