Alternative to drop tanks

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BigDogsRunning
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Alternative to drop tanks

Postby BigDogsRunning » Tue Apr 23, 2019 1:32 am

Seems like if you have the fittings for drop tanks, you could receive the fuel from another ship if you had nice long fuel hose/tethers. You fuel them up, as they slide into the jump bubble the tethers disconnect and withdraw, so as not to interfere with the jump process. Seems more controlled than drop-tanks.

Freight lines could make use of in-system Jump-Tenders that provide fuel and power using high-capacity tethers to transfer fuel (for jump) and power, similar to drop tanks. They stand off a few km from the cargo ship, connected by tethers. The ship initiates jump, and the tethers drop away, are reeled in, and the ship jumps. Big freight lines could to this on regular routes to greatly increase capacities, and reduce costs.

Obvious use for military ships. They fuel/jump from tenders, and arrive with full fuel tanks.
Condottiere
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Re: Alternative to drop tanks

Postby Condottiere » Tue Apr 23, 2019 1:53 am

External inflatable fuel bladders are probably more viable and closer to the hydrogen turbines.
NOLATrav
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Re: Alternative to drop tanks

Postby NOLATrav » Tue Apr 23, 2019 5:02 am

Also if the tender is larger than the jumping ship, the refueled ship will need to accelerate away from said tender.

Not a big deal I suppose (what’s the 100-diameter distance of a 10,000 dton tanker?) but something to think about.
baithammer
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Re: Alternative to drop tanks

Postby baithammer » Tue Apr 23, 2019 6:02 am

14 m^3 = 1.0 ton
10,000 ton = 140,000 m^3
52m diameter @ 100 diameters = 5.2km distance
DickTurpin
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Re: Alternative to drop tanks

Postby DickTurpin » Wed Apr 24, 2019 7:34 pm

Condottiere wrote:
Tue Apr 23, 2019 1:53 am
External inflatable fuel bladders are probably more viable and closer to the hydrogen turbines.
Collapsible Fuel Tank
Collapsible fuel tanks (also called fuel bladders) are large flexible bladders which expand when filled with
hydrogen fuel. They take up cargo space in a ship and are used to extend range without the need to fit
demountable tanks. Fuel cannot be pumped directly from these tanks to the jump drive, and so a ship
must complete a jump before it can use fuel stored in collapsible tanks.
High Guard, p. 36.
phavoc
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Re: Alternative to drop tanks

Postby phavoc » Wed Apr 24, 2019 8:13 pm

DickTurpin wrote:
Wed Apr 24, 2019 7:34 pm
Condottiere wrote:
Tue Apr 23, 2019 1:53 am
External inflatable fuel bladders are probably more viable and closer to the hydrogen turbines.
Collapsible Fuel Tank
Collapsible fuel tanks (also called fuel bladders) are large flexible bladders which expand when filled with
hydrogen fuel. They take up cargo space in a ship and are used to extend range without the need to fit
demountable tanks. Fuel cannot be pumped directly from these tanks to the jump drive, and so a ship
must complete a jump before it can use fuel stored in collapsible tanks.
High Guard, p. 36.
Storing liquid hydrogen in fuel bladders should be considered "not a smart thing" to do. Liquified hydrogen has to be stored at both a very low temperature and under pressure.

It would be far easier to simply store water in the bladders and run the water through your fuel processor as you shunt it to the fuel tanks. For a ship jumping, your tanks are going to be drained at the time of jump, so you have 7 days to process and fill the tanks. And storing water is easy-peasy with a fuel bladder - far easier and safer than liquified hydrogen. Since the rules allow for a 1-1 ratio, why wouldn't you?
HalC
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Re: Alternative to drop tanks

Postby HalC » Wed Apr 24, 2019 9:02 pm

Phavoc,
I say this half in jest...


You're using too much logic.

;)

At least, that is what my wife tells me.

In any event, I was curious as to how much hydrogen you can crack from 1 liter of water. I thought to myself that I can't possibly be right. So, anyone want to tell me what they think that number is? If I did the math right (and I have to have done it wrong darn it!!!)...

This is what I find elsewhere on the net...

"Water has a rel molecular weight of 18 amu, so 1 mole of water has a mass of 18 grams. So, 1,000 grams of water contains 1,000/18 moles = 55.5 moles. Therefore 1 litre of H2O produces 111 moles of H, and 55.5 moles of O."

Elsewhere I find...


"Avogadro's rule for molar volume states that one mole of any ideal gas occupies 22.4 liters of volume"

If the above mentioned items are correct - to fill 13.5 Kiloliters with Hydrogen, you'd need something like 5 liters of water.

