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Merchant Drop Tanks


Just wondering if anyone else out there had considered drop tanks for civilian shipping.

For background, consider that you have a subsector where all of the high-population worlds are 3-4 parsecs apart. Large merchant shipping companies (the ones using multi-Kiloton stansports, not to be confuesd with the "tramp traders" used by most PC groups) are unlikely to find anything of interest to trade in the intervening area, so they build jump-3 and Jump-4 ships to service their "core" market.

As soon as you have ships of this size (especially on regular scheduled transport routes) it makes a lot of economic sense to cram them to the gills with cargo, and that 30-40% hit off the top to carry jump fuel has to be a nasty one, especially if a merchant combine is jumping a ship a day back and forth.

At this point, some bright fellow will notice that the cost of using drop tanks, and having a tug in each system to tow the "empties" back to base for reuse is a lot cheaper than leaving 30% of the hull of the merchant ship "empty" (not generating revenue). With this in mind, I'm working on the specs for a 10 Kton merchant ship with Jump-4 but less than 20% fuel tankage (remember that I'm using TNE with no reactionless drives, so cutting fuel below 10% maneuvering reserve is asking for trouble) Also in the works for "keeping costs down" are banks of batteries to power the Jump Drive: why pay the premuim for a nuclear plant and carry the overhead of all those engineers for a power supply that is only used twice a month?

A variant on this is a design that has *only* FTL drives (OK, so it has .001G for maneuver) and is intended solely for interstellar transport of goods (a la toybots, er I mean battletech) with insystem tugs and tenders to resupply and shuttle cargo. (and yes, I'm doing a cheap commercial X-Boat redesign for FF&S as well...)

Any comments on why this is a bad idea? (Other than the obvious: I already have an adventure planned for a sabotage and deliberate misjump, but most companies have security forces for just this reason...) Take into account that this is specifically for regular transport runs between two well established (and well patrolled) high population worlds nowhere near a war zone. Actually, without a war in the sector in over a century.

Scott Martin
Using the Traveller rules to put drop tanks on jump ships makes excellent economic sense.

Problem is that in the OTU setting the use of drop tanks is limited to high TLs (TL12+, High Guard first edition plus early TNS fluff). Some handwave about fast discharge/long duration jump capacitors or some such ;)

And, as an early TNS bulletin also points out, isnt't without some risk - although it could have been terrorists

This TL restriction isn't mentioned anywhere else though...

I think it's a good idea.
Oh sure, Sigg gets here first so I get to be the bad guy and point out some flaws ;)

Minor flaw as mentioned is the TL and need for the high capacity accumulator. The accumulator is only in HG1 though (TL12 MCr0.5). That rule and a couple others seem to have been forgotton or dropped in HG2 which doesn't require any TL or extra cost for drop tanks. T20 btw says the TL for drop tanks is 15.

A little bigger problem is the ruling (MT iirc and T20) that the use of drop tanks (if dropped during jump) imposes a higer risk of misjump. This means, to me at least, that no commercial shipping would use it, or be allowed to use it. There's no way they'd get certification or insurance. T20 seems confused on the issue. It says "Because of the risk, this method is never used by commercial ships. In the OTU, drop tanks are not available for commercial ships until the 1100s." So which is it? Never used or unavailable until the 1100's? I vote for never used and the second sentence should drop the word "commercial".

Now then there's also the issue of the actual fuel used. The implication of the drop tank rule is that you can drop 100% of your needed fuel. This feels wrong. And according to MT (iirc) and T20, as well as implied in the (only?) OTU CT example (the Gazelle) it is wrong. In general you need to keep about 20% of the required fuel for any jump in internal tankage. So your drop tank can at best save you 80% of your needed fuel.

I'd also say, if you want to set this in the OTU it won't work. If it could be done it would have been done. The reasons above don't seem like quite enough so there must be others. However for YTU go for it. You have said it's only in use in a very safe region and only on a limited run. Perhaps part of the problems above and others are negated because of the circumstances. Maybe your polity is not so rigid. Or the mercantile concern has worked out the bugs (mostly, or on paper) and has license to operate with them.

