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Old December 23rd, 2018, 04:41 PM
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Default Skimming

I'm curious about the process of skimming fuel at a gas giant. I know the ship must be fitted with fuel scoops and a fuel purifier, and basically, the ship is piloted deep into the atmosphere, with the scoops open, scooping in hydrogen.

How long does it take? I think I recall some scoop times in one of the supplements or adventures (maybe Trillion Credit Squadron? Or maybe Leviathan?).

In 1981 CT, it seems that fuel purifiers are part of the Jump Drive, right? They had to be purchased separately in the first version of High Guard--I think.



I guess it's not a too dangerous process since I don't recall seeing any CT rolls (I remember MT's SOM has a roll) to complete the skimming.

I'm guessing the ride can be like an airplane going through a bad storm, with lightning and a bumpy ride. Or, it can be smooth.

How about processing time for the fuel? How long before the ship can jump? How much time does a ship that is skimming fuel from a GG hang around the GG?

Oh, and diving too deep into the atmosphere of the GG must pose a problem for some ships in that, at a point, the ship cannot again attain escape velocity.




What are your thoughts on this?



EDIT: This could be one of those tasks that requires no roll but does require skill. Say, Pilot-1 required to skim.
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Old December 23rd, 2018, 05:07 PM
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Originally Posted by Supplement Four View Post
I'm curious about the process of skimming fuel at a gas giant. I know the ship must be fitted with fuel scoops and a fuel purifier, and basically, the ship is piloted deep into the atmosphere, with the scoops open, scooping in hydrogen.
You need fuel scoops fitted to scoop the fuel. Fuel purification plants are an option from High Guard, under LBB2 military drives can use unrefined fuel.

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How long does it take? I think I recall some scoop times in one of the supplements or adventures (maybe Trillion Credit Squadron? Or maybe Leviathan?).
It is mentioned in a couple of places, I will check and edit.

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In 1981 CT, it seems that fuel purifiers are part of the Jump Drive, right? They had to be purchased separately in the first version of High Guard--I think.
Nope.

Fuel purification plants are only an option in High Guard, both editions. LBB2 77/81 and TTB/SE have not purification plants just the note that military drives can use unrefined fuel. There are no civilian fuel purification plants under LBB2 rules.

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I guess it's not a too dangerous process since I don't recall seeing any CT rolls (I remember MT's SOM has a roll) to complete the skimming.

I'm guessing the ride can be like an airplane going through a bad storm, with lightning and a bumpy ride. Or, it can be smooth.
Unless something completely out of the blue happens you are basically just falling through the atmosphere a few times until your tanks are full.

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How about processing time for the fuel? How long before the ship can jump? How much time does a ship that is skimming fuel from a GG hang around the GG?
Purification rates are given in HG and Trillion Credit Squadron.

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Oh, and diving too deep into the atmosphere of the GG must pose a problem for some ships in that, at a point, the ship cannot again attain escape velocity.
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.
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What are your thoughts on this?
it's much easier just to find a lump of ice (water/methane/ammonia) to extract hydrogen from.
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EDIT: This could be one of those tasks that requires no roll but does require skill. Say, Pilot-1 required to skim.
The autopilot is probably up to the task.
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Old December 23rd, 2018, 06:14 PM
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Scoop times are in the Azhanti High Lightning rules in the sections about the fuel shuttles and refueling the ship. It takes quite a while to just get the raw gas to the ship and fill up, plus the time for processing. It can be speeded up by using the ship's scoops but as pointed out in the sourcebook maneuvering t a ship that size and larger inside a jovian atmosphere is tricky sometimes and the ship can be badly damaged.


Skimming would require going deeply enough to find a dense enough atmosphere to make it worthwhile, or at least reduce the time require to tank up to a reasonable level. It would also require having enough of the right gases under the right atmospheric conditions to even bother with. Especially with a fleet doing it. You can see why the first priority of any fleet Jumping in-system is to secure the gas giant(s) and tank up ASAP once you have the pickets out.

As Mike pointed out you won't get trapped in the skim unless you lose maneuvering power at 1G+, but you could hit a gasberg. Scoop a greeblie in the intakes and clog them. Scoop one into a tank even, though I assume "bug-screens" are up and functioning to keep the greeblies out. And in a ship the size of the AHL it wouldn't make any difference, of bypass vents could deflect solids out of the intake stream.

But that's how it has been IMTU and others' will vary.

I require a regular 8+ base throw for the pilot to perform the skim, modifiers of skill are added. Failure just adds time to the skim or reduces how much gas you can pull out of the skim. Maybe the pilot should take her deeper for a better density? 9+ gets your skim time reduced by a quarter. 10+ another quarter....and so on. Failure beyond the first layer means you might hit a gasberg, or get hit with massive electrical discharges that detonate pockets of volatile gases covering an area the size of Texas....and so on.

Players have been stuck on gasbergs and had to figure out how to get the ship unstuck without making it all worse in various ways. It depends on the gases involved but you'd have a little mini moon of frozen gas layers that might crumble, sublime off to get into crevices and cracks as the gasses react to the warmth of the ship, thus getting it stuck worse - or being covered with frozen gases that crept around on the ship.

