Flexible Far Traders?

[Condottiere]

Starships: Bunkerage and the Oukhaha class

I'm sort of clueless as to how this works, you'll have to get the author to clarify how this functions with collapsible fins and fuel bladders.

Unless ...

 

[baithammer]

The Collapsible Fuel Tank is pretty much just the bladder itself, which when empty takes up very little space. ( Yes, real physics would be difficult to model.)

The FUEL/CARGO CONTAINERS are conformal container that allows access ways to be used while still using the cargo space, basically tuperware of different sizes to better fit the cargo space.

 

[AnotherDilbert]

Getting fuel out of the bladder is easier than pumping out of a fixed fuel tank, you just constrict the bladder. It's a big balloon. You just start reeling in the restraining net and sploosh, all your LHyd goes squirting out the giant nozzle into the power plant, or through a giant heater/vaporizer to inflate your Jump Bubble.

If you press too hard the LHyd turns into solid hydrogen ice and refuses to come out.

To get the LHyd out very fast you need very high pressure or a very large hole (or both). Very high pressure does not work with LHyd. A very large hole and the pipes to connect them to the jump drive would show up on the deck plans, but are absent on most deck plans.

 

[AnotherDilbert]

If you want to transport 100 - 1000 m³/s (to empty the tanks of a starship in a few minutes) ...

The LOX pump in the F-1 rocket engine in the Saturn V pumped about 1.5 m³/s ...

The LOX pumps for the F-1 engines on the Saturn 5 could pump 94,000 liters of LOX per minute.

94000 litre/minute = 94 m³/minute ≈ 1.5 m³/second.

The space shuttle main tank had 380,000 gallons of LHyd, and it could be filled in under 3hrs. The main lines were 17" in diameter (for both LHyd and LOX).

The shuttle fuel pump delivered less than 1 m³/s.

 

[AnotherDilbert]

Collapsible Fuel Tank ...

FUEL/CARGO CONTAINERS ...

Neither can independently fuel a jump drive and which is borne out by the mechanics presented.

The author seems to disagree:

The intent was that they function just like regular fuel tanks when filled with fuel.

 

[phavoc]

94000 litre/minute = 94 m³/minute ≈ 1.5 m³/second.

That's 7 Dton's/minute. And that's a single pump that is not all that big. It is entirely possible to add more fuel pumps/lines to quickly transfer fuel. But the bigger question is what's being done with the fuel? If there are going to be problems quickly pumping it, then there are surely going to be problems either fusing it or converting it into exotic particles.

The shuttle fuel pump delivered less than 1 m³/s.

I couldn't find the fuel rate of the SSME, but I did find NASA's blurb about the fuel burn rate. The pumps burn about 40,000gal in 25 sec (1,600 gallons/sec, or 6,056 Liter/sec, or 6 cubic meters/sec). If I did my math correctly (6 cubic meters/sec * 60 = 360 cubic meters/minute. Divide that by 13.5 and you get about 27 Dtons/minute. That's a pretty healthy pumping rate.

 

[M J Dougherty]

The idea behind cargo/fuel modules was that they are built at new design rather than converting odd spaces of fuel tank to cargo holds. You build a standard shaped cargo area with extra thick bulkheads and plumbing connecting it to the fuel system. When in use as a fuel tank, the space is part of the fuel system. When not, it is available to carry cargo. The plumbing is where you lose the tonnage.

There was never any intent that you would suddenly be able to jam cargo containers into wing tanks on a Subsidised Merchant or anything like that.

 

[Condottiere]

Water, wine and beer flavour is enhanced with human waste products. And anti-freeze.

Not so sure about petrochemicals and liquid hydrogen.

I would imagine turning it back to a cargo hold would require strong cleanser.

 

[heron61]

Water, wine and beer flavour is enhanced with human waste products. And anti-freeze.

Not so sure about petrochemicals and liquid hydrogen.

I would imagine turning it back to a cargo hold would require strong cleanser.

Why? Hydrogen is exceptionally volatile, and the best starship fuel is exceedingly pure hydrogen. It seems to me that a method of opening the tank to vacuum would be all that's needed. Vent the tank to vacuum, wait a few minutes, and you have a spotless tank (at least if you're using refined fuel) waiting for cargo to be loaded in once you land. OTOH, unrefined fuel could contain small amounts of all manner of complex and potentially problematic chemicals and would likely require special cleaning.

 

[BigDogsRunning]

Water, wine and beer flavour is enhanced with human waste products. And anti-freeze.

Not so sure about petrochemicals and liquid hydrogen.

I would imagine turning it back to a cargo hold would require strong cleanser.

Why? Hydrogen is exceptionally volatile, and the best starship fuel is exceedingly pure hydrogen. It seems to me that a method of opening the tank to vacuum would be all that's needed. Vent the tank to vacuum, wait a few minutes, and you have a spotless tank (at least if you're using refined fuel) waiting for cargo to be loaded in once you land. OTOH, unrefined fuel could contain small amounts of all manner of complex and potentially problematic chemicals and would likely require special cleaning.

Wouldn't exposing the vast majority of those sorts of chemicals to vacuum boil them off?

 

[AnotherDilbert]

Let's make an attempt at a Flexible Far Trader...

