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 Densified Fuel Storage

The Problem

A major source of complaints in ship designs for Traveller, when using any of the standard rule sets, is the necessity for allocating major portions of hull space for fuel storage. At the same time, the reduced cargo capacity and increased cost of fuel makes most starships economically marginal at best, and impossible at worst. Given the description of purchasing a ship in the standard rules, it could be considered strange that most far and free traders aren't 'skips' (evading repossession for nonpayment).

Jeff Zeitlin proposed one method of alleviating the above problem (the Lyman Jump drive), and I will propose another in this article.

The Proposal

Densifying fuel storage (sounds a bit dumb, but that's what NASA et al call it) means what it sounds - increasing the density of the hydrogen fuel that Traveller ships guzzle by the shipload.

This has one of two results:

  1. For the same mass of fuel stored, less volume (and thus less fuel tankage) is required.
  2. For the same volume of fuel stored, more fuel can be carried.

So what does this mean in my Traveller universe?

Simple. Ships either become more profitable, less loss-making, longer-ranged, or some mix thereof.

Fuel Density Increase With TTL
TTL Density Multiplier
10 (A) 1.05
11 (B) 1.08
12 (C) 1.11
13 (D) 1.14
14 (E) 1.17
15 (F) 1.20

(see Propulsion Systems from Takeoff to High Speed Flight, American Institute of Aeronautics and Astronautics, 1990, for the maximum density increase.)

This goes one of two ways:

Same mass, less volume:
  • Divide tank volume by density multiplier, rounding odd spaces up, and record the number of spaces freed up.
  • Multiply original, undivided tank cost by density multiplier.
  • Empty tank mass remains unchanged (extra insulation and cooling systems, plus a preheat system or routing fuel feed through a source of heat, to reliquify the fuel before feeding into the drive reactor, account for this.)
Same volume, more mass:
  • Tank volume remains unchanged.
  • Multiply original, undivided tank cost by the square of the density multiplier.
  • Multiply empty tank mass by density multiplier.

Note: To make densified tankage work without requiring any modification of external fuelling infrastructure, thus preserving the vessel's freedom of movement, a modified refining unit (capable of both refining and densifying fuel, which Jeff Zeitlin has christened a slurryfiner), needs to be installed, giving the ship both active and passive methods of keeping the fuel in a slushy state. A slurryfiner can either densify and refine fuel at half rate a fuel processor of its TL would normally refine fuel, while doing the same, or can concentrate on densifying fuel at double the densify-and-refine rate.

In GURPS Traveller, fuel refiners refine raw fuel at 8 dton/hour, so a slurryfiner would refine and densify raw fuel at 4 dton/hour, or densify refined fuel at 8 dton/hour.

If, for some reason, tanks and slurryfiner of mismatched TL are installed, use only the lowest TL to find the fuel density increase.


The 200 ton Ladyhawke-class Far Trader, Dusk Till Dawn, is getting its fuel tanks done and the owner has decided to shoot for more cargo space. Per GURPS Traveller Shipyard, the 40 tons of tankage (GT ruleset, GTL8 Cryonic Internal Tank) costs MCr6.8, takes up 40 dton, and masses 13.2 ston empty.

Since only GTL10 (TTLC) kit is available, the owner, being a rather pragmatic businesscritter, rolls with it, giving us a density multiplier of 1.11.
Tank volume - 40 / 1.11 = 36.03... = 36.5 dton, freeing up 3.5 dton
Empty tank mass remains unchanged.
Tank cost becomes MCr6.8 * 1.11 = MCr7.548

The owner also installs a modified half-dton slurryfiner, claiming 0.5 dton of the space freed up. This started life (in the GTS repository) as a Small Fuel Processor, 0.55 ston, MCr0.425.
Volume remains unchanged = 0.5 dton
Cost becomes MCr0.425 * 1.1 * 1.1 = MCr0.515
Mass becomes 0.55 * 1.1 = 0.605 ston


Prima facie, dense tanks would appear to automatically improve the viability of whatever ship they are installed/retrofitted in, with the improvement increasing with tank TL.

Unexamined assumptions have tripped up people great and small throughout history, so we'll take a look-see, noting that for maximum independence of movement and compatibility with existing fueling equipment, a slurryfiner is either installed alongside existing fuel refining kit, or retrofitted. If retrofitted, only the difference in cost is paid.

For an example, I will use the Empress Marava-class Far Trader from GURPS Traveller p 135, and note that GTL 10 roughly equals TTL12. I will use the method used by Robert Prior in 101 Starships, breaking out only the costs of operating the vessel, and comparing them to the baseline version, assuming J-2 tramp service, full hold, 25 jumps per year, 80% loan financed over 40 years at 5.56% pa (GT:FT p98, "Bank Financing").

