Gas giant refuelling

[phavoc]

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.

This goes against the main idea of contragravity - up to the limit it functions that is. While it won't help with escape velocity, your 1G drive will build up enough thrust over time to help you escape the gravity well.

 

[h1ro]

It sounds like, tho I don't have the stamina to actually look thru T5, that the M drive is allowing the ship to ignore a certain amount of gravity, higher the rating, more it can do. I quite like the idea.

It also sounds like skimming is done at low speed and therefore the idea that you could dive into the atmosphere with enough velocity to pop out the other side isn't the way it's done so your low M drive ships aren't gonna be refueling that way. They would be reliant on standard G planets with oceans.

The time to skim I'd also think would be related to your ship's ability to process the incoming gas. The gas taken in thru scoops has a higher volume than the liquid hydrogen it becomes and therefore you can only complete skimming as fast as you can process the fuel.

Makes unrefined fuel bought at your friendly local starport sound really attractive.

 

[AnotherDilbert]

This goes against the main idea of contragravity - up to the limit it functions that is. While it won't help with escape velocity, your 1G drive will build up enough thrust over time to help you escape the gravity well.

CT, MT, and MgT ships don't normally use contragrav or even a-grav.

 

[h1ro]

Mongoose has said what or how things that mass lots fly?

OK, they haven't listed mass on any designs but you know what I mean!

 

[phavoc]

This goes against the main idea of contragravity - up to the limit it functions that is. While it won't help with escape velocity, your 1G drive will build up enough thrust over time to help you escape the gravity well.

CT, MT, and MgT ships don't normally use contragrav or even a-grav.

I don't recall ever seeing passages in the core or ship books that explicitly state that. But i also haven't seen the opposite either. However I don't see how they would NOT have it, based upon starport descriptions and many illustrations. M-drive works for getting around, but not for getting up/down. If you have contragravity for vehicles and people (and your loaders), why in the world would you NOT have it for your starships?

 

[Reynard]

MegaTraveller uses anti-grav modules also known as gravitic drive as the TL9 maneuver drive replaced by thruster plates above TL 9. The ship AG modules are much more powerful versions of vehicle AG mods. AG depends on gravitons and limits travel within gravity wells, the more powerful the further a vehicle can be from world. This is why non-ships can't venture much beyond orbit.

Contra-grav, a type of lifter, is in Traveller: The New Era and slightly different in Marc Miller's Traveller. It's used for landing and take off by neutralizing 99% of a world's gravitational. The thrusters actually provide lift and thrust. This system allows even a 1g drive to operate in any gravity well.

 

[AnotherDilbert]

I don't recall ever seeing passages in the core or ship books that explicitly state that.

CT: LBB2, p28: Gravity describes how ships are affected by gravity as they would not be if they had anti-grav.
MT: Ref Man, p65-66: Locomotion describes M-Drive and grav drive as two separate systems that can both be installed in craft; no standard spacecraft had both, they rely on M-Drives. SSOM, p2-3 describes how in detail; no grav drive.
MgT: HG, p86: Effect of Gravity reprises the movement system from LBB2 including gravity effects that a grav vehicle would not suffer.

If you have contragravity for vehicles and people (and your loaders), why in the world would you NOT have it for your starships?

They cost money, space, and power and are not necessary. From MT we know that a 1 G grav drive for a spacecraft is roughly as large and expensive as an 1 G M-Drive. Why not use a larger M-drive that you can use for more than landing instead?

 

[h1ro]

I wish this conversation would settle on what's in (and not in) Mongoose 2e so we could move forward and actually agree what works best for the current version of Traveller.

Bringing all the old versions into it seems to forever go in circles.

 

[AnotherDilbert]

I wish this conversation would settle on what's in (and not in) Mongoose 2e ...

I don't think MgT2 says anything either way.

A vague hint is that grav vehicles can be operated with the Flyer(Grav) skill whereas spacecraft are operated with the Pilot skill. The skills are not interchangeable and you cannot land a spacecraft with the Flyer skill.

