Ships Drives

[phavoc]

Rather than continue disrupting WNBC's free trader thread with this, I thought it would be polite to split it off.

So there seems to be two sides to this discussion. One side posits that MGT Maneuver drives can expend thrust in any direction, thus they may be located in the center or anywhere in the ship and output thrust in any direction, with or without exposure to space. The argument for this view is that it's not explicitly defined, one way or the other, therefore this idea remains valid.

The other side says nyet to that idea. That maneuver drives operate the same in all the versions of Traveller - in that they exert a force or expel energy in one direction, thus a ship is pushed in the other. Which is why 99.99% of all starship deck plans and illustrations show them in the rear of the ship, as well as the travel charts showing charts that dictate a ship must rotate 180 degrees and decelerate towards it's destination. This fits within the ideas of physics today and has remained a constant concept through every version of Traveller - stated or implied.

So which version do YOU believe? Why, or why not?

 

[wbnc]

I mentioned it in the other thread, by the way thanks for the split off post

This touches on two issues, artistic and practical.

artistically
Most people look at a ship and their brain goes.."Umm where are the engines?"/"Which way is it supposed to be pointing?" The rocket nozzles give their brain a point to lock onto and go.."OH! thats the rear!" sort of along the same lines as why starships have visable bridge structures and engines at one end. Most people get lost without them and the design doesn't "look right"

However, there are some folks that look at something and go"Why the hell is that there?" or "Oh good lord that makes no sense"

A good design finds that middle ground where both sides are able to go..Okay that looks good....Still looking for that balance point myself.

Traveller ships artistically are still using a set of desing principles from early sci-fi when very few people understood the principles involved. More modern consumers have a bit more critical eye. Lets face it few old ships can stand up to close scrutiny from anyone who has an inkling of how a ship would owrk. My favorite example would be the fat trader which would tumble like a drunken duck in a Typhoon if it didn't have garvitics. to short, too fat, wings are all wrong.... BUT it looks enough like a shuttle or airplane to pass for practical at a casual glance....and for the love of the Infinite verse, thank goodness the Plankwell, and AHL never have to get in the same postal code as a gravity well, they'd some apart under the stress loading.

Now one note is that artistic and practical can cohabitate elegantly. if it looks right it flies right..I mean look at some of Burt Rutan's aircraft the are almost flying sculpture. Better yet look at the old Spitfire. That thing is was not built to be pretty, It was meant to e a weapon... but the laws of aerodynamics and the way they were applied resulted in a very lovely shape...



Then we get to the practical side of things..

As I understand it traveller gravitic drive is not a reactionless drive at all, but the name just hangs around cause we're used to it.Traveller uses the idea of thrust generation by use of exotic particles instead of manipulating the local gravity field/Timespace. That method almost requires some form of directional generation to work properly. The crudest example I can think of are the repulsor "rockets" from the Ironman movies..yes I know it's a lousy example( too much Fi, not enough sci). but they drives generate thrust in one direction and it is focused and directed as needed.

The thrust is generated electrically/electronically instead of chemically, controlled by varying the thrust of individual plates.The visual feature of thruster nozles is a hodover from early sci-fi. It's not totally impractical but it is not properly explained. It's not bad, or lazy, after all
I like to use the idea from Starship Operators manual that plates only generate full "thrust" in one direction which falls off rapidly as you move away from that direction. Yess a plate can generate 360x360 thrust but it is more powerful in one primary direction.

In theory you can arrange plates in a lot of configurations to get varying results. A spherical or dome shaped thruster gives very flexible wide area of effect thrust. while a cone, generates directional thrust, with the ability to electronically steer the thrust. A flat plate gives very powerful thrust in one direction but limited ability to generate the same power away from its main axis of thrust.So on a ship you would likely see domes, cones, and plates placed in various positions to achieve both brute force and precision thrust.

artistically those various types of thrusters are great for adding interesting doodads, and diddlybops all around a ship..within reason. adding a few gives a desing some thing to catch the eye, or make a critical observer go Hmmmm.."What's That Do?"

 

[Condottiere]

Pusher propulsion would be the classic, which is why drives face backwards.

Field effect allows more latitude.

And the field effect could be optimized in a specific direction, permanently, or by flipping magnets during operation, ad hoc.

 

[phavoc]

I don't disagree with that idea at all (spreading thruster plates around). But, at least as far as I can tell, maneuver drives in Traveller have all pretty much operated on the idfea of 'pushing' out or against the ship to provide forward thrust momentum. There's no reason why you cannot have engines in all planes of a vessel - however by doing so you would drive up your costs and maintenance by now having to pay for all those extra engines. So it makes practical sense to not do so.

