Crossing Empty Hexes In A J1 Ship

[MarianLH]

This may be a dumb question, but is there any reason why a jump-1 ship (like a Type A) couldn't carry some extra fuel in its cargo bay, and make a second jump? Sort of like an internal drop tank?

I really like the Beowulf class, but looking at starmaps, it seems that no matter where you start, it can't go very far before running into an empty hex.

 

[HG_B]

This may be a dumb question, but is there any reason why a jump-1 ship (like a Type A) couldn't carry some extra fuel in its cargo bay, and make a second jump? Sort of like an internal drop tank?

I really like the Beowulf class, but looking at starmaps, it seems that no matter where you start, it can't go very far before running into an empty hex.

It's done all the time. Collapsible fuel tanks. Filled with H2O it only takes ~60% of the volume LHyd does (you need a fuel purif plant though).

 

[MarianLH]

Filled with H2O it only takes ~60% of the volume LHyd does.

I'm confused. How could water take up less volume than pure hydrogen? Or is the difference due to liquid hydrogen needing bulkier storage equipment?

ETA: Also, where are collapsible fuel tanks discussed in the CT rules?

 

[rancke]

This may be a dumb question, but is there any reason why a jump-1 ship (like a Type A) couldn't carry some extra fuel in its cargo bay, and make a second jump? Sort of like an internal drop tank?

Only economics. A jump-1 ship carrying cargo two jumps is costlier (per unit carried) than a jump-2 ship (and takes more time). A jump-1 ship reducing its cargo capacity by carrying fuel for an extra jump has an even higher per unit cost. It's just not competetive.

There's a lot more space between hydrogen atoms than between water molecules. You pack the hydrogen in much tighter if you carry it attached to oxygen. Using water that way is contrary to canon, incidentally, but no one has been able to figure out any remotely plausible reason why it shouldn't be perfectly possible.


Hans

 

[aramis]

I'm confused. How could water take up less volume than pure hydrogen? Or is the difference due to liquid hydrogen needing bulkier storage equipment?

Liquid hydrogen has a peak mass of about 0.075 tons per cubic meter. (density of 0.07)

Water has a peak density of 1.04 tons per cubic meter (under high pressure and at 4°C) and is nominally 1 ton per cubic meter (density 1). It's also comprised of 1/9th hydrogen by mass... for an effective density of 0.11 hydrogen, at penalty of .89 tons of oxygen you have to haul.

Since traveller drives are usually figured by volume, not mass... it leads to some interesting wonkiness like the assertion of carrying more hydrogen by carrying it as part of water.

ETA: Also, where are collapsible fuel tanks discussed in the CT rules?

See Trillion Credit Squadron (p.13-14).

TCS includes [interior] collapsible, [interior] demountable, exterior demountable, and drop tanks at those pages.

(The Traveller Adventure includes demountable tanks on page 44)

 

[Xerxeskingofking]

This may be a dumb question, but is there any reason why a jump-1 ship (like a Type A) couldn't carry some extra fuel in its cargo bay, and make a second jump? Sort of like an internal drop tank?

I really like the Beowulf class, but looking at starmaps, it seems that no matter where you start, it can't go very far before running into an empty hex.

none. nothing stops you designing a J1 ship with 20% fuel storage (i.e. enough for two jumps) as standard. all you need for a stock beowulf to tranfer fuel form a tank in the cargo hold to the main tanks is a length of hose. looking at the deck plans, you could site the tank at the rear of the cargo bay and, either assuming a pipe to the fuel tanks is installed thier or that you install one, you could pipe the fuel into the mian tanks the moment you enter jumpspace. failing that, when in realspace you could vent the hold, go EVA and feed teh fuel into the tanks via the skimmers and purifiers, agian, a linkage to the cargo hold could be installed to allow you to jump, then refine the fuel while in jump. thus, a ship could jump, refine in jump, pop out of jump in deep space (or a system edge), then immidatly begin to plot it's next jump.