 

[h1ro]

That's my point, maybe this stuff will be covered by the Companion, I somehow don't think it will.

For a lot of gamers, they don't want or need to know the kind of detail we're discussing.

For me, I want to know if my tramp free trader can refuel at the local gas giant, how long it will take and how risky it is.

I know that one referee will wing it or handwave it, that's a perfectly valid option. I'd like there to be a rule or guide about it too, one that you're free to ignore or handwave.

To me, it's that kind of detail that makes the game a SF one.

 

[phavoc]

CT: LBB2, p28: Gravity describes how ships are affected by gravity as they would not be if they had anti-grav.
MT: Ref Man, p65-66: Locomotion describes M-Drive and grav drive as two separate systems that can both be installed in craft; no standard spacecraft had both, they rely on M-Drives. SSOM, p2-3 describes how in detail; no grav drive.
MgT: HG, p86: Effect of Gravity reprises the movement system from LBB2 including gravity effects that a grav vehicle would not suffer.

The question wasn't towards M-drives (that would need it's own thread). It was towards the mechanism that provided lift to a starship. The choices are thrusters or contragravity. Anti-gravity would be much better, in my opinion, than thrusters to provide a ship the ability to maneuver in atmosphere. Being able to offset gravity with a field is better than trying to do so with reaction-type thrust.

They cost money, space, and power and are not necessary. From MT we know that a 1 G grav drive for a spacecraft is roughly as large and expensive as an 1 G M-Drive. Why not use a larger M-drive that you can use for more than landing instead?

Everything aboard a ship costs money & space and power. And lift IS necessary, unless you are using tail-landers. You still need to get off the ground, but more importantly, get ON the ground safely.

M-drives (including the gravitic ones talked about) provide thrust from the rear of the starship. This is evident in the original LBB travel tables and the ones that are also currently in MGT v2. So you'd still need to be a tail-lander to have your M-drives get you down to the ground. And Traveller ships aren't like that.

So this still goes back to the unwritten idea that starships mount anti-grav systems for lift out of gravity wells.

 

[Reynard]

Mongoose keeps a lot of things simple especially with technology. Maneuvers works. It gets you on and off planets and lets you skim gas giants. No need to go micromanagement. It's fun to speculate. If one really need to know details, I was under some impression Mongoose follows the lead of T5 so check the ship construction rules there. Once satisfied, fly those ships.

You might want to read T5 pg. 323 How maneuver works for current insight.

 

[Condottiere]

I think the economic case is that it's cheaper just heading for the nearest starport and buying the fuel; better yet, invest in a fuel processor and buy the raw material, instead of wasting time trying to get a free drink from a gas giant on the opposite end of the star system.

For the system defence boats assigned to lie doggo in the gas giants, my interpretation on orbital drives is that they're the spaceship versions of gravitational motors, so those would be used to conteract the local gravitational field.

As for fast skimming, I'm thinking turbines to compress the hydrogen.

 

[AnotherDilbert]

The question wasn't towards M-drives (that would need it's own thread). It was towards the mechanism that provided lift to a starship. The choices are thrusters or contragravity.

? M-drives are thrusters.

Anti-gravity would be much better, in my opinion, than thrusters to provide a ship the ability to maneuver in atmosphere. Being able to offset gravity with a field is better than trying to do so with reaction-type thrust.

Agrav would be convenient, just as VTOL would be convenient on fighters or airliner, yet it is not necessary. For each nice-to-have convenient feature we choose, we un-choose some payload, whether weapons or cargo,

Everything aboard a ship costs money & space and power. And lift IS necessary, unless you are using tail-landers. You still need to get off the ground, but more importantly, get ON the ground safely.

M-drives (including the gravitic ones talked about) provide thrust from the rear of the starship. This is evident in the original LBB travel tables and the ones that are also currently in MGT v2. So you'd still need to be a tail-lander to have your M-drives get you down to the ground. And Traveller ships aren't like that.

