CT Only: Spinward Yacht

[Fovean]

Fighting gravity is fun

For gas giant fuel skimming, you can use 2G to skim Saturn, Uranus and Neptune "type" gas giants ... but if you want to skim for fuel at a Jupiter "type" of gas giant, you're going to need at least 3G (otherwise your de-orbit for fuel is going to be a one way trip!). :toast:

This isn't something explicitly spelled out in the Traveller rules (as written) anywhere ... this is me looking around and applying a bit of "game reality testing" to the proposition.

I think it’s great you’re thinking this way! My gang and I have been playing with this paradigm for quite a while now. It’s made the canonical High Guard maneuver actually a thing IMTU, and as you say, it makes the crew think about where they want to go for their free fuel… gives each star system some unique terrain considerations.

Fair warning, it doesn’t seem to be a very popular idea I’m afraid.

Regardless, I like the ship you’ve come up with. If I have time this weekend I might be able to stat it up for MgT 2e and have a better look at it (haven’t played with LBB rules in umpteen years so my CT-fu is quite weak).

 

[Spinward Flow]

I think it’s great you’re thinking this way!

It's also why I turned on the "maximum verbosity" with my original post, so as to provide transparency into the thinking behind the decisions. Even if you're really experienced with the rules (and how to bend them, and why you would want to), sometimes you just look at what someone does with a set of ship design stats and the only thing you can ask yourself is ... why do it THAT way??

So as advertised, I wanted to provide clarity on the thinking behind the decisions so that Referees (and Players who want to pester them!) have access to that thinking, can ask questions, draw their own conclusions and judge for themselves whether the notions behind the ideas have merit. That way you don't just have to take my word for it ... you can be your own judge.

My gang and I have been playing with this paradigm for quite a while now. It’s made the canonical High Guard maneuver actually a thing IMTU, and as you say, it makes the crew think about where they want to go for their free fuel… gives each star system some unique terrain considerations.

Aye.
I was lurking these forums, reading through old posts (went back to the beginning of The Fleet forum!) to get a feel for the community here, see if I could grasp the sensibilities of ship designers (past and present) and kept noticing the same blinkered thinking when it came to civilian ship designs (most of which were merchant traders, with the occasional yacht or safari ship thrown in). Most of the discussions were about Jump-1 versus Jump-2 (and Jump-3) economics, how to turn a profit with the standard merchant designs from LBB2, and so on ... and when people were "optimizing" those designs for bulk cargo hauling I would see 1G maneuver drives basically every time.

Now the reason for this pattern in practice isn't that hard to figure out.
Until LBB6 expanded the star system generation rules, every single star system had either 1 or 2 worlds in it to be bothered with ... the "mainworld" and the gas giant (if present). That was it. When reduced to the UWP code, each system basically only had 1-2 places to go (and one of those might be optional!).

When you can jump in to a system near 100+ diameters away from the only place in the parsec worth visiting (due to a lack of detail for other worlds/moons in system), there's basically no point in interplanetary travel ... except maybe to go to a gas giant (wherever that might be, handwave) to refuel ... and leave. When there's only 1 place you NEED to visit, there's only one place you're going to go, and if you only need 1G to get "there" in an hour or two, why would you ever need anything more than 1G?

Or if you'll forgive the more appropriate Star Trek quote ... this pattern indicates two dimensional thinking ...

However, once you start thinking more expansively ... using LBB6 expanded rules for star system generation, where you have orbits and can have multiple populations on different worlds/moons within a single parsec ... suddenly, interplanetary travel (and travel times!) can start becoming an important consideration. When you have motivation to GO to more than 100 diameters beyond the location where you jump into a star system, having more than a 1G maneuver drive suddenly increases in value! The problem is ... the Referee needs "details" on all of those other places beyond the "mainworld" in order to make that happen, and the basic UWP found in places like LBB S3 Spinward Marches doesn't do that.

SOME of the star systems found through the online Traveller Map contain this additional system information ... but it's RARE ... mainly because it's a LOT of work to use LBB6 to "finish out" a single star system. It can be rewarding to do so, if that's your thing, since the LBB6 system contains SO MUCH DETAIL(!) o: ... but not every Referee has the time to devote to that purpose (and if your Players "leave the neighborhood" and don't come back, wasn't all that time and effort wasted?).