I think lower tech socities would do that a lot more than higher tech ones. The one jump fuel set up makes sense when dealing with developed space, with well mapped fuel scorces and a few parsecs leeway, but with a J1 craft, especially in a "early days" situation where you are not too sure wether there is a fuel scorce at the end of the jump, i'd say it makes more sense to have a return trip already in the tanks so that you have explore a system with the knoweldge that you can get back without needing to find fuel in the wild.


also, if J1 is all you have, then you have to simply work with the tools you have and take what advantage of thier properties as you can. the extra reach advantage would, IMO, lead to J-1 ships with fuel to 2 ro even 3 jumps in them, allowing them to reach across the voids between clusters, linking groups of worlds.

 

[abomination]

I think there's an economic argument for service stations in the gaps along J1 routes between major worlds.

Naturally, everything would be at a premium cost as it has to be imported & there is no other choice.

There might be a good adventure set in a deep space Watford Gap.

 

[rancke]

I think there's an economic argument for service stations in the gaps along J1 routes between major worlds.

Not if the civilization has access to jump-2 technology. It's both cheaper and faster to use a jump-2 ship to cross a 2 parsec gap. So there won't be any regular jump-1 traffic to use the way station. Only the occasional free trader and regular trader shifting from one route to another.

It's a nice idea, but it doesn't fit the technological underpinnings.

What might work is a way station that turns a 3J2 route into a 2J2 route, and similar savings for jump-3 and jump-4 routes.

EDIT: Example: Traffic between Dodds (SM 2739) and Trin (SM 3235) requires two jump-3 and one jump-1 (plus going through amber-zoned Hazel (SM 3236)). Alternatively one jump-2 and two jumps-3 through Robin and Hammermium. A way station in 3037 (serviced from Tee-Tee-Tee) would allow the trip to be made in two jumps-3. That might make economic sense (I haven't run the numbers and I'm not quite sure how to calculate the expenses) and it certainly is faster than the more conventional routes.​

Hans

 

[MarianLH]

Thanks for all the help!

 

[HG_B]

There's a lot more space between hydrogen atoms than between water molecules. You pack the hydrogen in much tighter if you carry it attached to oxygen. Using water that way is contrary to canon, incidentally, but no one has been able to figure out any remotely plausible reason why it shouldn't be perfectly possible.


Hans

Actually, it isn't contrary to cannon at all. The authors jut didn't remember their high school chemistry so didn't think to include it. It isn't disallowed anywhere in any rule in Travelling.

 

[rancke]

Actually, it isn't contrary to canon at all. The authors jut didn't remember their high school chemistry so didn't think to include it. It isn't disallowed anywhere in any rule in Travelling.

I'm pretty sure the canonical example in TTA has the PCs install 20T of demountable tanks to carry 20T of extra fuel (I can't be bothered to check right now). There's only one reason why they would do that; to wit, that for some reason water won't do. "There's no rule for it" doesn't necessarily mean "It can't be done", but it does imply that for some reason it's not done often enough to warrant a rule for it.

Just to be clear: I think introducing such a rule would be a really good idea.


Hans

 

[HG_B]

I'm pretty sure the canonical example in TTA has the PCs install 20T of demountable tanks to carry 20T of extra fuel (I can't be bothered to check right now). There's only one reason why they would do that; to wit, that for some reason water won't do.

No. The only reason to do that is because the author didn't know his chemistry. Has ZERO to do with water. Unless, you're saying that cannon prohibits chemistry now? If that is the case, you can't skim water to get Hydrogen fuel...

 

[rancke]

No. The only reason to do that is because the author didn't know his chemistry. Has ZERO to do with water.

That's a meta-reason. That has zero to do with the in-game reality. The in-game reality (until and unless retconned) has people carrying around spare fuel in the form of liquid hydrogen rather than water. That's a stone cold in-game fact. One that I wouldn't mind seeing retconned, but while it remains un-retconned, it is evidence that for some ineffable reason water is generally not used to carry spare fuel.