One other thing to consider if you use the bottom line as your reasoning is the cost of the tugs to collect the dropped tanks and ferry them about. It'll probably still be cheaper but don't forget them is all I'm saying. Part of this bottom line in MTU is the cost of the apparatus. The Cr10,000 part of the drop tanks (Cr1,000 per ton plus Cr10,000) is a single use expense in MTU. So it will cost that to fit and use them, each time. I also don't see the tanks being serviceable indefinitely at that cheap price. In MTU they have to be replaced annually (at maintenance) or be prone to leaking and failure. Each drop usage adds one month to the normal usage in terms of wear, neccesitating more frequent replacement. More durable tanks would probably cost Cr10,000 per ton or more.

I would (and have considered it myself) as you mentioned make the starships non-maneuver and have the tugs pull extra duty as not just drop tank herders but cargo shifters between the starships and starport (high and/or down) as well, and if needed in groups as tugs for the starships themselves to bring them into port and tow them out to 100d again.

All in all I have to agree it is doable if you want it :D
The "non-maneuvering" jumpship was inspired by the original Xboat (which you can easily do in a TNE 100T vessel).

Since Jump-3 requires Tech 12 anyway (note below) the "High tech" requirement is already there. I read that they were considering only alowing drop tanks to be used by T15 ships, but this would go against Traveller "Canon" since the original Gazelle (the first ship to have drop tanks, in LBB Supp 7 I believe) was TL 14. Since HG came out in 1979, and T&G came out in 1980, this was probably a lot of peoples first looks at both PAW's and barbettes in Traveller.

Scott Martin

High Guard and subsequent books have J1 at tech9, J2 at tech 11 and 1 increase per tech level above that. LBB-2 allowed you to build small jump-6 vessels at low tech and can be "integrated" by putting a jump cap on LBB2 designs.

In case anyone cares ;)
Had a couple more thoughts to add to the post above you might have missed while replying, fyi

I also agree on the TL15 being contrary to earlier examples and ignore it.
Hi Far-trader

Don't you just hate it when someone posts at the same time you are ;)

for my traveller universe I have a *lot* of FTL restrictions to limit the use of "Killer Rocks" (C-Fractional missile strikes) and may post my house rules for them at a later date (once they're cleaned up)

The rules / library data entries for "Drop Tanks" always confused / annoyed me, and gave me the idea that they had been introduced as a cool idea, but the reprucussions hadn't been though through, so later "History" was adedd to restrict them.

The first "Canon" appearance of a ship with drop tanks was in Supplement 7 (Traders and Gunboats, in 1980) and there was *no* mention at all that there was an increased risk of misjump, or that the Gazelle needed to keep any internal tankage for the jump. As for High Guard first Ed. I have never seen it, so it hasn't shaped my view of the OTU. I certainly wouldn't deploy a system on a military vessel that increased the risk of dispersing my forces, so if this was an issue I'd expect to see the military using tankers instead of drop tanks, with the scout service using Drop Tanks (Guess we'll just have to survey these systems on the way back home...)

Tangent Warning

I'll give you my impression of a "typical" high tech high population system nowhere near a combat zone (AKA most of the Imperium in 1100) which further push the idea of FTL only transports as making a lot of economic sense (since the infrastructure is already there!)

-There is likely to be a (very) high port in high-population systems, which would be anchored a few thousand (or tens of thousands) of km from an easily plottable jump emergence point. Systems at the nexus of many trade routes may have one per "entry vector" (depends on how FTL works in your universe)

-The presence of the VH port makes Search and rescue a LOT easier in case a vessel suffers an engineering casualty (AKA something important breaks) since help is minutes away after jump emergence instead of hours away.

-There will be several refineries orbiting local gas giants with fuel skimmers making scheduled passes into the gas giants atmosphere and dropping off the unrefined fuel to the refinery.

-The refineries will also stock "rare" gasses (Argon etc. for use as Ion propulsants, more "exotic" gasses / liquids as trade items) since they need to extract these anyway to purify the fuel

-There will be a fairly constant rotation of Fuel tugs ferrying (refined) fuel to the VH Port and empty tanks (and possibly goods / spare parts) to the refineries. Note that this means that refined and unrefined fuel will be almost exactly the same price, since most of the cost is due to shipping.

-There will also be a scheduled rotation of transports from the "VH Port" to the High Port orbiting the more populous bodies of the system

-Depending on the level of deep space activity (Mining etc) there may also be traffic between nodal (metal) refineries and the VH port: while LH is "cheap" that doesn't make it free, and warehousing durable goods at the top of a gravity well makes a lot more sense than storing it at the bottom af a well. (Of course in the case of a catastrophe (say, a computer virus that destroys your civilization) having huge "system" stockpiles where you can't reach them to rebuild your civilization could be quite frustrating...)