So there's a sort of "two dimensional bias" in thinking about starships. We tend to only look at hex maps of parsecs and by default think there's only one "mainworld" in each system as detailed by the UWP for that world. The only travel between worlds is interstellar ... because there are no other worlds detailed in each system beyond the "main" one in almost all cases. There are exceptions, of course, but those are so rare that it's hard to build up a campaign setting around just them alone (ala Firefly, which was interplanetary only, not interstellar). That in turn reinforces the idea that maneuver drives are "superfluous" items that only matter in combat (if then), but otherwise don't add enough value to want to have more than the stock 'n' standard 1G minimum, so as to have more room for "important stuff" like passengers and cargo that can earn money.

Well, if there's no compelling REASON to have anything more than a 1G maneuver drive in a commercial ship, there aren't going to BE any ship designs with more than a 1G maneuver drive.

At which point, it's up to the Referee to look around ... and see if there are any compelling reasons for why using a 1G maneuver drive might not always make sense ... aside from needing to run away from pirates, of course.

Fair warning, it doesn’t seem to be a very popular idea I’m afraid.

Nor do I expect it to be. I would expect the default stance to be one of "if 1G was good enough for LBB2 ships made in 1977 then it's good enough for me today!" since there is a very definite COST involved in bumping up maneuver drives on ships (in both tonnage and MCr). It doesn't help that most of the "standard" hulls of LBB2 fame simply won't allow drive compartments large enough to fit much more than Jump-1, Maneuver-1 and Power Plant-1 within their preset limits before needing to resort to custom hulls, which then reinforces the basic notion that 1G maneuver drives MUST be "just fine" and perfectly reasonable ... pretty much everywhere. I mean, they're STANDARD for a reason ... right?

Regardless, I like the ship you’ve come up with. If I have time this weekend I might be able to stat it up for MgT 2e and have a better look at it (haven’t played with LBB rules in umpteen years so my CT-fu is quite weak).

Feel free.
If what I do inspires you to come up with something that you wind up using in a campaign with your Players, then I can consider my efforts in this area well repaid.

 

[AnotherDilbert]

True.
Except that LBB2.81 p13 stipulates a minimum of MCr20 price for metal hulls, and LBB5.80 p 18 stipulates that LBB2 is not superceded by any system given in LBB5.80. So I take that as a minimum MCr 20 price for the hull, regardless of configuration, and the fuel scoops get added on top of that (Cr 1000 per ton of ship) because, like you said, those are only free on small craft.

No, you are not using both systems at once. They are just saying that you can use either the LBB2 system or the LBB5 system in parallel. Specific LBB2 rules like that do not apply to LBB5 ships.

Look at the design example for the fighter "Gnat":

Its hull masses 8.5 tons and uses the close structure configuration (8.5 tons; MCr0.51).
...
The fighter mounts three weapons (1 ton): one sandcaster for one factor3 battery (MCr0.25; no energy points), one laser for one factor 2 battery (MCr1; 1 energy point), and one missile rack for one factor-2 battery (MCr0.75; no energy points).

No minimum hull cost, no separate turret cost.

I have an answer to that, previously posted.
...
For gas giant fuel skimming, you can use 2G to skim Saturn, Uranus and Neptune "type" gas giants ... but if you want to skim for fuel at a Jupiter "type" of gas giant, you're going to need at least 3G (otherwise your de-orbit for fuel is going to be a one way trip!). :toast:

No, you don't stop and "land" on (in?) the gas giant. You just pass through it's upper atmosphere. You are never really leaving orbit, you just use an elliptical orbit that dips into the GG atmosphere for a while, then curves out again. A 1 G spacecraft can skim any gas giant.

Gas Giant Fuel Skimming
A ship which moves to a layer of gas giant atmosphere which contains clear H2 can fill its fuel tanks at the standard rate for its scoops. A ship in a layer other than clear H2 can fill its fuel tanks at half rate.
Gas Giant Fuel Skimming is orbital in nature; the ship is not landing and restrictions based on drive acceleration do not apply.