As per the writeup, the boat has 6 crew - skipper/pilot (Merchant Rank 5), navigator (Merchant Rank 4), sensor/comm operator (MR 3), steward (MR2), two engineers (MR1 and MR0, paid as an officer and crewman), occupying 4 staterooms (skipper and navigator single-bunk). Relevant skill levels are assumed to be 12, leading directly to:

Skipper: Cr1200 + Cr1000 = Cr2200/mo
Navigator: Cr1200 + Cr800 = Cr2000/mo
Sensor/comm: Cr1200 + Cr600 = Cr1800/mo
Steward: Cr1200 + Cr400 = Cr1600/mo
Engineer: Cr1200 + Cr200 = Cr1400/mo
Deckhand: Cr960 + Cr0 = Cr960/mo

Total payroll: Cr9960/mo, Cr115,920/yr.

In addition to payroll, the two other major fixed costs are the loan payment, and annual maintenance (as per GT rules, 0.1% of purchase price per annum), which will naturally vary with the ship's sticker price.

The variable costs are those incurred per-jump, namely fuel and port fees (GT:FT p66).
Fuel - Cr350/dton (assuming fuelling at berthside), 40 dton/jump, Cr14,000/jump
Berthing costs:
Berthing fee - Cr20/dton, 200 dton ship, Cr4000/jump
Starport fee - Cr500 flat fee, Cr500/jump
Pilot fee - Cr100 flat fee, Cr100/jump
Base variable costs per jump: Cr20,600/jump

Handling fee is not listed as that will naturally vary with the amount of cargo being handled.

Comparison of costs
Empress Marava-class Far Trader
  Base Case* TTL A
New Build
New Build
New Build
New Build
TTL D Refit
Fixed Costs
"Sticker" Price (MCr) 42.280 43.067 42.658 43.283 42.884 43.500 43.111 43.785 43.456
Cargo Hold (dtons) 49 50.5 51 51 51.5 52 52.5 53 53.5
Maintenance (Cr/yr) 42,280 43,067 42,658 43,283 42,884 43,500 43,111 43,785 43,456
Loan Payment (Cr/mo) 175,838 179,108 177,407 180,009 178,349 180,910 179,290 182,094 180,728
Loan Payment (Cr/yr) 2,110,046 2,149,285 2,128,880 2,160,102 2,140,177 2,170,919 2,151,476 2,185,121 2,168,726
Total Fixed Costs (Cr/yr)** 2,268,246 2,308,309 2,287,458 2,319,305 2,298,981 2,330,339 2,310,507 2,344,826 2,328,102
Variable Costs
Cargo Handling Fee (Cr/jump @ 20 Cr/dton) 980 1,000 1,010 1,020 1,030 1,040 1,050 1,060 1,070
Total Variable Cost (Cr/jump) 21,580 21,600 21,610 21,620 21,630 21,640 21,650 21,660 21,670
Total Variable Cost (Cr/yr)*** 535,900 540,000 540,250 540,500 540,750 541,000 541,250 541,500 541,750
Total Operational Cost (Cr/yr) 2,807,746 2,848,309 2,262,708 2,859,805 2,839,731 2,871,339 2,851,757 2,886,326 2,869,852
Capacity (dton-pc/jump) 98 100 101 102 103 104 105 106 107
Capacity (dton-pc/yr) 2,450 2,500 2,525 2,550 2,575 2,600 2,625 2,650 2,675
Operational Cost (Cr/dton-pc) 1,147 1,140 1,120 1,122 1,103 1,105 1,087 1,090 1,073
Additional Costs For Densified Fuel Storage
New Fuel Tank Volume (dtons) 38.5 38.5 37.5 37.5 36.5 36.5 35.5 35.5
Displacement of Slurryfiner (dtons)**** 0.5   0.5   0.5   0.5  
Net Cargo Increase (dtons) 1.0 1.5 2 2.5 3 3.5 4 4.5
Cost of Slurryfiner (Cr)**** 446,250 37,350 459,000 59,760 471,750 82,170 552,330 223,802
Fuel Tankage Cost Increase (Cr) 340,000 340,000 544,000 544,000 748,000 748,000 952,000 952,000

* Base Case uses standard fuel system. All other cases use indicated TL densified fuel storage system; "New Build" indicates densified fuel storage planned at time of laying keel; "Refit" indicates conversion of standard fuel system to densified system after ship in service.
** Total Fixed costs include annual loan payment and annual maintenance costs from table, plus Cr115,920/yr payroll, per crew requirements above.
*** 25 Jumps per year
**** In Refits, the displacement of the slurryfiner need not be considered, as it replaces an already-extant standard refiner.  The cost given in those cases is the incremental cost.