CT Only: Skimming

[mike wightman]

Turning ice into liquid water shouldn't take much doing - just turn off the magic heat sinks and the waste heat from your gigawatt fusion reactor will do the trick in no time...

by the way I don't think dipping for fuel is mentioned in 77 CT - I will have to check.

 

[Kakistocrat]

See, all this discussion of implications of various choices.

Leave it unspecified and you can skim a gas giant for unrefined fuel and then it makes sense that only a Star Port E would not at least have unrefined fuel available since any other star port has in-system craft to go skim the gas giants.

Whether it is unspecified or specified, if a gas giant can be skimmed for unrefined fuel, then that unrefined fuel must be something that is both suitable (if not necessarily ideal) for fusion power plants and available in the atmospheres of gas giants. That something is not necessarily exclusively found in the atmospheres of gas giants; the time it takes for in-system craft to make round-trip skimming runs to the nearest suitable gas giant might make such harvesting less economically viable than e.g. having a planetside factory extracting unrefined fuel from the system’s main world, and using tanker shuttles between the factory and the starport.

Now systems that don't have a gas giant? Well, maybe there's a way to get fuel from other planet types but it isn't practical for a ship to do and can only be done by a star port. And, while some star ports (C and D) can get that source, they don't have the resources to go one step farther and refine it.

It could be impractical, or it could be practical; that depends on what the unrefined fuel is and whether that can be extracted from the system’s other planets. Note that starports A and B have refined fuel available ; that doesn’t necessarily mean that unrefined fuel is refined onsite at those starports.

What is it? How is it extracted without a gas giant? How is it refined? I dunno. I play the game Traveller...

Figuring out what it is, how it would be extracted without a gas giant, and how it would be refined does not mean that one is no longer playing Traveller.

 

[Kakistocrat]

Well, canonically, "gases skimmed from Gas Giants", water, and ice are all viable raw materials for Starships. Gas Giant skimming and water dipping are iconic starship actions for fuel.

It's hard enough for a ship to get the fuel it needs in a timely matter as is, without throwing away 99.98% of it as waste.

I agree with those being iconic starship actions. Getting the fuel in a timely matter is unrelated to discarding unsuitable skimmed isotopes — since the erratum for 1981 Book 3 states that the actual skimming procedure requires eight hours, far more relevant to timeliness is the distance travelled to the unrefined fuel source.

Starship Fuel is either Refined or Unrefined, but it's never been made clear how to get from Gas Giant Skimmings or Water to Unrefined, or Refined fuel.

All too true — hence this thread.

We know there are refinement plants for ships, we do not know their efficiency. How man dTons of Skimmings does it take to get a dTon of Refined fuel, and why is ANY fuel "Unrefined", anywhere?

We only know it's an efficient process as ships seem to routinely do it, especially for wilderness refueling. It's also premised by the concept of first class fuel skimmers used to fuel larger ships that are unable to skim Gas Giants or dip water directly.

With Book 5, there are shipboard purification plants, but not everyone uses Book 5. Given Book 5’s “[Equipment malfunctions and misjumps] can be avoided with the use of a fuel purification plant which allows refining of the raw gas before it is used in the drives”, and the lack of a requirement for a separate tank for unpurified raw gas, I’d see the purification plant as working as fast as the raw gas can be skimmed, with the purification plant being an intermediate step between raw gas in the fuel scoops and refined fuel in the fuel tank. Without knowing what the impurities are in unrefined fuel, the conversion ratio of a volume of unpurified raw gas to a volume of purified refined fuel will vary by Traveller universe. Unrefined fuel exists because the books state that it exists.

The primary inefficiency from a trade perspective of Gas Giant skimming is simply locale. Gas Giants tend to not be the hub of commerce but days, or weeks away at normal space speeds.

I agree.

Why ships would not routinely dip ocean water instead of paying for fuel by the ton at the Starport is not clear (could simply be legislative — illegal to dip water from our oceans), but what is clear is that Starports sell fuel and ships deign to purchase it, which suggests it's "better" for perhaps some intangible reason to buy Starport fuel over wilderness dipping.

Yes, planetary law could limit or forbid ocean skimming. The likeliest intangible reason is the time/money tradeoff; is it worth CR 500⁄ton (or CR 100⁄ton with a purification plant) to not spend a couple of weeks lawfully skimming the closest raw gas source?