Something like this:


Note: Fuel is free, but ship time costs a lot more than fuel. The mortgage cost during the time you cruise to a GG is generally much more expensive than fuel. Unless the world you are visiting is orbiting a GG, or you are just passing through the system (not stopping by the starport), GG skimming is rarely worth it. Naval fleets passing through, sucking vast amount of fuel RIGHT NOW might disagree.

I mean that GG skimming is a thing for the Navy and Scouts, but not generally for civilians.


A ship with 1 G will have a problem landing on a planet with a surface gravity of 1 G or higher (~size 8+). 2 G or 1 G + wings and a long runway are needed, lest you be restricted to the highport.

I think in Mongoose we can count "Streamlined" configuration as wings or equivalent lift. Still need a massive runway to land a 1 G ship.

So, in my opinion, 2 G is very useful, 3 G is a marginal upgrade outside combat.

 

[AnotherDilbert]

It isn't strictly speaking a "backup drive" combination, but more of a "tandem drive" cooperative situation, which CT doesn't account for all that well since most of the combinations don't add up right for one reason or another.

It isn't unreasonable, but explicitly banned in CT.

Mongoose allows exactly this (Breakaway Hulls) but at a bit of surcharge.
T5 allows Nexus.

Please misunderstand me correctly: I'm not saying you can't do it, I'm just saying it would be a house rule. That is why I added that it is explicitly allowed in later rule sets.

E.g. there are no rules in CT for building a Modular Cutter, yet there it is.

 

[Spinward Flow]

No minimum hull cost, no separate turret cost.

Okay then, modifications incoming.

No, you don't stop and "land" on (in?) the gas giant. You just pass through it's upper atmosphere. You are never really leaving orbit, you just use an elliptical orbit that dips into the GG atmosphere for a while, then curves out again. A 1 G spacecraft can skim any gas giant.

T5.10, Book 2, p103
Gas Giant Fuel Skimming
A ship which moves to a layer of gas giant atmosphere which contains clear H2 can fill its fuel tanks at the standard rate for its scoops. A ship in a layer other than clear H2 can fill its fuel tanks at half rate.
Gas Giant Fuel Skimming is orbital in nature; the ship is not landing and restrictions based on drive acceleration do not apply.

Something like this:

I see that your reference is sourced from T5.
No such information is to be found anywhere I have looked inside of CT LBB sources (which is what I'm using).

The first thing I thought of when seeing that orbital plot was "aerobraking" so I went to look up the rule for aerobraking on LBB2.81 p34 and found that the way the rule is structured for the vector math system of LBB2 style movement is that aerobraking produces a 0.1g drag force (10mm of vector, when 100mm equals 1G maneuver) which can easily be compensated for by a 1G drive. But the aerobraking rule is only invoked when within 1000km of an atmosphere type of 6+ (LBB2 was rather simplistic back in those days).

So I guess a 1G maneuver drive could skim Jupiter then ... just pay attention to your orbit when you're doing it and apply thrust to compensate for the atmospheric drag (because if there's atmosphere enough to scoop, there's atmosphere enough to drag!). Although ... LBB S3, p36-37 details that starships which are not streamlined (configurations 1, 2 and 6) cannot land through an atmosphere type greater than 1 (trace). The cross-correlating understanding being that gas giant fuel skimming is supposed to be happening at the trace atmosphere density region (as opposed to "very thin" or denser atmosphere depth regions). So definitely an "upper atmosphere" type of maneuver where you are NOT expecting to plunge into the cloud layer, but rather to fly through the "trace" density region well above the cloud "surface" layer of a gas giant while remaining orbital. Maintenance of that orbital path will require at least 0.1G of maneuver to be available, otherwise the orbit will decay over successive passes through the atmosphere.

Because orbital mechanics "are weird" compared to how things move around down on terra firma, applying thrust (or drag) on one side of an orbit actually changes the path of the opposite end of the orbit. So using AnotherDilbert's image to illustrate this point:



If you don't compensate for the (trace) atmospheric drag on the left, the height of the orbit path on the right will be lowered. Let this happen too many times in a row without compensation and your orbit will decay due to drag in such a way as to "tighten" enough to drag your ship down into the atmosphere. So using this image, uncompensated drag on the "left" of that orbital path results in a reduction in the altitude of the orbital path on the "right" of that image ... until an orbital path above the atmosphere can no longer be sustained and then you just spiral down (the drain) into the atmosphere. :toast:

Note: Fuel is free, but ship time costs a lot more than fuel. The mortgage cost during the time you cruise to a GG is generally much more expensive than fuel. Unless the world you are visiting is orbiting a GG, or you are just passing through the system (not stopping by the starport), GG skimming is rarely worth it.

