Gas giant refuelling

[phavoc]

The Juno mission to Jupiter is giving us new information we never had before. This article on CNN's page has a great cutout of Jupiter's atmosphere with new data.

http://www.cnn.com/2017/05/25/us/nasa-jupiter-juno-mission-observations-first-results/index.html

A question that has been tossed around for a long time is just how far can you go into a GG's atmosphere before your ship gets crushed. According to the infographic, the area between 1km and 100 km reaches 12 bars of pressure. 1 bar = 14.5psi, the pressure at sea level on earth. 12 bars = 174 psi. If you look at things from underwater, every 10m = 1 atmosphere (14.5psi). So depending on what crush depths you want to talk about, you at least have an idea of the depth you are dealing with.

 

[Condottiere]

Are gas giants constantly storming?

Avoid areas of severe weather conditions.

Forecast: thunderstorms.

 

[h1ro]

To say nothing of the orbital speeds you'd be hitting the atmosphere at..

(OK, sorry, I'll get my coat)

 

[Nobby-W]

To say nothing of the orbital speeds you'd be hitting the atmosphere at..

Well, at the cloud tops the gravity of Jupiter is about 2.5g, and the cloud layer has an atmospheric pressure in the region of 0.6-7 atmospheres, depending on how deep you want to dive. To scoop from Jupiter (try not to think too hard about the glow-in-the-dark levels of radiation flux), then you need to cope with about an atmosphere's worth of pressure, or maybe a bit more. Practically, you could fly around doing your refuelling manouevre at perhaps mach 1-2 or so without cooking your spaceship from the compression heating.

Jupiter's escape velocity is about 60km/sec (roughly twice the delta-v needed to drop rubbish into the sun), so you would need to slow down from that to maybe 2km/sec to enter the upper atmosphere without needing extensive heat shielding. It also means you would need to get out of Jupiter's atmosphere without exceeding that sort of speed before you could boost to escape velocity.

Assume a requirement for a manouevre drive capable of 3-4G for gas giant refuelling - unfortunately this doesn't get a mention in the OTU canon.

 

[AnotherDilbert]

Don't go so deep into the atmosphere. At higher altitude you will find lower pressure, so less air resistance, and lower gravity, so lower escape velocity.

 

[MongooseChris]

Well, at the cloud tops the gravity of Jupiter is about 2.5g, and the cloud layer has an atmospheric pressure in the region of 0.6-7 atmospheres, depending on how deep you want to dive.

So you'd be hard-pressed in your little 1G acceleration free trader to not fall into the gas giant unless you really stress those engines to get out. I guess I'd find it hard to believe you could squeeze 3G out of a 1G maneuver drive.

 

[h1ro]

Or you enter the atmosphere at a high enough velocity to exit the gravity well. Could get a little bumpy and I'm sure it would be scary but hey...

And, to the best of my knowledge no version of Traveller has specified how long it takes to fill your tanks.

 

[Nobby-W]

Or you enter the atmosphere at a high enough velocity to exit the gravity well. Could get a little bumpy and I'm sure it would be scary but hey...

Hm. Entering the upper atmosphere of a gas giant at ~60km/sec. What could possibly go wrong?

 

[AnotherDilbert]

And, to the best of my knowledge no version of Traveller has specified how long it takes to fill your tanks.

To skim a gas giant for starship fuel:
Routine, Pilot, Navigation, 1 hour (hazardous).

MT Imperial Enc, p88.
Task duration is 3D × 1 h, so average duration is about 10 h.

In order to refuel from a gas giant, a ship must move into orbit around it and then dive deep into its atmosphere with open fuel scoops. The procedure (called skimming) takes approximately 10 hours and results in fuel tanks filled with unrefined fuel. Skimming is an Average task using Pilot (Interface/Grav).

TNE, p220.

 

[h1ro]

Or you enter the atmosphere at a high enough velocity to exit the gravity well. Could get a little bumpy and I'm sure it would be scary but hey...

Hm. Entering the upper atmosphere of a gas giant at ~60km/sec. What could possibly go wrong?

