General Drop Tank Tender?

[mike wightman]

The wiki on Drop Tanks explains it pretty well under Drop Tank Operations.

Drop Tank - Traveller

wiki.travellerrpg.com

The wiki is wrong, at least in the Third Imperium.

We have a TAS News item that explains the drop tanks are destroyed when dropped.

L-Hyd drop ships have only been in service for the last dozen years in the
interior, being made possible by recent advances in the field of capacitor
engineering, a joint press release explained. Commercial vessels equipped with the
new generation of long-storage jump capacitors carry jump fuel in specially
designed L-Hyd drop tanks in excess of their rated tonnage. Upon conversion of the
fuel to the massive energy required for jump, the drop tanks are explosively
jettisoned through the use of break-away connections and explosive bolts. Jump is
executed when the remains of the tanks are a safe distance from the vessel.

L-Hyd drop tanks are not reusable, and thus increase the absolute cost per
jump. However, experience has shown that the increase in cargo tonnage resulting
from the elimination of internal J-fuel storage more than makes up for this, the
press release explained.

I re-iterate my earlier comments, if drop tanks are reusable then you should be able to put an engine on them to make them self recover, in which case build a fuel tender and remove the need for merchant ships to carry internal jump fuel.

 

[Spinward Flow]

Upon conversion of the fuel to the massive energy required for jump, the drop tanks are explosively jettisoned through the use of break-away connections and explosive bolts. Jump is executed when the remains of the tanks are a safe distance from the vessel.

Jettisoned
Break away connections
Explosive Bolts

Jump when a safe distance

L-Hyd drop tanks are not reusable

To be fair ... when L-Hyd Drop Tanks were introduced to Traveller in the early 80s, the notion of reusability in rocketry was considered something of a pipe dream.
Rockets were expendable only ... so why shouldn't drop tanks be expendable only also?

NASA's Space Shuttle was "reusable" ... after almost 6 months of refurbishment after each mission (not exactly a quick turnaround time there!) ... but the Main (drop) Fuel Tank was EXPENDED after every launch ... so why shouldn't drop tanks be expendable also?

Of course, with Falcon-9 demonstrating that propulsive recovery of craft is not only possible(!) ... but reusability is what reduces costs due to dispensing with "disposable" assets and moving to a business model of "expend only when necessary" is the way to go for a commercial operation ... the way people think about these questions has changed.

This is just one of those cases where someone simply needs to Build A Better Mousetrap™ (so to speak) ... in order to enable an entirely different business model of operations.

 

[Condottiere]

I think it depends, on how drop tanks are actually constructed, and that may vary.

So, they could be constructed with a bridge, hard points, and manoeuvre drives, and disconnects once the fuel is completely transferred to the internal fuel tanks.

 

[mike wightman]

You don't need to transfer the fuel to internal tanks, fuel from drop tanks is used directly.

And if drop tanks can be recovered that means you could just use a hose to the jump ship from a tender to provide the jump fuel.

Re-usable drop tanks have unintended consequences that change the setting.

 

[Condottiere]

Bandwidth.

Probably cheaper to have the hoses run to the tanks.

You try doing that a hundred diameters away, within six minutes.

 

[mike wightman]

The distance doesn't matter - if you can transfer the fuel from a drop tank to a ship you can build a pump/hose that can transfer at the same rate.
If the drop tank can make it to safety and thus be reused then a m6 ship with a hose will have no difficulty

 

[Condottiere]

Hundred tonnes minimum; jump factor one.

Sphere fourteen hundred cubic metres.

1'388 centimetres diameter.

Times a hundred, one kilometre, three hundred and eighty eight metres.

So you would need about a one and a half kilometre hose and plumbing, with enough suction and power to transfer a minimum of a one hundred forty thousand litres, depending on edition and accounting for the need to process the fuel within the jump drive, say three minutes, in a thin enough hose that wouldn't effect the transition.

 

[mike wightman]

No, you need an elasticated hose 1km long that can be withdrawn very quickly as the tender moves to safe distance.

If a pump and conduit can transfer the fuel from a drop tank through the jump engine or whatever then you can attach a hose rather than a drop tank.

