CT Only: Skimming

[sabredog]

I checked the pages in AHL Book 1 to see what the deal was with frontier refueling something like that and got different info from TCS and other (albeit skimpy) sources.

The AHL has 35,000 tons of fuel. The four fuel shuttles can skim and process (with their onboard refineries as they fly to and from the AHL) 350 tons each in 3 hours. If all four skim at once they can tank up the AHL in 27 four-shuttle trips, or 3 days total.

Refueling using free water from a world takes twice as long (6 hours per load). Using ice takes 9-10 hours per shuttle load.



The AHL can skim herself, but it is risky given her size. The rules don't say how long it takes, other than the ship just dives in, opens her scoops, and slurps it up. It is pretty dramatic, though.

The ship, due to size and design, and be damaged or even lost doing this.
The ship can have fuel tanks collapse from hull stress and buckling. The Maneuver Drives can be buffeted and damaged to even the point of failure - which then results in the loss of the entire ship.

All this sounds weird considering how routine all the rest of the Traveller rules, editions, and games that mention it make it sound. It is discussed as routine procedure when fleets Jump into a system, and the AHL is the only ship in the lists that I've ever seen that mentions having to use fuel shuttles to do this safely. How bad would it be to skim a Tigress and lose the thing because the drive get knocked around?

 

[sabredog]

Not quite, the rules are a little fuzzy on if you need all three drives. You definitely need a power plant for your maneuver drive, but it doesn't explicitly state like it does in future editions that you need a power plant at least equal to the jump drive - this is how the x-boat began.

Also, the '77 edition (the one I have right here) specifically states the power plant is for internal power and the maneuver drives, and that it has to be the same size as the M-drive, accordingly. There isn't anything fuzzy about it.

In the Fighting Ships supplement it says the X_boats don't have a power plant. Only a jump drive.


It changed, like you said with the '81 edition.
I remember I had to do a lot of remodeling lists of ships when the '81 edition came out to fix that. Same with HG2 for different reasons.

 

[whartung]

I checked the pages in AHL Book 1 to see what the deal was with frontier refueling something like that and got different info from TCS and other (albeit skimpy) sources.

The AHL has 35,000 tons of fuel. The four fuel shuttles can skim and process (with their onboard refineries as they fly to and from the AHL) 350 tons each in 3 hours. If all four skim at once they can tank up the AHL in 27 four-shuttle trips, or 3 days total.

Refueling using free water from a world takes twice as long (6 hours per load). Using ice takes 9-10 hours per shuttle load.

The AHL can skim herself, but it is risky given her size. The rules don't say how long it takes, other than the ship just dives in, opens her scoops, and slurps it up. It is pretty dramatic, though.

Right, the question is does the shuttle take 3 hours because it's 350 tons? Or just because it's a shuttle? i.e. if it was a 1000 ton fuel shuttle, would it also take 3 hours? Do the scoops scale with the ship? Does the AHL ship fuel up in 3 hours if extra excitement?

It's not a bad baseline ruling. You could make the ship refuel time be something like the cube root of the fuel volume in hours. 10,000 tons in 100 hours. Seems kind of high.

Mind, the 3 hours for the fuel shuttle includes travel, skimming, travel, and transfer.

 

[ffilz]

One thing of note is that the 1977 rules don't mention WHAT star ship fuel is, just that it can be skimmed from gas giants (unrefined) or purchases (refined and unrefined) from star ports.

I'm inclined to take that at its word. Sure, I'm using deck plans based on 1 dTon is the volume of 1 ton of liquid hydrogen, but that doesn't mean the fuel has to strictly be liquid hydrogen.

Doing this I don't have to allow water or ice as fuel sources...

Since I run a Books 1-3 campaign, I don't have to worry about fuel purifiers (and note that per the 1977 rules, a military ship isn't totally immune to issues of unrefined fuel, so it doesn't necessarily have fuel purification, it just can more safely use unrefined fuel).

Frank

 

[AndyW]

I've thought a bit about GG skimming over the years. It seems to me that the typical GG is a high G environment, often with winds that would shame a typical F11 tornado. Skimming must be a little like skipping a stone across a pond, too steep an entry and you dive deep and are lost, too shallow and you bounce off quickly, losing the efficient collection of Hydrogen. Come in too hot and you incinerate, come in too slow and you lose the momentum needed to get out unless you are running drives that top the gravitational acceleration. A great deal of handwavium is needed to justify the process on many fronts.