I can't imagine in any but the most desperate reason why a starship would use ice as fuel if a Gas Giant or liquid water was available. Ice would be a last resort, what a lot of work and power to get enough ice melted and loaded. But, when you're several parsecs from anywhere, you do what you have to do.

Perhaps some shipyards offer bespoke “icebreaker” hulls for interested customers.

 

[Condottiere]

No one is going to let you dip your hose into their ocean, for free; also, environmental concerns and waste disposal.

Anyone who's thought about, knows that gas giant skimming is only when other options are less palatable, because detouring to do it wastes time, and puts your starship at unnecessary risk, strains your components, and may not be covered under your insurance policy.

 

[ffilz]

Whether it is unspecified or specified, if a gas giant can be skimmed for unrefined fuel, then that unrefined fuel must be something that is both suitable (if not necessarily ideal) for fusion power plants and available in the atmospheres of gas giants. That something is not necessarily exclusively found in the atmospheres of gas giants; the time it takes for in-system craft to make round-trip skimming runs to the nearest suitable gas giant might make such harvesting less economically viable than e.g. having a planetside factory extracting unrefined fuel from the system’s main world, and using tanker shuttles between the factory and the starport.

Sure, I'm ok with a factory being able to extract fuel planetside and leave gas giant skimming as something desperate PCs and military ships do.

It could be impractical, or it could be practical; that depends on what the unrefined fuel is and whether that can be extracted from the system’s other planets. Note that starports A and B have refined fuel available ; that doesn’t necessarily mean that unrefined fuel is refined onsite at those starports.

Yea, that's possible, but who would ship refined fuel that sells at 500 cr per ton when you can get 1000 cr per ton carrying cargo? And even worse is unrefined fuel at 100 cr per ton (which if not available locally would also have to be shipped).

Figuring out what it is, how it would be extracted without a gas giant, and how it would be refined does not mean that one is no longer playing Traveller.

True, but if figuring it out leads to a logic path that allows different choices of how to get fuel from what is stated in the rules, then one is changing the rules. And my feeling is that these kinds of extrapolation exercises start a chain of reasoning that winds up growing and hitting more and more of the game system until there is nothing left. So I choose to not do the extrapolation any more than maybe is necessary (sometimes you need to spew some technobabble to keep the game narative making sense) so that I don't get tempted. Because before I started running Classic Traveller, I WAS doing extrapolation exercises and talking myself out of a game with interstellar trade and travel and colonies struggling on less than ideal worlds.

 

[Kakistocrat]

Yea, that's possible, but who would ship refined fuel that sells at 500 cr per ton when you can get 1000 cr per ton carrying cargo? And even worse is unrefined fuel at 100 cr per ton (which if not available locally would also have to be shipped).

It’s commercial starships that get CR 1,000 per ton of delivered cargo. Commercial non-starships don’t necessarily get that rate, e.g. CR 10 per ton of delivered cargo by shuttle (1977 Book 2, page 8).

True, but if figuring it out leads to a logic path that allows different choices of how to get fuel from what is stated in the rules, then one is changing the rules. And my feeling is that these kinds of extrapolation exercises start a chain of reasoning that winds up growing and hitting more and more of the game system until there is nothing left. So I choose to not do the extrapolation any more than maybe is necessary (sometimes you need to spew some technobabble to keep the game narative making sense) so that I don't get tempted. Because before I started running Classic Traveller, I WAS doing extrapolation exercises and talking myself out of a game with interstellar trade and travel and colonies struggling on less than ideal worlds.

This is why I’m interested in finding a logic path that is as compatible as possible with the rules and with practical knowledge (e.g. science, economics). The rules state that unrefined starship power plant fuel can be sourced from gas giants (1977 Book 2, page 4), and given the existence of refined fuel, it is axiomatic that unrefined fuel can somehow be refined. 1980 Book 5 explicitly states that the fuel is hydrogen (page 17). Given these rules in tandem with the science of hydrogen fusion and the rules for starship economics, how are these best melded into a coherent background for a Traveller setting? Perhaps I enjoy this extrapolation process more than others do. A tolerance for extrapolation can certainly vary from one person to another — for example, I’m perfectly content to not allow Book 5 shipboard fuel purification systems — but I think that few people would be so determined as to extrapolate the entire game system out of existence.