In the Time Is Money™ sense, this is most definitely true. With a low maneuver drive rating (let's call it 1G for conversation purposes ), it is perfectly possible for the time it takes to maneuver to and skim a gas giant to wind up costing more in operational expenses over that time frame (bank financing, life support, crew salaries, annual maintenance set asides) than the more direct cost of simply buying fuel (refined or not) from a starport.

To get an answer to THAT question, you'll need to drill all the way down from an "operating costs per 2 weeks" standard all the way down to an "operating costs per hour" equivalency so as to determine a "break even" point between spending time on interplanetary travel or on simply buying fuel at the starport (type D or better) or spaceport (type G or better, LBB6 p26). Calculate the cost to buy fuel and then divide that cost by the "operating costs per hour" value you calculated earlier to figure out how many hours of ship operation cost as much as buying fuel at the port. Subtract 6 hours from the total number of hours you've calculated (to account for time spent skimming fuel) ... and there's your answer for how many hours you can spend maneuvering to reach "free" fuel instead of purchasing fuel. Once you know how long you have to "spend" on interplanetary travel like that, you can calculate how far you can go with your maneuver drive using LBB2.81 p10. That then lets you know if your "legs are long enough" to reach "free" fuel more cheaply than simply buying it.

And it's at THAT point that having a more powerful maneuver drive (2G, 3G, etc.) changes the economic calculus on the Time Is Money™ scale for this kind of thing, since more maneuvering "power" increases the range at which it is cheaper to skim for fuel at a different planetary orbit than the mainworld than buying fuel from the starport or spaceport (bigger maneuver drives have a wider "reach" range for cheap(er) fuel). So the value of a more powerful maneuver drive "still stands" ... but not for the reason I was advocating for earlier (less important "at" the planet, more important "between" planets) when it comes to 2G vs 3G.

2G maneuver is needed for Streamlined configurations (1, 2 and 6) to liftoff and break orbit from UWP world size codes 8+ ... while also being adequate for gas giant skimming ... but the interplanetary travel time can itself become an economic factor in evaluating Time Is Money™ equivalencies. These considerations will vary for every space vessel and the (intended) route they plan to navigate.

So, in my opinion, 2 G is very useful, 3 G is a marginal upgrade outside combat.

Kind of like jump drives, eh wot?
Going from 1 to 2 is a HUGE gain in flexibility of course plotting (for both jump and maneuver!) ... but going from 2 to 3 is not as much of a gain as going from 1 to 2. There is a decline in efficiency gains and drive power increases.

The 1 to 2 increase can enable certain threshold performance levels to be reached/exceeded at 2 that simply aren't possible (or reliably practical) at 1. The 2 to 3 increase does this again, but the increase in the range of use cases is less than the increase from 1 to 2.

And yes, if it wasn't already obvious, I am thoroughly enjoying this conversation.
It is giving me greater perspective on a wide range of issues that are only implied by the starship design rules, so this is very Taking It To The Next Meta Level™ interesting for me.

Please misunderstand me correctly: I'm not saying you can't do it, I'm just saying it would be a house rule. That is why I added that it is explicitly allowed in later rule sets.

E.g. there are no rules in CT for building a Modular Cutter, yet there it is.

Exactly. Hence the explanation as originally given to enable precisely that sort of house rule understanding with the Pinnace version.

 

[whartung]

I've never views gas giant skimming that way. I never felt that the ship was "skipping" off of the atmosphere.

The ship is powered, and simply "bulldozing" its way through the atmosphere.

Heck, they can just park, station keep, open the valves and start pumping. "Gas Giant dipping" in that case.

That orbital skipping plot is just too inefficient.

Now, maybe, just maybe, you can make a case for this style of fuel in particularly egregious discrepancies between M Drive power and the gravity well of the gas giant, where the ship relies on the orbital momentum to escape the planet.