This introduces some interesting juristictional issues: do you have "Customs" at the VH port, or at "ports of entry" farther insystem? IMTU "Imperial" law applies at any deep space location (including the VH port) which allows the trans-shipment of commodities that may be considered "contraband" in the local system for transport to further systems. An example would be a shipment of hunting rifles to a frontier world from a high law level commercial hub. This shipment is illegal in by the law level of the local planet (system?) but since it isn't being unloaded there the "local" authorities shouldn't need to search the cargo. This also keeps the vast majority of "free traders" or "tramp traders" away from your high population planets, and allows the locally dominant merchant cartels to keep their "insider advantage" for goods in this system.

From a political / milatary standpoint, most systems will use the VH port as a quarantine facility and emergency quick response staging area. "Repressive" governments would use the Vh port to keep "Intellectual contamination" from happening (which would make this kind of government more, rather than less likley to survive the Virus)

Anyway, enough rambling, I should finish my requisite yard work while there is still light!

Scott Martin
The idea of drop tanks was introduced in TAS bulletins in JTAS 2-6, which was round about the publishing of High Guard 1.
The Gazelle was originally presented in JTAS 4. A LBB2/HG hybrid using drop tanks and PAW turrets from HG, it also has a nuclear damper ;)

The increased risk during jump was a result of a Tukera liner blowing itself to pieces - although TAS reports hint that it could have been the result of sabotage.

I'd ditch the T20 TL15 restriction too ;)
First, Scott, welcome! :D

Second, the idea of drop-tanks will only have one other problem, and that is "How jump works". If it works the "right" way for you to have drop-tanks in YTU, then no problem. (Unless, of course, you have a gearhead who disputes - usually with equations - how jump works.

One improvement might be to actually make the tugs streamlined (minimally) for scooping, with onboard refineries, and facilities for filling the drop tanks. That way, they actually plug up to the drop tanks (probably internally), run to the nearest GG, scoop, refine, fill, run back to the jump point. Good business for some entrepeneur...

As far as a VHP, that is a sensible idea that has been batted around elsewhere on these boards (somewhere). It doesn't make a lot of sense for most of your high-volume stuff to be hauled up and down the g-well by jump-equipped ships. Of course, having a maneuverless merchant ship seems a little dangerous.... :eek:

The legality issues would be handled (many here would agree) by the 100d limit - everything outside that is the Imperium's job. Of course, if you have a system-wide government, they will want to measure things in such a way as to maximize their control. I actually think, though, you're going to encourage Free Traders to bypass the VHP - docking costs are going to be higher, etc., just like at a big airport.
I did warn folks that I run a "Hard" SF universe right?

The "Maneuverless" jumpships actually have ion propulsion to the tune of a few mm/second. Nothing in terms of being able to fight, and stay the hell away from anything with a gravity well, but plenty enough to handle docking and the inevitable minor translation miscalculation. If jump were "Perfect" then your (Very) High Port would be an enormous docking cavern and ships can just jump directly into their assigned berths!

I had thought of modular fuel-skimming (and refining) tugs. The reason that I ditched this idea (having the tugs streamlined to do their own fuel scooping) is that the strain of "gas giant refueling" is extreme (noted in a number of other threads) At the very least I would expect it to vastly increase the wear (and thus maintenance costs) on whatever vessels are doing it. If I were to design something for GG refuelling I'd go for something unmanned with a fair whack of armour and a minimum of surface fixtures (Sensors, transmitters etc) to get sheared off during the procedure.

For an "established" High tech system with Gravitic technology I'd actually park a base on the planet (floating on a methane sea, or on one of the boundary layers) heavily inertially damped and (again) heavily armoured. Refine the fuel there and have a ferry to an orbital station that had sufficient stockpiles of fuel so that ther isn't an issue if the station suspends flight ops for a month or so due to heavy storm activity, and (even better) several stations on various parts of the GG so that "local" storm activity is unlikely to completely shut down your fuel supply.

Note that to "Float a base" on Jupiter you need at least Tech 13, to offset 4 of the 5 Gs of accelleration due to the gravty well ;) Jupiter is a bit better, but Uranus and Neptune (despite their remote location) would probably be better for this, and their extremem cold would be useful for "gas" seperation (at those temperatures you can use phase changes for refining "simple" gasses quite effectively: Methane is a solid!)