TL12, 200 Dt, J-3, M-3, MCr 60.
4 Crew, 10 Passengers, 9 Low, 8 Dt cargo.
Partially streamlined with external cargo mounts and drop tank collars.
The only luxury is a hydroponic garden as a part of the passengers common area.

The internal fuel tankage is in Fuel/Cargo Containers, so we can add 20 Dt cargo for each J-1 we forego.
J-3: 08 Dt cargo
J-2: 28 Dt cargo
J-1: 48 Dt cargo
J-0: 68 Dt cargo

We can also add external cargo and/or fuel:
J-3: No external (partial streamlining, can land).
J-2: 50 Dt drop tank (retained): 68 Dt internal cargo (partial streamlining, can land)
J-2: up to 100 Dt external cargo/fuel, unstreamlined
J-1: up to 400 Dt external cargo/fuel, unstreamlined

 

[AnotherDilbert]

Let's look at the economic potential (here potential is the profit if the ship is filled to capacity):

J-3:

J-2:

J-1:

As we can see it's not so good to make short jump while still paying the mortgage for the large jump-drive.

 

[AnotherDilbert]

And with external fuel and/or cargo...

J-2 with drop tank (retained):

And of course if we add external cargo profitability improves considerably:
J-2 with 100 Dt external:

J-1 with 400 Dt external:

 

[BigDogsRunning]

And with external fuel and/or cargo...

J-2 with drop tank (retained):

And of course if we add external cargo profitability improves considerably:
J-2 with 100 Dt external:

J-1 with 400 Dt external:

Great analysis AnotherDilbert!

The external cargo haulage is where the action is for the short hops. But, for small operators, the ability to take whatever loads are available for short, or longer jump deliveries, would seem to create massive advantages in a game environment that may not be as predictable.

 

[steve98052]

As I see it, the differences between regular fuel tanks, and cargo-fuel spaces, and collapsible fuel tanks are:
- regular fuel tanks are designed in, good only for fuel, including jump
- cargo-fuel spaces are designed in, good for fuel or cargo, including jump fuel
- collapsible fuel tanks are a cheap retrofit, allowing fuel to be stored in cargo spaces, but lacking the necessary designed-in high-speed pumps required for use as jump fuel

So what if you acquire an old beater of a merchant starship with a jump drive so past due on maintenance (or damaged) that it's better sold for scrap and replaced than repaired in place? In that case, a merchant with the right routes in mind might replace it with a Jump-3 drive, and overhaul the cargo hold to serve as convertible cargo-fuel space, and have a Jump-3 -2 -1 ship when the old beater comes out of the shipyard rebuilt as a classic hot rod.

Point is, the reason collapsible tanks don't work for jump fuel is that they're too cheap for that. They're also removable, so you could sell them to Dirty Dick's Starship Accessories -- or hide them on some inconspicuous asteroid -- if you decide you don't need them for a long enough time that it's worth having a little extra space in the hold that it would take to carry them around collapsed.

 

[AndrewW]

- regular fuel tanks are designed in, good only for fuel, including jump

Well, there are Concealed Compartments that hide in the fuel.

 

[AnotherDilbert]

As I see it, the differences between regular fuel tanks, and cargo-fuel spaces, and collapsible fuel tanks are:

Agreed.

So what if you acquire an old beater of a merchant starship with a jump drive so past due on maintenance (or damaged) that it's better sold for scrap and replaced than repaired in place? In that case, a merchant with the right routes in mind might replace it with a Jump-3 drive, and overhaul the cargo hold to serve as convertible cargo-fuel space, and have a Jump-3 -2 -1 ship when the old beater comes out of the shipyard rebuilt as a classic hot rod.

The problem is that a J-3 drive is about half the cost of a trader. Refitting an old ship would cost almost as much as buying a new ship, and you would end up with a beat up old wreck with a gleaming new jump drive. It would be faster than waiting for new production though...

Major refits cover changes in power plant, manoeuvre or jump drive, as well as changes to spinal mounts or launch facilities (such as launch tubes). Removing these components costs 0.5 times the cost of the original system, while removing them and then installing new ones costs 1.5 times the cost of the new system. The time this takes is one quarter of the time required to build a new ship of the same size.

It might take Referee dispensation and extra cost to increase the engineering compartement.

Those items covered under a major refit cannot be increased in size though they may be reduced.

 

[steve98052]

The problem is that a J-3 drive is about half the cost of a trader. Refitting an old ship would cost almost as much as buying a new ship, and you would end up with a beat up old wreck with a gleaming new jump drive. It would be faster than waiting for new production though...

In that case, it might only make sense on a newish ship where the engineering section is damaged into scrap, but the rest of the ship is in good condition.

The retrofit rule is a complication too. I could see freeing space in engineering by relocating the power plant to an engineering annex (formerly allocated as hold), but a purpose-built ship would probably be a better idea.

 

[Condottiere]

I think the manoeuvre drives require specific engineering compartment, both to tie them down and to balance propulsion.

The power plants, probably not a necessity, though I suspect there would be some discomfort with fission reactors.

Outside of attaching the fuel lines to it, someone should try free floating the jump drive and see what happens.