Please tell me the math is wrong. Please?
Moppy
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Re: Alternative to drop tanks

Postby Moppy » Wed Apr 24, 2019 9:23 pm

Liquid hydrogen, not gaseous hydrogen.
phavoc
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Re: Alternative to drop tanks

Postby phavoc » Wed Apr 24, 2019 10:15 pm

HalC wrote:
Wed Apr 24, 2019 9:02 pm
Phavoc,
I say this half in jest...


You're using too much logic.

;)

At least, that is what my wife tells me.

In any event, I was curious as to how much hydrogen you can crack from 1 liter of water. I thought to myself that I can't possibly be right. So, anyone want to tell me what they think that number is? If I did the math right (and I have to have done it wrong darn it!!!)...

This is what I find elsewhere on the net...

"Water has a rel molecular weight of 18 amu, so 1 mole of water has a mass of 18 grams. So, 1,000 grams of water contains 1,000/18 moles = 55.5 moles. Therefore 1 litre of H2O produces 111 moles of H, and 55.5 moles of O."

Elsewhere I find...


"Avogadro's rule for molar volume states that one mole of any ideal gas occupies 22.4 liters of volume"

If the above mentioned items are correct - to fill 13.5 Kiloliters with Hydrogen, you'd need something like 5 liters of water.

Please tell me the math is wrong. Please?
Nope, you aren't wrong. There are actually better ways to store hydrogen (ammonia is one of the best). It's always been one of those Traveller items you don't want to dig too deep (kind of like skimming... how do you separate out hydrogen from helium, oxygen, nitrogen, ammonia, etc while still filling your tanks up going through atmospheres that will have pockets (LARGE ones since we are talking gas giant) of different gases and still fill at same rate.
Moppy
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Re: Alternative to drop tanks

Postby Moppy » Wed Apr 24, 2019 11:38 pm

phavoc wrote:
Wed Apr 24, 2019 10:15 pm

Nope, you aren't wrong. There are actually better ways to store hydrogen (ammonia is one of the best). It's always been one of those Traveller items you don't want to dig too deep (kind of like skimming... how do you separate out hydrogen from helium, oxygen, nitrogen, ammonia, etc while still filling your tanks up going through atmospheres that will have pockets (LARGE ones since we are talking gas giant) of different gases and still fill at same rate.
Sieve according to gas molecule diameter.

I can hand-wave the constant rate of fill if we assume it's an average.

Biggest problem I have with gas giant refuelling is that the radiation Jupiter emits is somehow managable but radiation weapons are so dangerous.
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Re: Alternative to drop tanks

Postby phavoc » Wed Apr 24, 2019 11:54 pm

You'd have to plumb the intakes pretty cleverly to accommodate that and also the ability to do it with water. Airflow at 300 or whatever kph would play merry hell with aerodynamics. May even cause the airflow to create an air wall in the intake and stop most of the airflow.
Moppy
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Re: Alternative to drop tanks

Postby Moppy » Thu Apr 25, 2019 12:01 am

I thought they landed and used a hose for water?

I remember seeing the illustration of a Type S doing that.

edit: Having thought about this for a bit, I'm sure that if you fly fast enough everything's going to get rammed into the intakes somehow and from there either your fuel scoop breaks, or you ram enough gas into the sieve. I don't think airflow disruption is a critical problem like it is in a jet engine.
HalC
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Re: Alternative to drop tanks

Postby HalC » Thu Apr 25, 2019 2:54 am

The specific information on cracking water...

"Hydrogen fuel in Traveller is liquid hydrogen, not hydrogen gas, so 1 dton (14 cubic meters) is actually 1 ton of hydrogen. 9 cubic meters of water weighs 9 tons and can be cracked for 8 tons oxygen and 1 ton hydrogen. "

Got that from a Gent named Anthony over at the SJGames forums. If what he's saying is true (and I have a lot of confidence that he's got it right, he usually does get it right when it comes to that kind of stuff) - then water in its uncracked form is more efficient for storage than Liquid Hydrogen in that it takes up 64.28% of volume that Liquid Hydrogen takes, yet yields 1 dTon of Hydrogen when completed.

So - you want to carry sufficient fuel at hand when you jump into another star system such that you don't have to engage in wilderness refueling, carry your extra fuel in the form of .65 x tonnage necessary in dTons of water. That leaves you with a margin of error equal to about 3% more than you need overall.

