13.5 or 14?

[Andrew Boulton]

The broken file is fixed.

 

[tjoneslo]

Originally posted by Uncle Bob:
14.124 m3/ton is the proper volime for liquid hydrogen. Assuming 5% by mass for insulated tankage for long-tem storage gives you 13.5 m3/tons, which works well for deckplans. Works for me.

Just to make everyone's life more interesting. NASA was playing with their Liquid Hydrogen and found if you apply pressure, then release it, the pressure release causes crystals to form. By using a 50% slurry of crystalized LHydr and normal Liquid Hydrogen, you can reduce the density to around 11 m3/ton. The slurry can be stored in the same tanks as normal LHyd, and has exactly the same performance in their rocket engines.

Of course, the real reason for the DTon being based upon liquid hydrogen is because GDW designers wanted a simple way of marking deck plan sizes. 1 Dton = 2 1.5m squares on the deckplans. Makes ships easy to figure, design and draw.

 

[DED]

Originally posted by TheDS:
Which displacement ton do you prefer?

13.5 kl is the value used in CT and MT. It has the advantages of being previously established, and also of being the correct value.

14 kl is the value used in TNE and T4. It seems to be well accepted, and is easier to punch into the calculator.

13.5


I hated the fact that TNE went down to 2 significant figures. As someone else already pointed out, FF&S is already so complicated you can't hope to build anything without using a spreadsheet, much less a calculator, why not go for the accuracy of 3 significant figures. That extra 0.5 goes a long way.

 

[Uncle Bob]

Originally posted by kaladorn:
</font><blockquote>quote:</font><hr />Originally posted by Uncle Bob:
An exquisite proof, but flawed somehow.
The density of LH2 is 70.8 Kg/m3 at 20.28 K
http://www.efunda.com/materials/elements/element_info.cfm?Element_ID=H

Accept my 5% tankage, it made life easier for me and it can do the same for you.

Hmmm. Unfortunately, that only argues for 14, if true. Because a lot of the ship is NOT fuel tanks and it uses the same displacement for a ton.

Then again, the Imperial standard for a ton may have somehow changed such that it really is 13.5 by that time period.... </font>[/QUOTE]I say again, LH2 is 14.124 m3/ton. It just is, and talking won't change that.


But the standard of Traveller is not liquid hydrogen, but LH2 in ten-ton storage tanks.
Allowing 5% of the "hydogen" mass to tank walls and support structure you get 9.5 tons of LH2 and 0.5 tons of aluminum you get 134.1 m3 of LH2 plus 0.2 m3 of Aluminum plus 0.7 m3 of insulating voids in the tank walls gives 135 m3.

That is 13.5 m3/ton for hydrogen and tanks.

The rest of the ship doen't have to be divided up the same way, this just establishes the standard density.

 

[TheDS]

Sounds like it's time to ask Avery....

 

[Avery]

There is an obscure reference (now long forgotten by me, or lost) that Lanthanum functions as a sponge for Hydrogen, holding a greater volume than liquid hydrogen.

I remember only that that reference, unchecked in the days before internet research, prompted the selection of Lanthanum as the material ofimportance for jump drives.

 

[kaladorn]

Originally posted by Uncle Bob:
I say again, LH2 is 14.124 m3/ton. It just is, and talking won't change that.

Unequivocal, but also historically speaking untrue.

Over the years, the definition of what constitutes a particular unit of measure (and I'm not talking about changing units of measure, but changing the exact definition of a unit of measure, thus slightly changing its value) have occured many times.

At one point, a meter had one definition. Now it is defined in an entirely other matter. I think seconds may have changes too.

So it is possible, though admittedly quite unlikely, that the definition of what a 'ton' is, in your example, or a 'cubic meter' will have changed. So if I change what the units mean, I change what valuation I'm likely to end up with, thus the size of a 'ton' (whatever that is at the time... once upon a time when you said ton you had people think of 2000 lbs, now tons often mean about 2200 lbs. -- though they've stuck in different spellings to help people differentiate a metric and imperial ton) of displacement may actually NOT be the same.

As I concede, this isn't likely, but 3500 years is a pretty darn long time.

 

[TheDS]

Well, I went and asked Avery, but he had just answered a vaguely similar question (which I didn't notice until after asking), and might decide it's the same thing (which it isn't) and therefore not answer it.

AAAnyhow... Tonnage, as far as I know, has always been the volume of 1 tonne of LHyd. Whether that's 13.5, 14, 14.124, 11, or whatever, we must remember that the stuff of importance is LHyd. Gelling or slushing or crystalizing, while probably the storage medium of the future, is not what this measurement is based on.

By allowing the GM to specify what he wants to call a Dton, and making sure he knows what his choices are, will still work. It would be nice to know why 13.5 and 14 have been used, but it's not absolutely critical, I guess.

Thank you all for your input on this matter; I hope we've all learned something, and that if anyone else has anything to contribute, they will feel free to do so.