 

[kilemall]

One simplifier- think of refined fuel as less a 'profit center' and more a loss leader for the general support of interstellar trade.


The starport subsidizes the refining of fuel and uses an interstellar standard of cost to help defray but not eliminate the overhead of providing the service.


When you consider the time loss cost not to mention risk of skimming/refining plus the tonnage tied up in the refiner that could be profitable tonnage/staterooms, most ship designers and commercial operators will opt for the starport refuel, as long as it's 'standard cost'.

 

[Kakistocrat]

One simplifier — think of refined fuel as less a 'profit center' and more a loss leader for the general support of interstellar trade.

The starport subsidizes the refining of fuel and uses an interstellar standard of cost to help defray but not eliminate the overhead of providing the service.

Given the considerable difference in “retail” price between refined fuel and unrefined fuel, I’d considered that difference to be mainly comprised of an excise tax that is eventually remitted to the Imperium (in its generic Book 5 “remote centralized government” sense) to help fund its interstellar responsibilities. I imagine starship fuel refineries as being independent of (and located away from) starports, just as aviation fuel refineries are independent of (and located away from) airports; and that starship fuel refineries are capital-intensive to construct, but that the fuel refining process itself at a refinery is relatively inexpensive on a per-ton basis. For systems with starports but without any in-system source of unrefined fuel, perhaps Imperial subsidization of importing fuel to those systems are what allow those starports to sell fuel at all.

When you consider the time loss cost, not to mention risk of skimming/refining plus the tonnage tied up in the refiner that could be profitable tonnage/staterooms, most ship designers and commercial operators will opt for the starport refuel, as long as it's 'standard cost'.

Presuming that “time is money” also applies within a Traveller setting, I agree that most would opt for filling up at starports.

 

[Straybow]

By stipulating hydrogen is the fuel you open up the :CoW:

Water, liquid ammonia and liquid methane are all more compact sources for hydrogen.

Water, ammonia and methane are pretty common throughout a system - why bother with a gas giant when you can get your unrefined fuel from Pluto.

The stipulation that it is hydrogen lead to the purification plant in LBB5 which is a truly setting breaking invention - why any starport of any type doesn't have a purification plant on hand is a setting mystery. Why enterprising PCs wouldn't buy purification plants and operate them under licence at lesser starports and rake in money hand over fist is also unexplainable without referee fiat telling the players they can't due to 'reasons'.

As I mentioned above, fuel purification is an automatic feature of liquifaction. Everything except helium will precipitate out before the hydrogen liquifies. Then the helium gas can be bled off from the liquifying hydrogen. Voila, purified.


So what breaks the setting is the distinction between purified and unpurified.

 

[Straybow]

That’s why I’d see the hydrogen isotopes deuterium and tritium as being fuel sources for a fusion plant, but not the standard hydrogen isotope protium (hydrogen-1).

Years ago I calculated that the amount of energy derived from a ton of LH2 corresponds to the fusion of about 50% the natural 0.015% D within it and conversion to power at about 50% efficiency. The actual acceleration equation would be different, P=k·a²·m, but since we don't know k you end up at the same guesswork solution.

Deuterium

 

[aramis]

As I mentioned above, fuel purification is an automatic feature of liquifaction. Everything except helium will precipitate out before the hydrogen liquifies. Then the helium gas can be bled off from the liquifying hydrogen. Voila, purified.


So what breaks the setting is the distinction between purified and unpurified.

The ²He and the ²H (aka ²D) are going to be different from the ¹H... and each other.