Note:
9/14 = 0.6429
9/13.5 = .6667

Perhaps it would be better to use .7 x tonnage to find your Liquid Hydrogen Needs
HalC
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Re: Alternative to drop tanks

Postby HalC » Thu Apr 25, 2019 2:57 am

phavoc wrote:
Wed Apr 24, 2019 11:54 pm
You'd have to plumb the intakes pretty cleverly to accommodate that and also the ability to do it with water. Airflow at 300 or whatever kph would play merry hell with aerodynamics. May even cause the airflow to create an air wall in the intake and stop most of the airflow.
Just out of curiosity - what do you envision the "density" of the atmosphere to be like when engaging in a wilderness refueling operation? If it is on par with the density of the atmosphere a few miles above the surface of Earth, might that change things a little?
baithammer
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Re: Alternative to drop tanks

Postby baithammer » Thu Apr 25, 2019 7:17 am

phavoc wrote:
Wed Apr 24, 2019 11:54 pm
Airflow at 300 or whatever kph would play merry hell with aerodynamics. May even cause the airflow to create an air wall in the intake and stop most of the airflow.
Thrust 1 is equal to 6,000 kph in an atmosphere.
Condottiere
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Re: Alternative to drop tanks

Postby Condottiere » Thu Apr 25, 2019 7:43 am

Alternative to drop tanks
Postby BigDogsRunning » Tue Apr 23, 2019 1:32 am
Seems like if you have the fittings for drop tanks, you could receive the fuel from another ship if you had nice long fuel hose/tethers.

by Condottiere » Tue Apr 23, 2019 1:53 am
External inflatable fuel bladders are probably more viable and closer to the hydrogen turbines.
Moppy
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Re: Alternative to drop tanks

Postby Moppy » Thu Apr 25, 2019 9:24 am

baithammer wrote:
Thu Apr 25, 2019 7:17 am
Thrust 1 is equal to 6,000 kph in an atmosphere.
What does this mean?
AnotherDilbert
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Re: Alternative to drop tanks

Postby AnotherDilbert » Thu Apr 25, 2019 10:14 am

Moppy wrote:
baithammer wrote: Thrust 1 is equal to 6,000 kph in an atmosphere.
What does this mean?
Probably this:
Core, p163 wrote:Spacecraft are capable of any Speed Band listed in the Vehicles chapter, and will typically be going at Hypersonic speeds when entering an atmosphere.
baithammer
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Re: Alternative to drop tanks

Postby baithammer » Thu Apr 25, 2019 12:43 pm

AnotherDilbert wrote:
Thu Apr 25, 2019 10:14 am
Moppy wrote:
baithammer wrote: Thrust 1 is equal to 6,000 kph in an atmosphere.
What does this mean?
Probably this:
Core, p163 wrote:Spacecraft are capable of any Speed Band listed in the Vehicles chapter, and will typically be going at Hypersonic speeds when entering an atmosphere.
Makes scooping a bit more reasonable as that speed allows a lot of space to be covered in a short amount of time.
phavoc
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Re: Alternative to drop tanks

Postby phavoc » Thu Apr 25, 2019 1:05 pm

I've never agreed with the space ship speed listing. It's crazy way too high. An object traveling at such speeds needs to be aerodynamic and Traveller ships aren't. If you want to crash that's a fine speed. Otherwise it's completely unrealistic.

And skimming? Impossible at that speed with the designs. Try driving at 70 and stick your hand out perpendicular (flat) to the ground. Instant speed break. Skimming requires airflow into the fuel tanks through baffles, pipes, etc. It's all incoming though, and your air intakes have to sip the air or else the pressure in the tanks will create a pressure wave at the opening and literally create a wall of air that will prohibit more air from coming in. And this is at far lower speeds. The higher your speed is the higher the pressure to block air.

Spaceships are optimized for space. They should never have the need to travel at multi Mach numbers. It's far more likely if you lopped off a bunch of zeroes and had the spacecraft traveling at a hundred kph per G rating. Interface craft, since they are designed for it, could be double the normal rate. That's a reasonable number and still makes for a quick journey GTO or OTG. It also makes your aerospace vehicles designed for the atmosphere to be superior if you have combat or whatever.

Vehicles propelled by grav should have an upper limit on their speed, leaving good ol fashioned air breathing engines and aerodynamic structures superior in atmo.

Just as an aside, those grav bikes you see with the high kph ratings and just an windshield up front? Yeah, you ain't gonna be able to stay on it at 600kph. Wind forces will tear you right off of it. Humans don't have the strength to hold on. Even in battlearmor you would be challenged at higher speeds, and the airflow would be lifting your body off the cycle as your suit became a lifting body at the higher speeds.

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