Flying and floating greeblies might attack players that are outside trying to free the ship....if a floating greeblie was hit by a round that detonated its massive gas bag filled with hydrogen then there can be a chain explosion that would be a lot of fun. In any case, players have always enjoyed the atmosphere of such things.
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Old December 23rd, 2018, 08:25 PM
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Fuel scooping wouldn't work. A ship doesn't have the equipment to liquify the fuel. Actually, 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.

Of course, it takes 14 GJ/ton to liquify H2 if you installed a plant on the ship. It looks like a turbine engine, except in reverse. A ship might have a tiny one, just to reliquify boil-off. Since the hydrogen has to be cooled to about 20 K the purifier absolutely cannot be in the engineering section, which would get really hot while operational.

Next problem is compression. Scooping would use kinetic energy to compress the gas, but to what limit? You might be able to squeeze ton of non-cryogenic H2 gas into a 1 ton LH2 tank. This tank has to be specially built for pressurized storage since normal LH2 tanks are unpressurized. Pipes, valves, and pumps are different for H2 vs LH2 as well. So, you process the gas from the capture tank into your fuel storage tanks.

If your high pressure tank is half of your total fuel tankage, then it would take four passes to fill the remaining half with LH2. Now where do you put the LH2 after processing the next load of captured H2? You need temporary tankage. It can't be external, since you wouldn't be able to do a hypersonic pass through the atmosphere with external collapsible tanks. So you need an internal collapsible tank for holding processed LH2 until after the last pass. So now how small is the collapsed holding tank with an expanded capacity equal to half your fuel tankage? Does it collapse to maybe of the full size? Take that out of your precious cargo space. And be sure to have enough empty cargo space for the other of the holding capacity.

It would actually be slow, repetitive, and space-consuming to have scooping capability on a starship.
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Old December 23rd, 2018, 08:27 PM
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Fuel scooping wouldn't work. A ship doesn't have the equipment to liquify the fuel.
So, you are disagreeing with what has been established in Traveller in the way of scoops and fuel skimming?
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Old December 23rd, 2018, 08:32 PM
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Yes. 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.


Just sayin'.
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Old December 23rd, 2018, 08:42 PM
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It's goofy, to be sure. As I said, you'd have to go deep to even get the density realistically needed to scoop anything worth the trouble.

Buuuut...Traveller ships has frontier refueling capability and refinery equipment built in with scoops n' all. And giant talking starfish. And uplifted pirate dogs.*

So frontier refueling works for me.


* and I have gasbag greeblies and tentacled swoopers living in the Jovian biome that have been transported (eggs and juveniles) to almost all the GG's used regularly by ships. Scifi invasive species. At least the ones that make it past bug-screens (damaged screens or if the pilot forgot to deploy them before the skim). I ain't giving that stuff up for realism's sake.
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Old December 23rd, 2018, 09:10 PM
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I don't think you need to dive deep at all. A scramjet can operate above 20km, which is about 50 millibars. Scooping would probably be effective down to 1 millibar, but might be optimized at 5-10 millibar. That would be about 150-200 km above the cloud level on Jupiter.


If you go into denser atmosphere you will sacrifice too much momentum for no purpose. You want to minimize the operational time spent on scooping, which means conserving momentum. You want to dip down and bounce back off the atmosphere with just enough dwell time to capture and compress the gas.
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Old December 23rd, 2018, 10:47 PM
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But if it isn't practical at all, or realistic, then what difference does it make?

Actually, though, the atmosphere would be denser the deeper into it you go, sure it would take more energy to go there but we are not talking about having to worry about if you have enough Delta-V to come back up with ordinary reaction engines or if you let too much energy bleed off the drives won't have enough power....etc..

We are working with directionless magic drives that are anti-grav and not affected by inertia. Even with the rules in the game for laying out vectors and gravity maneuvers there is more than sufficient D-V for anything with a 1G drive to make it back out again just fine. An air/raft could make it out again given the rules.

Better to worry more if the gas giant in the system is even capable of refueling ship or fleet. If not, then does the world have enough free water or ice?

Now I also freely acknowledge the absurdity of it all, but since it is in a game I accept it as realistic within that game's reality.
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Old December 24th, 2018, 03:19 AM
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Don't forget that gas giants have serious gravity, so your ship needs to make a run at the planet to have enough delta vee to zip through even if you have M-drive failure.

Interesting point I had not seen before on reviewing LBB5- small craft do not require fuel purification. That would seem to be in line with the CT rules on unrefined fuel risking misjumps.

TCS as I recall had the bit about speed of refueling in terms of a week under different fuel scenarios and total fuel available at X starport level. But I seem to also recall there was some calculation for amount of time and passes involved, which defined the amount of time the fleet was at risk and required the High Guard protecting fleet.

And that there was a tradeoff between having a streamlined/semi-streamlined fleet that could go through and fuel itself vs. a small craft/specialized tanker setup.
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