Once again, you will note that the "cost" of the fuel is largely to cover the shipment costs and the capital infrastructure costs: the refinery (as most folks have noticed in HG / MT / FF&S) is dirt cheap: the main "cost" is losing a small amount of volume that could be used for something else. I know its "Canon" but in a highly settled system I'd expect "unrefined" fuel to be rare and cost *more* than unrefined fuel, especially since these systems are *not* going to let you mess with their biosphere by filling your tanks from the ocean. (who knows where that filthy scout ship has been?)

Several other issues really revolve around whether "insystem" shipping is cheaper, or more expensive than "interstellar" shipping.

-If "Interstellar" shipping is significantly more expensive, then any system that has a shipyard (B Starport) and a large population (probably more than "8" or "Hundreds of Millions") is likely to have extensive insystem development (Cheaper to mine an asteroid than ship in steel)

-If Interstellar shipping is significantly cheaper than insystem shipping, then systems will tend to only develop the "prime" real estate, and you will see worlds shipping in high-volume low-value commodities (like Steel, Grain etc) and you will only see extensive insystem development if there is no source for interstellar trade for some goods within a reasonable range (say 3 parsecs).

The second option (Cheap interstellar transport) looks a lot more like the original traveller!

This is one of the reasons that I prefer "no reactionless thrusters" since it means that insystem freight can "cost" (in terms of expended reaction mass) more than the same materials purchased from outside the system.

And that would be the start of yet another long tangent.

Looks like I should start a thread on system infrastructure instead...

Scott Martin
The gas mining rig is a good idea, sounds like the sort of place a group of PCs could find themselves investigating various shenanigans ;)

Not sure why you'd need such a high TL for your maneuver drive though - the 6G drive in HG is TL9.
If you are using the TNE tech paradigm then the limit is the internal grav compensation, yes?
You can always borrow the rule from FF&S2 that allows for grav compensation to be stacked.

Oh, and Jupiter only has a surface gravity of 2.64g anyway, Saturn is 1.13g, Uranus 0.89g, and Neptune 1.13g. ;)
Yup, using TNE, since it's a pretty damn good for building "Hard" SF gear.

I remember Jupiter having a 5G field: My bad, thanks for the actual surface gravity values.

Comments on ease of refining based on phase transition still applies (Colder planets are easier) although your physical plant would need to be quite heavily insulated to keep it from melting / offgassing a huge area around it ;)

I remember the original discussions on "Stacking" compensators, and recall it being nixed: if it's allowed agan, then you have a new possibility for your "Blockade Runner" (Different thread)

Scott MArtin
It's allowed in Central Supply Catalogue's vehicle design rules, and FF&S2.

Any ideas for other items in the system infrastructure?
Hi Sigg

Sorry I haven't responded, Real Life (tm) has been a bit hectic lately.

A lot of the "infrastructure" is really a result of a "functionalist" design philosophy. Most of my heavy cargo transports (Solomani inspired, AKA "what is this 14 m3 'ton' of which you speak) haul cargo pods with an end cross section of 6m x 10m (generally either 20 or 22 m long).

This means that you can design modules that match this size for cargo transport, orbital defence platforms or Tugs (trust me you can pack a LOT of delta-v into 1200 cubic meters)

The tugs are one thing that springs to mind: most vessels have several points at which a tug can lock on (structurally braced with access to the "towed" vessels tankage) so that the tugs with their very powerful engines can maneuver unwieldly (1 m/s max accell or less) interplanetary vessels into dock.

Another thing that I would expect would be the storage of "durable" (not damaged by freezing or low pressure) gargos either in orbit or otherwise away from the "wells" in the system, especially in systems where the population is dispersed within the system (multiple habitable planets, any system with a depot or a large naval yard with a relatively small planetary population) This gives you the flexibility to ship anywhere in the system without needing to pay the energy (read "fuel") penalty for re-orbiting it.

This does leave it vulnerable to "raids" or theft but most "durable" cargos tend to be in the large volume / low value category so even this is arguable.

One of the nice things about the 3I setting is that you can think about how system development would occur if you didn't need to worry about defensive systems... If you then decide to play into the "Rebellion" and "Hard Times" era then these decisions have distinct (and sometimes unpleasant) reprecussions: Imagine the occupants of an agricultural world hit by kinetic strikes so that crops wouldn't grow for a couple of decades. You would know full well that there was enough food in orbit to feed the planetary population for most of a century (destined for shipment to an industrial planet that could build you a ship to get it with) and no way to get it "down"

I'll try to find time to start a thread on system infrastructure, *after* I put the supporting files online... a couple of decades of Traveller have left quite a pile of paper and data files to sort!