 

[whartung]

This big thing regarding fuel tenders is that they likely are only really relevant to that large commercial sector. The military, scouts, free traders, etc. would not use these.

So this is a good reason as to why they're not really discussed much in literature. They just don't really impact normal Travelling kind of stuff.

but, that said, for background, if it were possible, I think it would be common in large trade areas with regular, large ships moving cargo and passengers.

 

[TamsinP]

No, you need an elasticated hose 1km long that can be withdrawn very quickly as the tender moves to safe distance.

If a pump and conduit can transfer the fuel from a drop tank through the jump engine or whatever then you can attach a hose rather than a drop tank.

Hmmm, a hose which retains its elasticity after tens of tonnes of liquid hydrogen (at -253C) have passed through it?

Interesting, interesting...

 

[bookwyrm]

You could split the difference... the lower tech drop tanks are NOT reusable while higher tech drop tanks are. The Question then becomes; at which tech level does this change happen?

After considering it for a bit, I seem to remember reading that Drop Tank Technology is TL 15???

 

[TamsinP]

After considering it for a bit, I seem to remember reading that Drop Tank Technology is TL 15???

Looking back at the very first TNS piece in JTAS #02, they were being manufactured by General Shipyards at Pixie which is TL13. It probably does depend on which version of Traveller though.

 

[Condottiere]

There's got to be more going on, than just the simple transfer of fuel.

Otherwise, you could take the fuel bladder, fill it up with hydrogen, place it on top of the starship, let the jump drive suck it dry.

It collapses to one percent of volume, which would be likely less than a half percent of volume, and you might tune the jump drive to compensate, and off you go.

 

[mike wightman]

High Guard 79 lists them as TL 12

L-Hyd Tanks: Disposable fuel tanks which are fitted outside the ship, and drop away before jump. The result is more interior space available for cargo and passengers. Cost: Cr 10 000 plus Cr1000 per ton of fuel. Usable only with jump drives if a special high capacity accumulator is installed (tech level 12; Cr500 000).

 

[Condottiere]

Didn't seem to survive to Mongoose.

Not to forget, that you can't feed the fuel from the bladder directly to the jump drive, and that's internal; indicates that flow through probably is an issue.

 

[TamsinP]

Didn't survive to LBB5(80) - no minimum TL mentioned there, nor any mention of special high capacity accumulators being needed. Also no mention in LBBA5 where collapsible and demountable tanks are added to the fuel tankage options.

 

[whartung]

Otherwise, you could take the fuel bladder, fill it up with hydrogen, place it on top of the starship, let the jump drive suck it dry.

You could, but such a bladder would likely not have the structural integrity necessary to, at a minimum, quell the momentum of the fuel contained, even if the ship itself does not move. In fact, the ship would not likely not accelerate once the bladder begins to fill, or after.

That said, the idea of a structurally sound "external fuel" facility may be worth exploring. Even it if reduces down to 10% of the tankage, its a win.

But then there's the matter of stowing it properly during drainage so that it is, indeed, ready to jump when the time comes.

For example, I would submit that you couldn't use such a facility for wilderness refueling. It would be too rough. While the external bladder has some integrity, it's not enough to withstand the jolt of skimming, atmosphere, or even liftoff.

But if you're plugged into a high port, and give a few pulses of the M-Drive to get out to 100D, say .1, .2G, maybe it could work.

 

[Condottiere]

In theory, there's got be a reason for all the extra plumbing for the drop tanks.

As regards the balloon, it's been part of the rules that you can't tap directly into the jump drive with it, even through the normal tanks, so that sort of indicates that a kilometre long hose isn't going to work, either.

 

[mike wightman]

Drop tank fuel goes directly to the drive.

If drop tanks are recoverable there is no reason to use anything but.

The next step is to have a self recovering drop tank.

Once you have a self recovering drop tank you have changed the setting.

 

[Spinward Flow]

Once you have a self recovering drop tank you have changed the setting.

Only at type A/B starports.
At type C-X starports ... not so much ... and those are the majority of starports you're going to find on any sector map (using LBB3 world generation).