Unless, you're saying that canon prohibits chemistry now? If that is the case, you can't skim water to get Hydrogen fuel...

The rules specifically say that you can skim water to get fuel.


Hans

 

[aramis]

The explanation for the water not being used is in FF&S... T-plates are calibrated for not more than 10Tons(= megagrams = Mg) per Td (14kl); carrying fuel as water pushes that real hard, and strongly limits other, heavier assets... like weapons, armor, and cargo.

Carrying 1Mg of Hydrogen is roughly 14kL, leaving 9Mg for that Td for use in other Td's.
Carrying 1Mg of Hydrogen in water is 9kL, but uses also 9Mg total of the 10 allotted for the Td, leaving 5kL free but only 1Mg free...

The abstractions of CT design ignore mass as presumed to be under that relative limit.

 

[Antony]

Of course your fuel purification plant does include an electrolysis function doesn't it? So if water is not directly suitable for the jump drive you electrolyse it producing hydrogen for the power plant/drives and oxygen for life support, excess vented into space.

 

[warwizard]

IMTU I use 99% of the H2 "jump fuel" as a cryogenic heat sink and for inflating the jump bubble quickly, don't have time to convert 2 H2O to 2 H2 + O2 to inflate the jump bubble and need someplace to put the O2 that's generated, as pumping it into the jump bubble would make for a potientially explosive atmosphere in the jump bubble.
Instead of just H2O, perhaps we could carry liquid methane CH4, that's 25% hydrogen by weight. methane properties 422.62 kg/m3 *.25 = about .105 tons H /m3 or nearly the same volumetric efficiency of water at a lower mass.

 

[rancke]

The explanation for the water not being used is in FF&S... T-plates are calibrated for not more than 10Tons(= megagrams = Mg) per Td (14kl); carrying fuel as water pushes that real hard, and strongly limits other, heavier assets... like weapons, armor, and cargo.

Yes, that's an obvious explanation, but it ignores the possibility of installing more thrusters. This may not be commercially sound, but there are certainly times where you'd be willing to make such a trade-off, e.g. rift-crossing couriers, tankers. Or just accepting that you'll be maneuvering at 0.5G instead of 1G...

The abstractions of CT design ignore mass as presumed to be under that relative limit.

And a reasonable abstraction it is too. But it's one of those "the rules don't take it into account because it's usually not done, not because it's impossible" rules I've mentioned in another thread.


Hans

 

[rancke]

Of course your fuel purification plant does include an electrolysis function doesn't it? So if water is not directly suitable for the jump drive you electrolyse it producing hydrogen for the power plant/drives and oxygen for life support, excess vented into space.

No one (in this thread, anyway) has suggested that you can use hydrogen directly from water to jump drive. What we're talking about is a second load of hydrogen, carried along as water and split into hydrogen and oxygen to fill the fuel tanks for the jump drive again after they've been emptied.


Hans

 

[HG_B]

That's a meta-reason. That has zero to do with the in-game reality. The in-game reality (until and unless retconned) has people carrying around spare fuel in the form of liquid hydrogen rather than water. That's a stone cold in-game fact.

So, do tell. What happens if you carry 1 Dton of water in the cargo bay and feed it into your fuel purif plant. How many Dtons of LHyd do you get?

You get ~1.6 Dtons of LHyd. THAT, is the "in game reality". That's a stone cold, in-game fact.

 

[rancke]

So, do tell. What happens if you carry 1 Dton of water in the cargo bay and feed it into your fuel purif plant. How many Dtons of LHyd do you get?

You get ~1.6 Dtons of LHyd. THAT, is the "in game reality". That's a stone cold, in-game fact.

So? Perhaps you should re-read my original comment. I specifically stated that there doesn't seem to be any reason why it wouldn't work (But see Wil's post above). Yet evidently there is a reason, since people evidently don't do it.


Hans