But I've never put much stock that orbital ships with 1G drives are underpowered for this maneuver, especially with all of the handy wavy contra grav "sorta" "maybe" shenanigans posited over the years across the different rule systems.

 

[Spinward Flow]

Update to the configuration 6 starship only version of the Spinward Yacht now complete.

Changes limited to:
Reduction of hull cost (MCr 20.2 down to 16.2) as recommended by AnotherDilbert
Removal of hardpoint and triple turret cost (MCr 2.2 down to 0) as recommended by AnotherDilbert

Purchase price, architect fees, down payment, annual maintenance cost and bank financing info all updated, along with USP "code block" info to match.

I'm retaining the 3G maneuver drives as a consideration for fast(er) interplanetary travel in campaigns where system data for worlds and moons beyond the "mainworld" are available. Interplanetary travel is sadly all too often overlooked and discounted by Referees and Players alike, who prefer to focus on interstellar travel instead. I may explore a 2G downgrade version later in order to reclaim the auditorium (in SPAAAAACEEE!!!) luxury feature at another time.



Right now, I'm using some of the deeper understandings learned from the conversations in this thread to settle on a design for a Jump-6 (with L-Hyd Drop Tanks) Express Boat, Express Boat Tender and Armored Gig (slash XBoat Tug) combination that could be used for the announced Jump-6 XBoat upgrade that was one of the triggering events for the Fifth Frontier War, per CT canon. One of the outcomes of this effort is a subtle rebalancing of the hangar bay, cargo hold, fuel tankage, crew complement and passenger accommodations tonnage allocations inside the 1000 ton displacement limit.

First thing I'm noticing about the TL=15 J6 XBoat system I'm designing?
It's going to be a LOT harder for Pirates to capture and compromise/convert XBoats and Tenders into Corsairs ... thanks to the added (mobile!) security of the Armored Gigs for fighter escort as well as tug duty in helping recover XBoats after breakout from jump space. The Tenders also have more crew aboard (for, reasons...) making them harder targets to capture through boarding actions.

Not impossible for a pirate capture to happen, of course ... but certainly a lot harder to succeed at and require a larger commitment of resources to even attempt than with the older TL=10 J4 XBoat and Tender series, due to a combination of factors.
I mean, the Third Imperium wouldn't want to have all their shiny new TL=15 interstellar communications network technology getting stolen out from under their noses now, would they? :coffeesip:

 

[Spinward Flow]

I've never views gas giant skimming that way. I never felt that the ship was "skipping" off of the atmosphere.

The ship is powered, and simply "bulldozing" its way through the atmosphere.

Heck, they can just park, station keep, open the valves and start pumping. "Gas Giant dipping" in that case.

That orbital skipping plot is just too inefficient.

Now, maybe, just maybe, you can make a case for this style of fuel in particularly egregious discrepancies between M Drive power and the gravity well of the gas giant, where the ship relies on the orbital momentum to escape the planet.

And that's where life gets interesting, isn't it?

There's more than one way to perform this manuever ... using an orbital skim through the atmosphere (keep moving) ... or a park and dip in the atmosphere (stop moving). The orbital skim would presumably "ram" shock at orbital velocity to skim some fuel, but might need more than one orbit to accumulate sufficient fuel tankage. The park and dip would be capable of descending lower into the atmosphere (safely) to draw fuel from a higher density layer, so literally trading off movement speed for flow rate.

The difference between the two methods would almost certainly be measured in how quickly the fuel tanks can be topped up, with the park to dip method being faster than the orbit to skim method. However, the park to dip option would require more acceleration capacity out of the maneuver drive to do (so as to "hover" against the gas giant's native gravity pull).

So while a 1G maneuver drive CAN skim fuel from a gas giant on an orbital trajectory, it might not be able to do so AS FAST as can be done with a 3G maneuver drive pulling a park to dip refueling action. The orbital skim might require more than one orbit to fill the fuel tanks, while the park to dip would only need one trip into and out of the atmosphere to complete.

Needless to say, CT LBB are remarkably "silent" on all of this ... aside from the occasional wink, nod and handwave in vague directions.

Good times.

