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The Fleet Ship designs, strategies, and tactics.

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  #1  
Old March 2nd, 2003, 12:29 PM
Tom Schoene Tom Schoene is offline
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I don't know if I've pointed this out before or not, but the thread on J-6 couriers reminded me of it.

The T20 rules for drop tanks (THB p. 267) are pretty much identical with those from High Guard. But T20's rules on fuel usage in jump (p. 354) should change things. T20 says a ship uses only ~80% of its jump fuel to initiate the jump and burns most of the remaining ~20% during jump to sustain the field.

This means that if you plan to discard drop tanks at the beginnning of the jump, you need to have 20% of the fuel requirement for that jump in your internal tanks, not the drop tanks. Othwerwise you're leaving behind fuel that you'll need during the jump. (This is hinted at in the last paragraph of the drop tank rules, but never said explicitly.)
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Old March 2nd, 2003, 01:49 PM
far-trader far-trader is offline
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Heh, beat me to it Tom Schoene [img]smile.gif[/img] I had been thinking of starting a drop tank thread for those not already aware of all the issues beaten to death around it. And I was going to begin with the T20 80/20 rule. So on to my next issue with drop tanks...

Using T20 as an example, since the thread is so named and begun (though other systems will no doubt come into play), my problem is not with using the tanks as described for a fast burn and drop prior to jump but actually jumping with them attached or manuvering with them. The tanks are listed as costing a mere Kcr 10 plus Kcr 1 per dT of fuel capacity. Given the cost of a simple ship hull is Kcr 50 per dT and up I find it hard to believe a drop tank could have the structural integrity needed for manuvering or the jump grid needed for jumpspace. Also there is no mention of if you need more bridge allotment to cover the drop tank tonnage or not. Some of the other systems made you penalize streamling when the drop tanks were carried but this is also not addressed in T20 unless I missed it.

My suggestion, keep the p. 267 text as is with the inclusion of the 80/20 fuel usage rule here too but drop the last two sentences and the description line at the end and replace it with something like:

L-Hyd Drop Tanks: Tanks must be built and purchased as an empty hull. They are treated as a carried craft in an external docking mount (p. 274). This specialized docking mount cannot be used for normal craft but is dedicated to drop tank usage and rapid fuel transfer only. The 30% extra volume in the docking mount includes volume for the extra 20% of the fuel that must be retained through jump.

Alternatively a standard docking mount may be used for a drop tank if allowance aboard is made for the 20% fuel required. This is in addition to the normal 30% required for umbilicals (5%), launch and recovery grapples (5%) and airlock access (20%). If access to the craft/drop tank is not required dismountable tanks may be installed in the normal airlock access volume for the 20% fuel margin. In some cases specialized small craft are built to use such an arrangement, giving the ship the option of a dedicated small craft for rapid refuelling when retained or a drop tank that can then independantly skim more fuel and be ready for the next ship that arrives.

For example: An architect desires a drop tank with 100 dT of jump fuel for a ship. The external docking mount will require 30 dT inside the mother ship, but will include 20 dT to retain the fuel margin to see the ship through jump when the tanks are dropped. This 20 dT of fuel capacity may also be used for other purposes if filled and not used for jump. The base cost of the mount is Kcr 120 but to avoid the streamlining penalty we'll pay Kcr 240. The tank itself will be a sphere to allow gg fuel skimming (partially streamlined). While carried by the mother ship (fully streamlined) the ship is reduced to the drop tank's partially streamlined factor. If we had chosen a streamlined tank, at more expense, the mother ship would retain its fully streamlined aspect even with the tank attached. The tank will cost Mcr 7.0 before discounts.

Historically drop tanks do not come into use until about the year 1100 in the OTU but they may be built at any TL supporting ship construction. The major reason they are not widely used is safety. No commercial vessel carrying passengers is allowed to use drop tanks and most commercial operations do not use them even for freighters because of the added expense for hazard pay scale for the crews and higher insurance for possible loss.

Firms may be hired at most starports to recover drop tanks and store them for use upon return. Costs are as per p. 350 for cargo shuttle service (x10 for 100d to orbit) and orbital berthing, paid in advance. Tanks dropped without arrangement for such service are considered abandoned and fair salvage. Tanks left in orbit beyond the prepaid berthing fee are held by the recovery service for 30 days before becoming the property of the recovery service. If reclaimed before the 30 days the penalty is double the 30 day storage fee, regardless of the actual lateness of the claim.

