Expandable fuel tank

[JAFARR]

This is sort of an extension of the collapsible fuel tank from MT. Suppose the wall of your fuel tank has a movable section that will expand into the cargo bay. If you need extra fuel for a part of your trip, you empty this tank into another, release that wall section, expand it into your (empty) cargo bay and hydraulically lock it into the new position. This wall section would have a sealing device that was sealed at the same time the hydraulic lock was activated.

Advantages over collapsible tankage is that fuel can be used directly from the tank without the necessity of transferring it to the main tanks.

The flip side is it requires 1% of the expanded tankage with a 1 ton minimum for the operating mechanism.

It also requires a minimal amount of protection for the sealing surface that is exposed when the tank is not expanded. A protective cover which has to be removed before use, and sealing area must be inspected/repaired before use.

(1) Roll 2D6.
(2) Roll of 12 requires second roll for amount of damage to surface.
(3) Roll D6.
(4) 1, 2, 3 requires 1D6 minutes of work with common hand tools.
(5) 4 or 5 requires 1D6 hours of work with same tools.
No second inspection roll is required for #4 or #5 above.
(6) 6 requires 1 day of labor followed by another 2D6 roll.
(7) 1 - 11 means repairs were successful.
(8) 12 means another day's work with portable machine tools found in any class C+ starport.
(9) Eng 3+ or mech 3+ allows follow up roll to take place immediately following #6 instead of after the one day of labor. (They can look at the damage and realize it will take the extra work without having to spend the time trying to fix it first.)

 

[boomslang]

Advantages over collapsible tankage is that fuel can be used directly from the tank without the necessity of transferring it to the main tanks.

Given the speed with which Jump drives suck down their fuel to initiate jump, anything flexible enough to compact into the desired storage space yet robust enough to take the sudden load strain is not likely to be cheap.

Interior Demountable Tanks are rigid for this reason, I expect.

There are also issues of rapid pressure equalization; unless the Hold is already in vacuum and/or you have the interior bulkheads already sealed at the moment of truth, you risk a dangerous partial decompression of the entire Main Compartment when the J-drive puts the Big Suck on the Fuel Bladder. The bends are not a pretty thing...

I have never had any operational issues with any of the alternative tanking types; can you provide more scenario details of the problem you are proposing to solve?

 

[atpollard]

The rules have always overlooked the most obvious solution ... build compartments that can be used to store either cargo or liquid hydrogen. A fuel tank with a cargo door could serve either function (cargo or fuel) just not at the same time.

So just design the ship with multiple 10 ton cargo/fuel tanks (but don't forget which is currently being used for which). No 'internal tanks', no 'flexible membranes', no 'moving walls' ... just tanks with doors for fuel or cargo.

 

[Gadrin]

GURPS Traveller offers such a system...

COLLAPSIBLE TANKS
A 400,000-gallon collapsible self-sealing tank made of
light folding polymers, this expands into an empty Hold or
Spacedock module (which are required, to provide support
and stability). It holds 120 dtons (and only 120 stons) of fuel
when full. It can be installed in half-sized increments. A full
tank will rupture and spill during maneuvers at least 1.5 G
greater than that compensated by the utility systems.

Fuel from collapsible tanks must be pumped into the
normal fuel tanks before it can be used; thus, a jump made
with collapsible tanks may not use more fuel than the capacity
of the normal interior fuel tanks. Pumping fuel before a
jump takes about three hours. A typical use for collapsible
tanks is to allow a short-jump ship to cross a long-jump
“gap” in two or more jumps.

>

 

[far-trader]

If I recall correctly Collapsible Tanks require 5% of their volume for storage while Dismountable Tanks require 20%. I forget the costs offhand. From this I designed my own version of your idea if I read your intent correctly, calling them Accordion Tanks (or something ).

My version cost the same as both Collapsible and Dismountable tanks and took up the combined volume when stored as well (25% iirc). But they allowed both the ready fuel use as per Dismountable tanks and the fast storage or refilling or Collapsible tanks.

When used internally they aren't much of a benefit, unless you use the volume opened up for simple recreation or extra hanger volume for repair and maintenance.

Where they really were meant for in MTU was externally. Allowing the function of drop tanks (more fule, less ship) without the hazard and loss of drop tank seperation. So you could use them for jump fuel, extending your range without carrying the fuel, and not worry about the increased chance of misjump. Multiple times since you don't leave them behind.

 

[far-trader]

...It also requires a minimal amount of protection for the sealing surface that is exposed when the tank is not expanded. A protective cover which has to be removed before use, and sealing area must be inspected/repaired before use.

Just have them retract into a hatch sealed area. No fuss no muss

 

[JAFARR]

Clarification

Ever see a bank vault door when it is open? Naval personal ever see a hatch through an armored deck? Both of them seal on a tapered surface with some type of cam/cam operated locking device. In the case of bank vaults, it is pin about 2 inchs in diameter that are pushed into a hole in the door frame by the action of a cam. The door is about 8 inches thick and due to the taper, the seating surface is about 12 inches wide.
I was thinking of a wall about 8 to 12 inches wide with a locking bar 3 to 4 inches wide that will protrude out from the center of the wall 3 to 4 inches into a locating/locking groove in the fixed structure when locked and is completely with drawn into the mobile section of tank wall when being moved. When not being used, the seating area for the expanded position will have a protective insert installed to protect the sealing surfaces.

Making it massive enough to prevent boomslang's "big suck" problem is not a problem. That and the operating mechanism to move it is what requires the 1 ton mimimum size. The reason for the damage inspection rolls is that no matter how careful you and the crew are in handling it and the expanded seating area, there is still a chance of incidental damage. We are dealing with a gas tight seal, not a liquid tight seal. Gas sealing surfaces are less tolerant of flaws.

 

[JAFARR]

If I recall correctly Collapsible Tanks require 5% of their volume for storage while Dismountable Tanks require 20%. I forget the costs offhand. From this I designed my own version of your idea if I read your intent correctly, calling them Accordion Tanks (or something ).....

MT says collapsible tanks don't use any space when collapsed. (non-bladder type Dismountable tanks require their full volume because they are basically a tank inserted into the cargo hold. I don't know about any of the later versions.

 

[far-trader]

...We are dealing with a gas tight seal, not a liquid tight seal. Gas sealing surfaces are less tolerant of flaws.

Ah, but it's not a gas is it? Isn't it LH2? A pressurized cryogenic liquid, requiring it's own special insulation and such.

 

[far-trader]

MT says collapsible tanks don't use any space when collapsed. (bladder type Dismountable tanks require their full volume because they are basically a tank inserted into the cargo hold. I don't know about any of the later versions.

Yeah, probably picked it up in T4 or TNE. I think T20 tagged a volume on it too. Or I could be misremembering

 

[JAFARR]

Ah, but it's not a gas is it? Isn't it LH2? A pressurized cryogenic liquid, requiring it's own special insulation and such.

Which also needs to be treated with extra care just like a gas sealing area IMHO.

 

[JAFARR]

Another thread refers to rules clarifications in TCS. I just checked it out and it states that collapsible tanks take 1% of volume when collapsed. That seems like a reasonable amount to me.