But I've never put much stock that orbital ships with 1G drives are underpowered for this maneuver, especially with all of the handy wavy contra grav "sorta" "maybe" shenanigans posited over the years across the different rule systems.

Depends on how you like to interpret things I guess. Different people (Referees) tend to see things differently ... or so I've been led to believe on occasion.

 

[whartung]

And that's where life gets interesting, isn't it?

There's more than one way to perform this manuever ... using an orbital skim through the atmosphere (keep moving) ... or a park and dip in the atmosphere (stop moving). The orbital skim would presumably "ram" shock at orbital velocity to skim some fuel, but might need more than one orbit to accumulate sufficient fuel tankage. The park and dip would be capable of descending lower into the atmosphere (safely) to draw fuel from a higher density layer, so literally trading off movement speed for flow rate.

Well, also, what's not discussed, is the liquifying process. The tanks aren't holding gaseous hydrogen, but liquid hydrogen. So, there's a compression/cooling phase that's necessary to get the fuel in to the tanks. That means in a "skimming" scenario, you need to have an extra tank to skim gas in to, and then draw out as a liquid to store in the fuel tanks, since the actual skimming process may not be long enough for processing to happen. I have no idea how fast the gas -> liquid process takes.

Different people (Referees) tend to see things differently ... or so I've been led to believe on occasion.

Yea I think I've heard that too.

 

[AnotherDilbert]

Kind of like jump drives, eh wot?
Going from 1 to 2 is a HUGE gain in flexibility of course plotting (for both jump and maneuver!) ... but going from 2 to 3 is not as much of a gain as going from 1 to 2. There is a decline in efficiency gains and drive power increases.

Certainly, you get diminishing returns, but it's still much better for J-drives.

If you want to jump six Pc, it would take three jumps (weeks) with a J-2 drive and two jumps (weeks) with J-3 drive.

If you want to travel a billion km (a reasonable distance to a GG) it would take 5 days with a M-2 drive and 4 days with a M-3 drive, not much of a difference.

A million km (normal 100D trip) takes 4 h with a M-2 drive and a bit over 3 h with a M-3 drive, not normally significant or noticeable.

 

[AnotherDilbert]

Heck, they can just park, station keep, open the valves and start pumping. "Gas Giant dipping" in that case.

... or a park and dip in the atmosphere (stop moving).

What is "park"? How can an aircraft "park" on a cloud?


Speed is what you get when you dive into the gravity well. Speed is energy. Energy is what you need to get back out of the gravity well.

The slower and deeper you go in the gravity well, the more difficult it is to get out again. Why would you skim the most difficult way possible?

 

[robject]

Please misunderstand me correctly

OH MY GOSH, THIS SHALL BE MY GO-TO PHRASE FOR 2021!

 

[Grav_Moped]

Just to clarify a point about skimming on an orbital trajectory (though it's probably obvious): with unlimited delta-v, ships don't have to go around the whole elliptical orbital path again to make a second pass at the atmosphere. As long as the ship's vector and atmospheric entry angle at the point of atmospheric entry are identical to what they would have been at that point on the appropriate elliptical orbit, the geometry and physics are the same.

My math-fu isn't up to figuring out whether this just lets you turn the elliptical orbit into a pointy egg-shape with 1G acceleration, or whether 1G allows you to get back into the atmosphere again at the correct angle and speed before going all the way around again.

 

[Condottiere]

Figured out years ago that gas skimming wasn't commercially viable if someone was selling raw hydrogen at destination; which is where the investment in a fuel processor pays off.

If the gas giant isn't turned into a military reservation, I'd bet that some corporation would set up a claim on the resources, probably heavily bribing local politicians, and run off any one wanting to dip their dry wick, or wetting their beak.

 

[AnotherDilbert]

So I guess a 1G maneuver drive could skim Jupiter then ... just pay attention to your orbit when you're doing it and apply thrust to compensate for the atmospheric drag (because if there's atmosphere enough to scoop, there's atmosphere enough to drag!). Although ... LBB S3, p36-37 details that starships which are not streamlined (configurations 1, 2 and 6) cannot land through an atmosphere type greater than 1 (trace). The cross-correlating understanding being that gas giant fuel skimming is supposed to be happening at the trace atmosphere density region (as opposed to "very thin" or denser atmosphere depth regions). So definitely an "upper atmosphere" type of maneuver where you are NOT expecting to plunge into the cloud layer, but rather to fly through the "trace" density region well above the cloud "surface" layer of a gas giant while remaining orbital.