It occurs to me that a 1 G ship is playing Russian roulette to dive into a GG atmo at all. That said, I had a little take away from the Starship Operators Manual. It mentions overdriving an M-drive for the purpose of off axis thrusting, and that a competent engineer could do this to multiples of the drives rating for short periods. So I got to thinking that in addition to involving a pilot in the skill roles to successfully perform the maneuver, the engineer would play a crucial role in giving the necessary juice to get out.

Taking it further I conceived of a maneuver that dumps the high speed skimming process for something I call the "dunk and guzzle". Which is rather like submerging an empty glass, mouth up in a pool of water until the water starts pouring in.

The pilot/navigator chooses a relatively calm yet dense pocket of the GGs atmo, orients the vessel stern down and drops as low as safely practical in the atmo, opens the scoops and collects gas. The engineer strokes and coos and baby talks the M-drives all the while, thrusting at an appropriate multiple of its typical thrust. Enough to maintain the right depth. EMS and densitometers would provide "weather forecast" for the purpose of orienting the vessel's streamlining to minimize buffeting.

Hull stress and heating would be minimized and it would be easier to concentrate on regions and/or strata that are richer in hydrogen.

This is a process that I would include IMTU.

 

[Fovean]

Very cool idea.

It would be quite a spectacle, sinking slowly into the mists with the occasional electrical or radiation storm on the horizon.

I would probably rule it takes an extra 2D hours or some such, to make the more difficult but faster “hot skim” (the skipping stone maneuver) a necessary option when under a time crunch during an adventure. But then the dunk n guzzle could lead to a cool submarine hunt scenario, all sweaty, tense sensor rolls with an occasional burst of fire... I wonder how missiles do in a GG atmosphere?

 

[pavel.k]

It sounds nice - slow sinking to the sun. But would the ship be able to escape? The Sun has gravity 27.9 G and escape velocity is 617.5 km/s.

 

[estar]

Nope. orbital mechanics doesn't work like that, especially when you have a magical maneuver drive that can provide a minimum of 1g continuous thrust for a month or more.
it's much easier just to find a lump of ice (water/methane/ammonia) to extract hydrogen from.

The problem is time whether a thrust of 9.8 m/sec^2 add enough delta-vee fast enough to overcome the loss from flying through an atmosphere. There will be a depth at which you lose so much per second that your maneuver drive can't counteract it.

The higher the thrust rating the deeper that depth is.

I created Traveller ships in Orbiter Space simulator and see what it took to fly them including flying through the atmosphere of a gas giant. The issue mostly cropped up with 1-G and 2-G maneuver drives.

 

[AndyW]

It sounds nice - slow sinking to the sun. But would the ship be able to escape? The Sun has gravity 27.9 G and escape velocity is 617.5 km/s.

You couldn't do that, but a 2-3G Gas Giant wouldn't pose too much of a problem if one is talking a few hundred degrees vs. several million.

 

[AndyW]

. I wonder how missiles do in a GG atmosphere?

I would think that they would end up acting a lot like depth charges. They would have issues achieving a direct impact, due to cross winds, but could be set to go off when a proximity detonator detected a metallic substance nearby. That would take your sub hunt scenario up a few notches.

 

[Kakistocrat]

As I see it, MM and company didn't consider the difference between compressed gas and liquified hydrogen, nor the size of equipment needed, nor the complications as described.

Nor the need for an oxidizer, e.g. liquid oxygen, to utilize liquid hydrogen as a fuel. (I think that a typical consumption ratio of liquid oxygen to liquid hydrogen is six to one.)

 

[Kakistocrat]

One thing of note is that the 1977 rules don't mention WHAT star ship fuel is, just that it can be skimmed from gas giants (unrefined) or purchases (refined and unrefined) from star ports.

That’s true, but given that the knowledge of gas giant atmospheres in 1977 was limited to those of Jupiter, Saturn, Uranus, and Neptune, and that all of their atmospheres are overwhelmingly composed of hydrogen, it’s reasonable to conclude that skimming for hydrogen (with onboard liquefaction of the skimmed gas) was the intention.

Doing this I don't have to allow water or ice as fuel sources...

