On 11Oct2020 0815, Timothy Collinson - timothy.collinson at port.ac.uk
(via tml list) wrote:
> So they've come up with a scheme to fill the cargo hold with water. > Remember they already have 50 tons of collapsible fuel tanks in the
> 205 ton hold so they can make two Jump 1 jumps. Now with a cargo of >
water as well, they can refine that on the second Jump to do a > *third*
immediate Jump. > After (some considerable) calculations by the engineer
and assistant, > they decided that 99ish tons of water would be
sufficient for 52 tons > of fuel. (I have to trust them on that as I've
no idea...) Even > better, the remaining fifty tons or so of hold can be
used to store > the oxygen that they'll crack out of the water to make
the fuel. It > wouldn't even need all that space. We think. > Now
assuming the maths is correct, which I'm happy to do, I guess my >
question is: why can none of us remember this having been suggested > or
done before? Is it reasonable, or am I (are we) missing > something?
Water masses 1 tonne per cubic metre, and thus 14 tonnes per
Displacement Ton. Of this mass 1/9th is hydrogen, 8/9ths are Oxygen.
Liquid Hydrogen masses 1 tonne per Displacement Ton (by definition).
Liquid Oxygen masses 1.14 tonnes per cubic metre, and thus 15 tonnes per
Displacement Ton.
So if you crack one DTon of water (14 tonnes), you get 1.56 tonnes of
hydrogen that takes up 1.56 DTons of volume (when cooled to a liquid),
and 9.78 tonnes of oxygen that takes up 0.65 DTons of volume (when
cooled to a liquid).
The result of all this is that water is a volume efficient way of
carrying hydrogen, compared to carrying it as a pure liquid, but it has
a huge mass penalty. To get 52 tonnes of hydrogen they need 468 tonnes
of water, which takes up 33.4 DTons of space.
Ah yes, these were the numbers being thrown around and where I got the 99 DTons from. Though I now I take time to think about it they don't need the water for all three Jumps as they can presumably Jump with both regular fuel tanks full and the previously fitted collapsibles for their first two Jumps.
They'll want tanks for
this, as I doubt a normal freighter's cargo spaces are rigged for 'free'
liquid,
No, I wouldn't allow that
and nor will the holds normally have facilities for pumping it
to the refinery. They should be cheaper than fuel tanks, as water isn't
cyrogenic. They'll also want a 20 DTon tank for the oxygen, and that
will need to be a 'proper' cyrogenic one.
Yes, we remembered the oxygen, can't recall if we settled on a size. So, noted. Thank you.
(I've also noted Jim's correction from 20 DTons to 12.44 DTons or 0.78 cooled).
Fortunately Traveller ships generally care very little about the mass of
their cargo in most rule sets, only the volume.
Phew.
As for why it's not been done before - I remember variants of this
discussion way back when.
Yes, I may have read something on TML years ago that I've long since forgotten. And shame on me for forgetting the numbers above about water to hydrogen etc which I must have read on TML previously and may have even (not properly) learned at school.
Rupert wrote:
>Just dump the oxygen if you don't need it.
Although the discussion had moved on so he may not be talking about during Jump.
But we discussed this and agreed they couldn't vent oxygen during Jump.
Jim wrote:
>Not to mention it's handy for drinking, generating O2 and can even be used for CO2 scrubbing if things get really hairy...
Also not to mention scrubbing the carpets in the passenger lounge as Fred has been doing and which will be revealed when I post this week's installment.
thank you everyone once again. Sounds like the plan will work and might just possibly get them to Aramanx faster than if they just refuelled on the way. Presumably not counting any, ahem, encounters along the way.
Of course, *had* they taken up Fifth Speaker's patron request, leaving Ghazan at the Methanophiles conference (which had been the initial plan when I naively imagined he'd only be with us for one virtual session) and the March Harrier headed back to Junidy several game days back, they'd have a hold converted not to hold not hydrogen but methane and a bunch of Ebokin aboard... Something else we can blame on coranavirus. Or thank it for. Poor Jim. Did he have any idea what he was letting himself for?!
tc