The militatry maintains their own recovery service, and all military drop tanks are considered contracted even if apparently abandoned. The military does pay reasonable finder fees and salvage costs for temporarily uncollected drop tanks that are returned to them.

Some large corporations are experimenting with drop tanks and also have their own recovery service. These will often take private recovery and storage contracts as well.

Note:

This is still undergoing some editing and its rather simplistic. For example the example above could provide 120 dT of fuel, but as only 20 dT is onboard if the tanks are dropped it still limits the jump to 100 dT total in dropped mode. The 120 dT could be used for retained mode jumps though, or you could fiddle the requirements so the drop tanks are just enough for the 80% and expand the onboard enough to keep the 20%. I'll look at that for the next edit.

Hmm, simplest might be to say the 20% "lost" in the drop tank is due to the rapid transfer requiring a 20% expansion volume aboard the ship. i.e. the drop tank pushes the full 100% a little faster than the j-reactor can burn it. This results in the 20% aboard backfilling until you reach the point of 80% burned, 20% backfilled, and the tank is empty.

Also note the % breakdown for the docking mount is just my own little invention from the rules simple 30% total, so you won't find it in the book.

Critique, cudos, questions?
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  #3  
Old March 3rd, 2003, 05:40 AM
Liam Devlin Liam Devlin is offline
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Hey guys, here's a TNE solution to your "drop tanks".
"Icing:The use of solidified Hydrogen, stored in external mountings, as jump and reaction mass. Fuel is the largest consumer of space aboard a ship, with even a j-1 ship giving about 50% of its displacement to fuel tankage. With each one parsec increase in jump range, comes a corresponding 6% drop in capacity, to the point that jump 4 through 6 ships are unprofitable for large scale trade. Since most of the ships fuel mass is going to be consumed by the process of jumping, it will arrive at its destination with huge, empty, and unprofitable fuel tank.

But in the 1150s, the engineers for a new Regency freight line called Mamano Lift, resurrected an old idea first proposed by a Solomani scientist long before jump drive: an ice rocket. An ice rocket doesn't have a fuel tank, rather its frozen fuel IS the fuel tank, which is consumed with the fuel itself. Unlike the methods needed to obtain MMH (Metastable Metallic Hydrogen) freezing hydrogen is easier and cheaper, and only requires a suitable freezing medium in order to become profitable. Earlier attempts at lower tech levels relied on lasers for cooling the fuel mass; but Mamano Lift relied upon a derivative of military Black Globe technology to freeze huge masses of fuel. To this company engineers added a damper field to compact the fuel mass, further enhancing performance.

An "Icy" is generally a needle, open frame, cylinder or sphere configuration hull. Around the axis of the hull are large circular aprons, to which the fuel mass is affixed. Finally, simple toroidal shields made of metal protect the fuel mass against ablation by magnetic fields or solar wind. When the vessel jumps, the entire fuel mass is instantly converted to creating a jump field whose dimensions are based upon displacement MINUS the now consumed fuel mass, giving unheard of jump performance for large cargo vessels.

Besides revolutionizing freight haulage at a time when the Regency needed it, the military applications of this technology were also decisive. Icing military ships before they manuever and jump away for hostile territory permits them to preserve their internal fuel tankage unused, meaning that an attacking task force no longer has to refuel when arriving insystem, and can avoid the defense forces that lie in ambush in gas giants or water bodies. It also permits longer ranged patrols into rift areas."
-Peter Gray/ Science in the regency
http://www.panpub.com/traveller/rule...ncy_tech2.html

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Also brings us back to certain posters versions of "gas station set ups" for systems "wildcatters".

The gist of the above condensed: Make the (frozen) Lhyd fuel externally mounted as well as internally- consume it in the jump acceleration/ arrive with full tanks wherever yer going! Militarily one can see the advantages! commercially-hey- you can get to places you couldn't before!!!
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Old March 3rd, 2003, 07:07 AM
Tom Schoene Tom Schoene is offline
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Solid hydrogen is pretty hard to keep that way. It needs to be cooled down around 7 Kelvins, and it probably won't stay frozen without some serious effort, even in space. (Get in sunlight and it's going to sublimate rapidly, I suspect.)

If you're looking to reduce the volume required for jump fuel, there are lots of other easier solutions. Ammonia is a nice option that; on a volume-for-volume basis it holds significantly more hydrogen than Lhyd. Even water would be more compact than LHyd for a given amount of H2.