Scott Martin
Thread resurrect

I thought I'd summarize all the drop-tank dreck I've dredged up recently from the TML and others, and post the results here for observation.


To fit with those early bits of CT canon, drop tanks appear to be feasible from Day One, in a limited sense, i.e. as demountable external tanks. Prior to TL15, drop tanks could be carried into jumpspace to extend one's range, but they couldn't be used to directly fuel the jump drive.

Improvement came with TL15, apparently with better jump capacitors. It appears that jump capacitors can't hold their charge for long: first, the charge dissipates very quickly, and second, maintaining a continual charge on them must trash them. So perhaps at TL15 the charge could be held just long enough to allow using fuel from the drop tanks. (But: why not be able to use part of the fuel at lower TLs??)

From other discussions, it seems that the jump "fuel" is used up immediately prior to jump -- that's why drop tanks can work -- but the fuel is not converted into energy. Rather, the power plant charges up the jump capacitors, while the jump "fuel" is used to do something related to forming a connection or entry point to jumpspace.

Corporate Use

I'd think that large corporations would jump at the chance to build custom freighters/liners, which would ply the XBoat lanes and major trade routes, essentially carrying 40% more than they could with jump fuel. In other words, it makes them 40% larger for the same price. Very handy, assuming you have a market.

I suspect dedicated short-haul couriers (and liners) for local groups of worlds could also go tankless, or at least with less fuel (say 1 parsec's worth of fuel in case of emergency), thereby freeing up valuable space.
Corporate Example

The canonical example is the Trimkhana-Brilliance, an 800-ton Tukera Liner running on (apparently) 4 drop tanks.

My assumption is that it serves in place of the 1000-ton Arean Lines transport, and with even more capacity. If so, it would require 320 tons of fuel, i.e. four 80-ton L-HYD tanks.

My next assumption is that reusable drop tanks cost approximately the same as a ship hull, i.e. MCr0.1 per ton.

</font><blockquote>code:</font><hr /><pre style="font-size:x-small; font-family: monospace;">(800) Hull MCr 80
14 Bridge -
85 Jump drive-M 160
8 M-drive-M 32
16 Power plant,8ep 32
8 Plant fuel -
-- No internal jump fuel --
52 20 Crew/14 SR 7
400 Pass/100 SR 50
217 Cargo -
Drop Tanks(4x80) 32
MCr 383</pre>[/QUOTE]
LBB5 (Second Ed.) and MT both list Liquid Hydrogen Drop Tanks as "disposable." There is no mention of recovery or reconditioning them for reuse. That would make them exceptionally expensive for commercial use. That could also be the reason that fueling Stations or Jump Gates wouldn't work. As the tanks may be destroyed by the jump field as they are blown free, since they don't have an integral jump drive.
Because of how jump-drive works in MTU, drop tanks must have a jump grid embedded it its 'hull' and the ship's j-drive must be able to supply the neccessary power to it.
Drop tanks without jump-grid are for insystem work...or increases chance for misjump drasticly ( as ship's mass would be half-in/half-out of the jump 'bubble, or whatever you call it )

They also must be built/have internal structure to be able to withstand the maximum G's it's likely to see.
If the tanks have a lower g-rating, then they must be dropped to manuever ( or use agility greater than their G-rating, for people who use that stuff )

...I assume drop tanks have a standardized connection
drop tanks add to total aero drag of ship making atmospheric stuff slower........

MTU uses modded FFS1 and MT rules.
Nice resurrection.

IMTU Drop Tanks find mostly military and crazy-merchant use; based on two house rules.

(1) Drop tank is destroyed once "dropped" prior to entry into jump space. Not too exspensive but still adds cost.

(2) More important from a commercial perspective, use "drastically" increases the chance of misjump (3 in 36), requiring a Nav-4 or better to compensate for. This makes insurance prohibitively exspensive for most commercial ventures and will prveent you from becoming an Imperial certified passenger carrier.
BTL, I have two grades of drop tanks: one is the HG disposable cheapies, and the others are like Shere's, which are essentially small hulls, but are reusable. But good points nonetheless.

Ptah, while forming my opinions of droptanks this week, I also considered the dangerousness of droptanks (1 in 128 chance of jump failure, and half of those are fatal to people), but for the time being decided to not push the issue. I note you have a precedent there in the spectacular failure of the Brilliance.