Some spacecraft are tail-landers (Mercenary C), some have wings (Serpent, pinnace, Subbie), and some are conventional tail-pushers that perhaps are more graceful in space. SSOM, p2-3 describes in detail how tail-pushers land without wings or agrav. Yes, they descend on their thrusters.

So this still goes back to the unwritten idea that starships mount anti-grav systems for lift out of gravity wells.

I have never seen this assumption, unwritten or written, before TNE. SSOM says otherwise.

Can you point to a specific part of canon where that is described?

 

[Reynard]

"Can you point to a specific part of canon where that is described?"

In Mongoose specifically or in the sources I listed in my two earlier posts?

 

[phavoc]

? M-drives are thrusters.

True, but they are thrusters in the rear of the craft that push the craft forward. As you cited in your example of SOM, the thruster plates are pushers. Pg 2 of SOM has an illustration that shows thruster plates can only provide thrust in a single direction. They can, however, be located anywhere (that fits the description of the Broadsword, as they are located in 4 separate places, all pointing aft) on a ship's hull, but again if you look at the artwork engines are always depicted in the aft section.

Some spacecraft are tail-landers (Mercenary C), some have wings (Serpent, pinnace, Subbie), and some are conventional tail-pushers that perhaps are more graceful in space. SSOM, p2-3 describes in detail how tail-pushers land without wings or agrav. Yes, they descend on their thrusters.

Of the core set of ships published in the editions, the Broadsword is the only one to be a tail sitter. The wings on the starships in question would be of limited use for lift-purposes as the mass of the vessel would negate any sort of lift unless it was moving at very high speeds. And even then it would be insufficient to allow it to lift off (not to mention it would require a runway and wheeled landing gear.

Smaller vessels like the Shuttle would be better suited, but still their mass would preclude the wings providing enough lift to take off like an airplane.

I have never seen this assumption, unwritten or written, before TNE. SSOM says otherwise.

Can you point to a specific part of canon where that is described?

"Can you point to a specific part of canon where that is described?" In Mongoose specifically or in the sources I listed in my two earlier posts?

According to SOM, thruster plates are able to 'push' at an angle, though with much reduced efficiency. They are also capable of reverse thrust (i.e. braking) at like .1 percent of their output. It was at this point that I thought the designers were trying to stretch the idea too far, especially since it seemed to go against their other explanation.

FF&S for TNE pg 13 lists "Also included under this heading is the addition of lifter technology as required for movement on or near a planet. This is particularly the case for spacecraft in the Imperial space campaign, which use contra-grav lifters. See the lifters chapter (section 10).

Pg 75 of FF&S gives more detail, but "Many spacecraft have contra-grav lifters as fuel-efficient means of landing and taking off from a planet surface, and CG lifters are also used on grav vehicles. CG lifters do not provide thust... it goes on to talk about buoyancy instead of actual lift, but the effect is the same.

Look at the cover of the GURPS Starships book and you'll see the port layout and starships in hovering mode indicating a requirement for vertical ascent and descent. A Type S is seen with it's gear down that one can assume it is either lifting up or going down.

Breaking out my old Judges Guild 50 starports shows the layouts of most all of the starports to require vertical lift/descent in order to get to the landing pads.

In the real world the creation of thruster pods has been a boon for most ships. They no longer need tugs for the most part and they can spin in place or make much more radical maneuvers than with the propellers mounted aft only.

It's an aggravating oversight that it's not actually directly mentioned, but it's just one more oversight in a long line of things that I think could have been better defined, either in a core book or in one of the many supplements that have been published over the decades. It's been danced around but never addressed.

 

[AnotherDilbert]

The question wasn't towards M-drives (that would need it's own thread). It was towards the mechanism that provided lift to a starship. The choices are thrusters or contragravity.

? M-drives are thrusters.

True, but they are thrusters in the rear of the craft that push the craft forward. ...

I don't see your point? You said it was not a question of M-drive, but agrav or thrusters. As far as I can see thrusters are M-drives.

Of the core set of ships published in the editions, the Broadsword is the only one to be a tail sitter.

Expess Boat Tender, Sloan, AHL?