Hydrogen	Deuterium	Helium ²He
Formula H2 Molecular Weight (lb/mol) 2.02 Critical Temp. (°F) -400.0 Critical Pressure (psia) 187.5 Boiling Point (°F) -423.0 Melting Point (°F) -434.5 Psat @ 70°F (psia) (note 1) Liquid Density @ 70°F (lb/ft3) (note 1) Gas Density @ 70°F 1 atm (lb/ft3) 0.0052 Specific Volume @ 70°F 1 atm (ft3/lb) 191.90 Specific Gravity 0.069 Specific Heat @ 70°F (Btu/lbmol-°F) 6.87	Formula D2 Molecular Weight (lb/mol) 4.03 Critical Temp. (°F) -390.8 Critical Pressure (psia) 241.5 Boiling Point (°F) -417.0 Melting Point (°F) -426.0 Psat @ 70°F (psia) (note 1) Liquid Density @ 70°F (lb/ft3) (note 1) Gas Density @ 70°F 1 atm (lb/ft3) 0.0104 Specific Volume @ 70°F 1 atm (ft3/lb) 95.97 Specific Gravity 0.142 Specific Heat @ 70°F (Btu/lbmol-°F) 6.95	Formula He Molecular Weight (lb/mol) 4.00 Critical Temp. (°F) -450.3 Critical Pressure (psia) 33.0 Boiling Point (°F) -452.1 Melting Point (°F) -- Psat @ 70°F (psia) (note 1) Liquid Density @ 70°F (lb/ft3) (note 1) Gas Density @ 70°F 1 atm (lb/ft3) 0.0103 Specific Volume @ 70°F 1 atm (ft3/lb) 96.65
www.AirProducts.com Hydrogen	www.AirProducts.com Deuterium	www.AirProducts.com Helium

Note that the Deuterium, which we need most, is the first to liquify, then the hydrogen, then finally the helium... but practical cooling is the problem.

 

[kilemall]

Hmm while we are on the topic of specific fuel composition, thought I would mention that my CT/HG hybrid has an expanded radiation hit effect table, which includes fuel hits. Rad hits don't destroy the fuel, but they contaminate it to be unrefined, which means either reprocessing the irradiated fuel or reskimming.



Fuel purifiers are potential hits too, so a ship could end up with no ability to jump safely and have to risk it, or get refined fuel pumped over from another ship.


That might make Battle Riders that much more attractive since only hits on the carrier count for jump capability.

 

[mike wightman]

I found this interesting tidbit while perusing LBB5 79 to see if it sheds any light on another matter:

Fuel used for ships is light elemental gases, especially hydrogen.

page 17
this is changed to:

Fuel used for ships is hydrogen

in HG 80.

So, pre-HG80 the fuel skimmed from a gas giant could be hydrogen, helium, possibly neon and argon could qualify as a light elemental gasses.

 

[whulorigan]

I found this interesting tidbit while perusing LBB5 79 to see if it sheds any light on another matter:
page 17.

[FONT=arial,helvetica]

Fuel used for ships is light elemental gases, especially hydrogen.

[/FONT] So, pre-HG80 the fuel skimmed from a gas giant could be hydrogen, helium, possibly neon and argon could qualify as a light elemental gasses.

Or possibly Nitrogen and Oxygen, which are reasonably common in both diatomic state as well as in "ices". (Fluorine might fit, but is somewhat rarer).

 

[mike wightman]

Depends on the definition of light I suppose.
H2 - 2
He - 4
Ne - 20
Ar - 40
N2 - 28
O2 - 32
F2 - 38

 

[Straybow]

⁴He. I'm pretty sure ²He doesn't exist, except for a few nanoseconds.

 

[mike wightman]

Less than a nanosecond apparently.

 

[Grav_Moped]

...
Note that the Deuterium, which we need most, is the first to liquify, then the hydrogen, then finally the helium... but practical cooling is the problem.

Look --- somehow in the Traveller universe, they can keep multi-megawatt fusion reactors from slagging themselves without needing enormous radiators. Chilling a little bit of hydrogen isn't going to be an issue.

 

[BRover]

Look --- somehow in the Traveller universe, they can keep multi-megawatt fusion reactors from slagging themselves without needing enormous radiators. Chilling a little bit of hydrogen isn't going to be an issue.

True--which may explain the size and cost of drives. I mean, you need plenty of space for all that handwavium's standing waves--and it doesn't come cheap . . .

 

[BackworldTraveller]

Look --- somehow in the Traveller universe, they can keep multi-megawatt fusion reactors from slagging themselves without needing enormous radiators. Chilling a little bit of hydrogen isn't going to be an issue.

Chilling the hydrogen isn't the problem - having it change state once chilled can be. As the liquid changes state it can release enough energy to vaporise some of the remainder...Pop!