[Heresy] Tons of Fun

[thrash]

Classic Traveller suffers a bit of confusion over what is meant by a "ton." From Book 2 (1981):

Originally Posted by p. 13

The Hull: Hulls are identified by their mass displacement, expressed in tons. As a rough guide, one ton equals 14 cubic meters (the volume of one ton of liquid hydrogen).

Originally Posted by p. 21

Deck Plans: If the referee or the designer should feel that detailed deck plans for a ship are required, then they may be drawn up using square grid graph paper. The preferred scale for the interior should be 1.5 meters per square, with the space between decks put at about 3.0 meters. One ton of ship displacement equals approximately 14 cubic meters. Therefore one ton equals about two squares of deck space.

But:

Originally Posted by p. 48

When determining the contents of a cargo, the players and referee must be certain to correlate the established price of goods with the cost per ton. For example, the base price of a shotgun is Cr150, while a ton of firearms as trade goods has a base price of Cr30,000. A strict weight extension of the shotgun (3.75 kg per shotgun) would indicate 266 shotguns.

Similarly, the "tons" listed for ground and air vehicles in the starship design tables (p. 23) are identical to their masses in metric tons (Book 3, pp. 21-23).

There's no mention of 14 cubic meters or 1.5 meter squares in the first (1977) edition of Book 2. The latter first appears in Snapshot (1979), which was explicitly scaled for 15mm (1:107) figures (though the actual scale is 1:118). Note that a metric ton of liquid hydrogen is more like 14.3 cubic meters than 14. The deck plan advice quoted above results in 13.5 cubic meters per ton: within the recommended 20% leeway, but MegaTraveller (Ref's Manual, p. 57) actually made this (= 0.945 metric tons of liquid hydrogen) the standard.

So, here's the heretical thought: forget the 14 cubic meter displacement ton, and define the "mass displacement" ton from Book 2 as one metric ton, displacing one register ton (100 cubic feet, or 2.83 cubic meters) of volume.

This isn't as bizarre as it sounds. The starship design system is mostly arbitrary. Controls, drives, and fuel are percentage-based for the most part, so the proportions remain the same even if the absolute size changes. The major impact is to quarters: a 4-ton stateroom goes from 56 to 11.3 cubic meters. This is cramped but not impossible: NASA studies concluded that 7-12 cubic meters per person is adequate long term. Even double occupancy staterooms and small craft cabins (5.66 cubic meters per person) exceed the NASA baseline 4.25 cubic meters per person for up to 60-day durations.

Existing classic Traveller starship designs could be used with their listed statistics (100 metric or register tons for a Type S) or by multiplying the listed tonnages by 5 (a 500-ton Type S). If the former option is selected, the deck plans are still usable as-is by interpreting each 1/2" square as 0.75 m and using 25-28mm (1:64 or 1:58) figures. At this scale, two 0.75 m x 0.75 m squares with 2.5 m from deck to deck (2.0 m clear + 0.5 m interdeck) would make one ton. Again, a 0.75 m x 2.0 m (2.5' x 6.5') corridor is cramped but not impossible.

The advantages of this approach are twofold:

First, it allows one to mingle or swap Traveller starship designs with other, primarily mass-based systems (such as GURPS Spaceships) and with real-world cargo statistics.

Second, it corrects the weird perception that Traveller starships are smaller than they actually are. A 200-dton Free Trader has the cargo capacity of a C-5 Galaxy. A Saturn V was 2,970 metric tons, but only 440 dtons. Kinunir is the size of an Ohio-class ballistic missile submarine.

[thrash]

Marc Miller commented on a related thread in the Facebook Classic Traveller group:

This ‘mass’ [in the Book 2 drives table] was written early in the design process. It evolved into the volume tons as the game prigressed [sic].

[Rupert]

Originally Posted by thrash

Second, it corrects the weird perception that Traveller starships are smaller than they actually are. A 200-dton Free Trader has the cargo capacity of a C-5 Galaxy. A Saturn V was 2,970 metric tons, but only 440 dtons. Kinunir is the size of an Ohio-class ballistic missile submarine.

On the other hand, if Traveller spaceships are using tons/tonnes mass and register tons volume, the largest Book 2 spaceship (5000 'tons') is under half the size of a WWII Liberty cargo ship or a cruiser.

Multiplied by five, a Liberty ship equivalent is 2-3000 tons, and a 5000 ton ship is a pre-WWI dreadnought in mass.

However, the tone you want in your game is probably the important thing - your base suggestion makes for small, cramped vessels, with aeroplane or submarine-like living spaces and access-ways. It also means bulk cargoes are probably not viable, so shipping will be like air freight 30+ years ago.

If you want fairly spacious ships, perhaps to emphasise that it's the far future and space travel is clean, comfortable (at least if your ship is new), and a mature technology you'll want the larger ships.

[ak_aramis]

Originally Posted by Rupert

On the other hand, if Traveller spaceships are using tons/tonnes mass and register tons volume, the largest Book 2 spaceship (5000 'tons') is under half the size of a WWII Liberty cargo ship or a cruiser.

Note that register tons are not ship's volume, but ship's enclosed cargo volume (in units of 100 ft³, or roughly 2.83 m³).
(see http://www.ibiblio.org/units/dictT.html entry: ton (RT or rT) [3])

So, if using them as the volume baseline, the TTB Type A is 82 Registry Ton, not the hull's 200 Td.

Let's see what the actual mass-volume ratio is for a couple wet drives, and use that as an extrapolation for drive volumes...
KTA-650 Marine LOA 2.694m, WOA 1.564m, HOA 2.260m, mass 5.166 Tonnes. BB Vol ≅ 9.52 m³. 1.84 m³/T
QSK60 Marine LOA 3.290 WOA 1.757 HOA 2.415, M 8.754. V≅13.960 m³. 1.595 m³/Tonne
QSK-95 Marine L 3.654 W 1.733 H 2.362 M 12.916 V≅ 14.957m³. 1.158 m³/Tonn
about 1.53 m³ per tonne. So, doubling that (to allow work space, as none of these include work space) gets us right close to 3m³. Let's call that 1.1 Tr.
We'll take as given the 14.3 given above for tons of fuel extracted from water and GG's... so that's 5 Tr per Ton of fuel.

So, taking the TTB Type A, we get
82 Tons, 82 Tr Cargo.
15 tons, 16.5 Tr Drives & workspace
30 tons, 150 Tr fuel
73 tons, 73 Tr Everything else

we wind up with 321.5 Tr of volume, or roughly 1.5 Tr per Ton..
If, however, the fuel isn't LH₂...
D₂ not H₂ (which is double the density) that's 6.15m³/tonne
CH₄ (Methane) or NH₃ (Ammonia), we can get ≈0.7 tonnes per m³ or 1.4m³/Tonne. So... 0.5 Tr per Tonne.

Everything there releases energy in fusion... theoretically and/or in stars...

So... if the ton is linked to registry tons, a non-protium fuel makes for easy play. (on the other hand, it makes the question of how long frontier refuelling from water takes much more interesting, and explains the benefit of unrefined fuel from the pump... 1.76 to 3.4 µMol/m³ of CH₄, and, if I understand the unit conversions 0.5 to about 4 µMol/m³ of NH₃.)