According to T5.10 B3 p90 Trace is about 10 km or the start of the troposphere in a standard atmosphere.


That is about 20 kPa pressure:



In the atmosphere of Jupiter that is just below 50 km over the "surface":

20 kPa = 20 000 Pa = 2 × 10⁴ Pa.


The difference between "Trace" atmo pressure and "Standard" atmo pressure is just roughly 10 km altitude on Jupiter. Both are about 1000 km into the atmosphere. There is simply no real difference in altitude.

 

[Spinward Flow]

What is "park"? How can an aircraft "park" on a cloud?

Speed is what you get when you dive into the gravity well. Speed is energy. Energy is what you need to get back out of the gravity well.

The slower and deeper you go in the gravity well, the more difficult it is to get out again. Why would you skim the most difficult way possible?

Please misunderstand correctly.

 

[aramis]

Heck, they can just park, station keep, open the valves and start pumping. "Gas Giant dipping" in that case.

Only if they have sufficient thrust. Unless using the overthrust rules from MT, or CG from TTNE or T4, doing so with a 1G is a death sentence on a saturnian or larger GG... cloudtop gravity is around 1.08G.

Jupiter is 2.4G, you'll need 2G.

The atmospheric perigee method allows using ram-air, as well; the cloud tops are about 0.1 Bar, but you're going to need much higher to liquify it into the tanks.

 

[Grav_Moped]

Only if they have sufficient thrust. Unless using the overthrust rules from MT, or CG from TTNE or T4, doing so with a 1G is a death sentence on a saturnian or larger GG... cloudtop gravity is around 1.08G.

Jupiter is 2.4G, you'll need 2G.

The atmospheric perigee method allows using ram-air, as well; the cloud tops are about 0.1 Bar, but you're going to need much higher to liquify it into the tanks.

T5 has contra-grav lifters installed as the default.

 

[Condottiere]

Going by Mongoose, you can have several different propulsion systems working at the same time, and they appear to be additive.

Simplest would be lifter (or equivalent, neutralizing some or all of the local gravity field), the manoeuvre drive, and if that's insufficient, rocket afterburners to make up the difference.

 

[Spinward Flow]

Only if they have sufficient thrust. Unless using the overthrust rules from MT, or CG from TTNE or T4, doing so with a 1G is a death sentence on a saturnian or larger GG... cloudtop gravity is around 1.08G.

Jupiter is 2.4G, you'll need 2G.

And this is where the distinction between Large Gas Giants (LGG) and Small Gas Giants (SGG) per LBB6 can become useful.

Worlds/Moons with a size code of 7- require 1G acceleration to liftoff, reach and break orbit.
Worlds/Moons with a size code of 8+ require 2G acceleration to liftoff, reach and break orbit.

Small Gas Giants (SGG) with a radius of 20,000-60,000 km require 2G acceleration to hover in the cloud layers, ascend, reach and break orbit.
Large Gas Giants (LGG) with a radius of 60,000-120,000 km require from 3G to 6G acceleration to hover in the cloud layers, ascend, reach and break orbit.

Saturn is right on the cusp between LGG and SGG in terms of radius (it's about 60,000 km), but due to Saturn's low density (0.687 g/cm³) it's better to classify Saturn as a "big" SGG than as a small LGG to account for the maneuver drive breakpoint between 2G and 3G for hover and liftoff performance. It just makes the classification system simpler that way for a Referee to use.

Jupiter is about 70,000 km radius, so definitely a LGG using the Traveller rules definition, but a "small" LGG as far as the classification is concerned.

So with all of that in mind, you wind up with the following UWP coding shorthand for the Terra system:

• Large Gas Giants (LGG): Jupiter
• Small Gas Giants (SGG): Saturn, Uranus, Neptune

This then roughly corresponds with the amount of maneuver drive you would need to "hover and dip" fuel from them, as opposed to using the "orbital ram skimming" maneuver.



Always nice when you can make reality fit the rules.