All versions of Traveller (including MGT2) use Newtonian movement and the concept of inertia. The idea of reactionless drives doesn't fit within the rest of the engineering concepts the game lays out. I could see locating your powerplant in the middle of the ship to provide maximum protection, and even the jump drive, which forms a jump bubble around the vessel. But usually the idea is you put your engineering equipment in the same location to make it easier to monitor and repair. I'm a huge fan of form following function.

Field effect allows more latitude.

Agreed. Which follows that the anti-grav fields used by vehicles and ships to lift out of a gravity well work the way they do, and become less efficient, and eventually useless, outside of a gravity well. Which is why maneuver drives are still required.

 

[fusor]

Most people look at a ship and their brain goes.."Umm where are the engines?"/"Which way is it supposed to be pointing?" The rocket nozzles give their brain a point to lock onto and go.."OH! thats the rear!" sort of along the same lines as why starships have visable bridge structures and engines at one end. Most people get lost without them and the design doesn't "look right"

Two words: "Flying saucers" . Those usually aren't depicted with engine nozzles and a "front" or "back", and people don't seem to have trouble with that. Though granted, if the drive in Traveller really doesn't have to push in a specific direction then one would expect the ships to look more symmetrical like flying saucers (it doesn't have to, but it can look like that, at least).

TNE's FF&S (pg73) says this about Thruster Plates :

Maneuver drives in previous editions of Traveller were explained as related to the same body of theoretical physics which allowed artificial gravity and damper fields, which is to say manipulation of gravitational force and the strong nuclear force. Artificial gravity was defined as a force which could either push or pull and which acted on the gravitational field of a mass. Clearly, this would not be an efficient means of travel outside of a gravity well, and so a further advance was postulated which allowed the force generated by the drive to push on the actual thruster plates of the ship itself, propelling it through space and achieving a true reaction less drive.

From that, and given that Plates need to be installed on the hull, it really sounds like the plates are mounted in the opposite direction to where the ship wants to move (i.e. they're mounted on the "back" of the ship to move the ship in the "forward" direction), because the drive pushes against the plates to move. Of course, you'd probably also have a few thruster plates mounted elsewhere on the cardinal axes of the ship so it can turn, move up or down, etc. I guess the drive itself could be located anywhere in the ship - so long as it's connected to the thruster plates (which do have to be mounted in specific locations) the ship can move in the corresponding direction.

In short, according to TNE at least, ships should look "normal" with an "engine" at the back (actually a load of thruster plates against which the ship is pushing).

 

[Condottiere]

You can allow all solutions, tempered by cost(s).

 

[rust2]

So which version do YOU believe? Why, or why not?

With these two options to choose from I would tend to the second one, because the first option seems to contradict the published ship designs with their drives at the ship's rear.

However, I actually find both options highly questionable. The Traveller maneuver drive is volume based, not mass based. To accelerate a dton of uranium requires
the same "thrust" as to accelerate a dton of empty space. In my view this demonstrates that any attempt to explain Traveller's maneuver drive with (fictional) physics instead of game requirements does not really make much sense.

 

[phavoc]

[Two words: "Flying saucers" . Those usually aren't depicted with engine nozzles and a "front" or "back", and people don't seem to have trouble with that. Though granted, if the drive in Traveller really doesn't have to push in a specific direction then one would expect the ships to look more symmetrical like flying saucers (it doesn't have to, but it can look like that, at least).

Also present on the cover of a number of ELO's albums.

In short, according to TNE at least, ships should look "normal" with an "engine" at the back (actually a load of thruster plates against which the ship is pushing).

Yes, the HEPLar plates. But they essentially worked the same way as conventional reaction engine.

With these two options to choose from I would tend to the second one, because the first option seems to contradict the published ship designs with their drives at the ship's rear.

However, I actually find both options highly questionable. The Traveller maneuver drive is volume based, not mass based. To accelerate a dton of uranium requires the same "thrust" as to accelerate a dton of empty space. In my view this demonstrates that any attempt to explain Traveller's maneuver drive with (fictional) physics instead of game requirements does not really make much sense.

Yes, I agree with that. How a multi-million ton starship is able to have the same acceleration profile as a 10 ton fighter seems questionable to me. My understanding of the anti-gravity capabilities a ship might have is that it can offset weight, but the objects mass stays the same. Thus the amount of energy to move it remains the same regardless of where it is. GURPS attempted to shoehorn mass into the equation, and I believe MT and the first HG had the concept of agility, based upon the size of your ship and your powerplant size.