[Edit: subsitutuded ammonia for methane. Got my hydrogen-bearing compunds confused.]
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Old March 3rd, 2003, 01:59 PM
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IMTU-IMHO-IIRC
Acronyms aside, I would say that the ice needles (whether frozen ammonia, Freezing point is at 195 K; or frozen Lhyd, freezing point at 7 K) sort of change the whole feel of Traveller. To wit, Travel requires larger and larger amounts of fuel, ships need lots of internal space dedicated to be able to go far, and the 80/20 rule allows some fudging and variation in design that was missing from the LBB/Book 2 design sequences. But Personally, I am going to stick with the 80/20 and most of the fuel being internal, drop tanks being a special bonus that the characters can try to work towards, like the upgraded sensors and turrets they want in their ship. I guess I enjoy the Gearhead stuff, so long as it compliments fun game play.
YMMV
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Old March 3rd, 2003, 03:40 PM
Tom Schoene Tom Schoene is offline
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Fletch, sorry, I wasn't clear. I didn't mean frozen ammonia. Liquid ammonia in internal tanks has about 1.7 times as much hydrogen by volume as LHyd.

A ship built this way could save maybe 40% of the volume needed for fuel. The fuel will weigh more, of course (about 7 times as much, even counting the reduced volume) but there are a few applications where it might be worth the trade. (and of course, CT and T20 don't care about mass, just volume.)
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Old March 4th, 2003, 05:40 AM
Liam Devlin Liam Devlin is offline
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Metastable Metallic Hydrogen
"When ordinary mono or diatomic hydrogen is compressed at pressures in excess of fifteen to twenty thousand atmospheres, internal repulsion between hydrogen atoms is overcome and metallic bonds are formed. This condition is "metastable", meaning that this substance only exists within a narrow range of circumstances, and will quickly revert to a more normal equilibrium with the right stimulus, such as compression in a fusion reactor. Nevertheless MMH is a very lightweight material, comparable in strength (though not density) to aluminum, and can be used as a strutural material in some commercial applications.

MMH naturally occurs in stars and gas giants where the weight of the atmosphere and density of the gas become sufficient for its formation. At a depth of around 1000 to 2000 kms, a metallic "surface" of hydrogen will form in these bodies, one capable of conducting heat and electricity in the same manner as all other metallic substances. The existence of this phenomenon (Authors note: The following is merely my own educated opinion.) is important to the reconciliation of fusion processes, both "hot" and "cold" at TL-9. Cold Fusion is in a solid state, where a metallic catalyst creates a "crystal" of hydrogen that fuses into helium. Further surveys of solar "hot" fusion, where a high pressure solution of metallic hydrogen is mixed with metallic catalysts, is virtually no different than cold fusion, except for the scale. All working fusion reactors that have ever existed are high pressure gas-metal catalytic cells which compress powerplant hydrogen to a metallic state, thereby creating a fusion process that can be utilized for useful power. "
-Pete Gray

http://www.panpub.com/traveller/rule...ncy_tech2.html
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Now I admit this is more gearheaded than something i could concoct. But, IMHO, not too big a heresy. Then again, I am a TNE heretic [img]graemlins/file_22.gif[/img]

Tom: As for sunlight, this varies in degrees of warmth in space, the further you go out from a primary. A refuelling station set up orbitting a gas giant in the outer zone might not have that to deal with.

Father Fletch: Sorry if this idea loses Traveller flavor. YMMV, IYTU, do as thou wilt!
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Old March 24th, 2006, 09:19 AM
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As far as using ammonia goes, would you need to modify the ships fuel processors to deal with ammonia? Water and gasses sucked off a planet are one thing but does ammonia split as easily as water, say in an electric current?
Otherwise a free 40% reduction in fuel mass (T20)is way too generous to give to players.

Also a question-- in T20 it states under drop tanks that by ejecting the tanks you may increase jump range by lowering vessle mass. How? It is mentioned in two places in the book I can find but both are vague one line statements and make no sense as far as game mechanics go.
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Old March 24th, 2006, 11:09 AM
Andrew Boulton Andrew Boulton is offline
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With drop tanks fitted, a ship might be, say, 400dt and manage J4. If it uses the fuel and drops the tanks, it might drop to 300dt and reach J5.

Hey, I've just had an idea: rather than drop tanks, use external collapsing tanks! You get the extra range, but you also get to keep the tanks!
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Old March 24th, 2006, 11:28 AM
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Ok thats a little more info, but the HOW still escapes me. If you install J4 drives you can jump 4 parsecs. Doesn't have any modifiers I can find as to ship mass.

According to THB you don't actually HAVE to drop them, but that means no performance improvements I think.

:&gt;
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