Yeah, right.

Hahahaha

It's all linked in to the orbital velocity and making planetfall with a grav drive of some kind.

AD is great at pulling answers from previous versions. This is the kind of stuff I'd love to see made current in the Companion but maybe that would make the 2e tied too closely to the 3I. I mean, it is but people don't seem to like saying it.

 

[phavoc]

If your ship has 1G drives and contragravity you will always be able to escape the gravity well (up to the point your anti-gravs are overwhelmed, or your hull is crushed due to pressure). The drive will continue to add speed and you just do an orbital transfer until you've built up enough speed.

 

[h1ro]

It's the "if" that I'm talking about

It's fine that this stuff is left for individual groups to decide for themselves, it also makes sense to me that it should be included with setting info.

 

[phavoc]

I'm ready for ANY of the editions of Traveller to detail out 'High Guard' gas giant operations and why everyone is scared about 400ton SDB's lurking in the clouds that can ruin an incoming fleet's day.

 

[AnotherDilbert]

... 400ton SDB's ...

SDB can be much larger with better armament than a few turrets. "Boat" just means no jump drive.

 

[Nobby-W]

If your ship has 1G drives and contragravity you will always be able to escape the gravity well (up to the point your anti-gravs are overwhelmed, or your hull is crushed due to pressure).

That does pre-suppose your AG drives are capable of generating 2.5G of thrust, which uses quite a lot of power per Striker or FFS. In practice, I suspect nobody at GDW ever did the maths for this and if they did certainly never wrote it down or codified it in a rule book.

 

[Condottiere]

You can probably do it on anti gravity alone.

I don't know about dirtside vehicles, but my estimate would be factor nine at technological level thirteen for spaceships.

 

[Nobby-W]

... 400ton SDB's ...

SDB can be much larger with better armament than a few turrets. "Boat" just means no jump drive.

The 400t SDB from the original Traders and Gunboats had nuclear missiles and a fairly decent computer for a TL12 ship. If you were not able to use agility while refuelling then your ships could be vulnerable to nuclear missiles. However, the specifics were never ruled in depth - I don't think either High Guard or TCS discussed this beyond a vague notion that you couldn't refuel at a gas giant that had hostile SDBs present unless you first cleared out the SDBs.

 

[AnotherDilbert]

The 400t SDB from the original Traders and Gunboats had nuclear missiles and a fairly decent computer for a TL12 ship. If you were not able to use agility while refuelling then your ships could be vulnerable to nuclear missiles. However, the specifics were never ruled in depth - I don't think either High Guard or TCS discussed this beyond a vague notion that you couldn't refuel at a gas giant that had hostile SDBs present unless you first cleared out the SDBs.

I agree agility should be unavailable, and some surprise should apply.

A factor 3 missile battery will not penetrate a 6+ nuclear damper, less with a good computer, and non-nukes will not do much to armoured ships. TL13+ warships or so will not be affected, but unarmoured auxiliaries, tankers, tenders, and transports will be very vulnerable.

We need bays to really hurt high-tech warships.

 

[Condottiere]

At four hundred tonnes, you can certainly fit one in.

In fact, without accommodating a jump drive, it's hard to justify not having one in a warship at that size.

 

[Reynard]

I think the original SDB designs were harassers going after support craft because an army travels on its stomach. They also were probably good in numbers picking off escorts opening up larger ships to attack by their enemy's equivalent. I would say there are many designs specifically as an attempt to take on larger vessels at a cost both in budgets and reducing the SDBs prime advantage, numbers. PT boats in space.

I'm sure one of the vast number of Traveller books or magazines from the past has information about gas skimming. Best and immediate source for such info is T5 in the world generation section. It gives actual sizes for a system's GGs from size 20 (little smaller than Neptune) to 32 (Brown dwarves). To skim them, your ship's maneuver Gs must equal or exceed GG size/100 ( I think they meant 10). This might mean Free Traders can't use GGs and you need 4gs for skimming size 31 or 32 GGs. Interesting limitation, a system can have gas giants you can't use. Your Free Trader scoops and processors are good only for water.