If you’re not allowing hydrogen as a fuel to prevent water and ice from being fuel sources, may I ask which elements would be sought after as fuel from skimming gas giant atmospheres?

 

[whartung]

Nor the need for an oxidizer, e.g. liquid oxygen, to utilize liquid hydrogen as a fuel. (I think that a typical consumption ratio of liquid oxygen to liquid hydrogen is six to one.)

The hydrogen does not need oxygen for fuel, it's not "burned". It's not "oxidized". It's fusion. It's nuclear, not chemistry.

With TNE, the Hydrogen is used as reaction mass as well, but is still not "burned", it's "simply" heated to plasma.

 

[ffilz]

That’s true, but given that the knowledge of gas giant atmospheres in 1977 was limited to those of Jupiter, Saturn, Uranus, and Neptune, and that all of their atmospheres are overwhelmingly composed of hydrogen, it’s reasonable to conclude that skimming for hydrogen (with onboard liquefaction of the skimmed gas) was the intention.

If you’re not allowing hydrogen as a fuel to prevent water and ice from being fuel sources, may I ask which elements would be sought after as fuel from skimming gas giant atmospheres?

For my game, I don't care. Jump drive is all pseudo science mumbo jumbo. The mumbo jumbo of Classic Traveller Books 1-3 (especially 1977) is that fuel is acquired by skimming gas giants or buying it at a star port. Exactly what the fuel is doesn't matter to me. Going down the route of locking in what some aspect of SF technology actually is can lean to extrapolations that totally break the existing rules. I've played that game before. Today I want to play the rules in those three little books.

 

[Kakistocrat]

The hydrogen does not need oxygen for fuel, it's not "burned". It's not "oxidized". It's fusion. It's nuclear, not chemistry.

OK. Given a fusion power plant, then perhaps refined fuel is pure deuterium (hydrogen-2), and unrefined fuel is a mix of deuterium and tritium (hydrogen-3) — far more energy-rich than pure deuterium when it’s a 50-50 blend, but requiring extra care when undergoing annual maintenance, e.g. dealing with tritium’s radioactivity.

 

[Kakistocrat]

For my game, I don't care. Jump drive is all pseudo science mumbo jumbo. The mumbo jumbo of Classic Traveller Books 1-3 (especially 1977) is that fuel is acquired by skimming gas giants or buying it at a star port. Exactly what the fuel is doesn't matter to me. Going down the route of locking in what some aspect of SF technology actually is can lean to extrapolations that totally break the existing rules. I've played that game before. Today I want to play the rules in those three little books.

You can certainly run your game as you see fit. “Can lean to extrapolations that totally break the existing rules” is of course not the same as “must lean to extrapolations that totally break the existing rules”; for example, given a fusion power plant, the unrefined fuel skimmed from gas giants could be helium-3, which is much more common in gas giant atmospheres than in Earth’s atmosphere.

 

[mike wightman]

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'.

 

[Kakistocrat]

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.

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). The hydrogen in ocean water is on the order of 99.98% protium, 0.02% deuterium. I wouldn’t rule out other sources of hydrogen to get the fuel isotopes, but I don’t know if those isotopes have a similar distribution in ammonia or methane.

In the case of our solar system, going to Pluto to skim methane could come at the cost of additional interplanetary travel time — something on the order of 18.7 days for a one-way trip from Earth (presuming that Earth is on the same side of Sol as Pluto, using a distance halfway between Pluto’s aphelion and perihelion, with constant 1 G acceleration/deceleration). A similar one-way trip to Jupiter to skim hydrogen would be around 6.8 days.

The stipulation that it is hydrogen led 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'.

I agree with your view of shipboard fuel purification plants in LBB5. I see a filtering mechanism as part of skimming (e.g. to ensure that no fish are taken onboard with ocean water), but not a refining capability. Regarding the setting mystery, it could be that starport owners do not want to take a chance with onsite purification plants having a catastrophic industrial accident which could destroy the starport.

 

[ffilz]

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.

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.

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

 

[whartung]

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). The hydrogen in ocean water is on the order of 99.98% protium, 0.02% deuterium. I wouldn’t rule out other sources of hydrogen to get the fuel isotopes, but I don’t know if those isotopes have a similar distribution in ammonia or methane.

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.

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. 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.

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.

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 it 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.

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.