The wings on the starships in question would be of limited use for lift-purposes as the mass of the vessel would negate ...

We only have illustrations of the "artists impression" type, not engineering drawings. They clearly show wings.

The hull is streamlined and features variable-sweep airfoils for atmospheric maneuvering and landings.

JTAS2, Serpent Class

I have never seen this assumption, unwritten or written, before TNE. SSOM says otherwise.

Can you point to a specific part of canon where that is described?

According to SOM, thruster plates are able to 'push' at an angle, though with much reduced efficiency. They are also capable of reverse thrust (i.e. braking) at like .1 percent of their output. It was at this point that I thought the designers were trying to stretch the idea too far, especially since it seemed to go against their other explanation.

Yes, so agrav is not commonly used or necessary? I agree the explanation is somewhat contrived, but it is canon I believe.

FF&S for TNE pg 13 lists ...

I certainly agree TNE spacecraft use contragrav, but TNE changed the M-drive completely so I don't think it says much about earlier editions. I think this discussion started with:

CT, MT, and MgT ships don't normally use contragrav or even a-grav.

It's an aggravating oversight that it's not actually directly mentioned, but it's just one more oversight in a long line of things that I think could have been better defined, ...

I agree many things could have been defined better, not that much more would fit in the LBBs. Something like the SSOM but for grav vehicles would have been nice.

 

[h1ro]

We only have illustrations of the "artists impression" type, not engineering drawings. They clearly show wings.

Was a standard ever laid down to advise how each artist drew the ships?

Seems unlikely. With that in mind, the pictures and deck plans give us no standard to work from.

I don't own the Starship Operators Manual from MT, given the prices its demanding on ebay, I am unlikely to own it and there doesn't appear to be a scanned version on DTRPG (Maybe that's to do with the Sanger thing, I dunno and know very little about it) but it seems to be a popular reference for this kind of discussion. Anyone know where I can get a copy at an affordable price?

 

[AnotherDilbert]

"Can you point to a specific part of canon where that is described?"

In Mongoose specifically or in the sources I listed in my two earlier posts?

In CT, MT, or MgT, please.

The drive paradigm changed considerably with TNE.

MegaTraveller uses anti-grav modules also known as gravitic drive as the TL9 maneuver drive replaced by thruster plates above TL 9. The ship AG modules are much more powerful versions of vehicle AG mods. AG depends on gravitons and limits travel within gravity wells, the more powerful the further a vehicle can be from world. This is why non-ships can't venture much beyond orbit.

Low tech spacecraft use agrav for M-drives, but they seem to replaced by thrusters as soon as they are available. Most spacecraft, e.g. in the ImpEnc, seems to use thrusters, not agrav, and not both.
In the design system you can easily install both if you want, but most ships do not do that.
The spacecraft agrav modules seems to be the same as TL9 "Standard Grav" modules for smaller craft.

You might want to read T5 pg. 323 How maneuver works for current insight.

Sorry, I do not have T5. Does it follow CT, MT, or TNE drive paradigm?

 

[Reynard]

"I certainly agree TNE spacecraft use contragrav, but TNE changed the M-drive completely so I don't think it says much about earlier editions. I think this discussion started with:
AnotherDilbert wrote:
CT, MT, and MgT ships don't normally use contragrav or even a-grav."

Once again, and I'll detail, MegaTraveller Referee's Manual page 65 clearly shows anti-grav units for starships. This is a very high powered version of vehicular AG found on page 66 under thrust based suspensions which also provide lift and thrust. As to Classic Traveller mentioning it, I'll have to pour through a LOT of books, supplements and the Journals for any reference. Some how I don't believe MegaTraveller just suddenly decided to make AG c as a lifting systemanon but...

MgT has been vague about what maneuver actually is or does, as it is about a lot of technological things. It doesn't say it uses AG or CG BUT it doesn't say it doesn't. That fact that so many editions before it and the concurrent T5 does acknowledge anti-grav lifters and thrust seems to balance the system in canon to anti-grav.