With the inclusion of energy points it seemed to me like a natural opportunity to re-introduce the agility rating of a ship, which would allow you to put a more powerful plant in your vessel to give it greater agility, or the ability to fire more energy-hungry weaponry.

 

[fusor]

However, I actually find both options highly questionable. The Traveller maneuver drive is volume based, not mass based. To accelerate a dton of uranium requires
the same "thrust" as to accelerate a dton of empty space.

In TNE the M-drives were mass-based (pg69 of FF&S)... quite why they refuse to use mass in other editions is beyond me.

 

[fusor]

Yes, the HEPLar plates. But they essentially worked the same way as conventional reaction engine.

HEPLar was the default (reaction) engine design assumed for TNE, and was different from previous editions - I'm not talking about that here (that's got a more complex design sequence).

I'm talking specifically about Thruster Plates, which were presented in FF&S as an "alternate M-Drive technology" but are specifically supposed to be the same reactionless tech that was used for M-Drives in previous versions of Traveller.

 

[wbnc]

Two words: "Flying saucers" . Those usually aren't depicted with engine nozzles and a "front" or "back", and people don't seem to have trouble with that. Though granted, if the drive in Traveller really doesn't have to push in a specific direction then one would expect the ships to look more symmetrical like flying saucers (it doesn't have to, but it can look like that, at least).

TNE's FF&S (pg73) says this about Thruster Plates :

Maneuver drives in previous editions of Traveller were explained as related to the same body of theoretical physics which allowed artificial gravity and damper fields, which is to say manipulation of gravitational force and the strong nuclear force. Artificial gravity was defined as a force which could either push or pull and which acted on the gravitational field of a mass. Clearly, this would not be an efficient means of travel outside of a gravity well, and so a further advance was postulated which allowed the force generated by the drive to push on the actual thruster plates of the ship itself, propelling it through space and achieving a true reaction less drive.

From that, and given that Plates need to be installed on the hull, it really sounds like the plates are mounted in the opposite direction to where the ship wants to move (i.e. they're mounted on the "back" of the ship to move the ship in the "forward" direction), because the drive pushes against the plates to move. Of course, you'd probably also have a few thruster plates mounted elsewhere on the cardinal axes of the ship so it can turn, move up or down, etc. I guess the drive itself could be located anywhere in the ship - so long as it's connected to the thruster plates (which do have to be mounted in specific locations) the ship can move in the corresponding direction.

In short, according to TNE at least, ships should look "normal" with an "engine" at the back (actually a load of thruster plates against which the ship is pushing).

Yes UFOs break that rule..So they look ALIEN the look and behave in ways the human mind is not accustomed to. No front, no back, no obvious signs of how they are being moved about.They are readily believable within the fraemwork of a super advanced technology.

You can allow all solutions, tempered by cost(s).

That should be encoded in every engineering journal in existence. If cost, either monetary resource expenditure or technical capabilities is higher than is practical it is not gonna happen.

 

[Reynard]

Going through my extensive collection I see several references to the nature of maneuver drives.

Classic Traveller in both Starships and High Guard lack descriptive detail for maneuver drive until you find the one reference in Starships page 22 (Starship Combat) which states, "Ships maneuver using reaction drives, referred to as M-drive or maneuver drive." There you have it an why ships since the beginning of Traveller have nozzles. I then cross referenced Mayday for possible information. The vector system game mechanic does suggest lots of old fashion crude reaction thrusting and maneuvering.

That should be the end of it until you read MegaTraveller. Here, maneuver became manipulation of sub-atomic forces to push against using thruster plates which don't produce a reaction mass. Page 56 of the Referee's Manual states "This new, artificially generated force pushes against a vessel's 'thruster plates' themselves, which make true reactionless thrusters a reality for starship-sized vessels." So Traveller went reactionless after Classic. They also differentiate between grav modules and thruster technology. MegaTraveller Starship Operator's Manual has an excellent section greatly detailing how maneuver works including a illustration showing the plate is stationary but manipulation of power on the plate determines thrust. Full power towards the aft rapidly dropping off to 25% at 90 degrees (including vertically) and 10% when applied fore. There's also this, "Although the plates can be located anywhere on the hull and still function, convention calls for them to be located in the aft section of the ship."

Fire, Fusion and Steel (TNE 1994) introduces the HEPlar drive as the standard maneuver drive and states hydrogen is used as reaction mass in the form of super-heated plasma. It seems they wanted a sense of realism, more hard science but is played loose to achieve satisfactory fuel efficiency for game purposes. Problem is these mothers don't appear until TL 10 otherwise starships use a hybrid of air-breather/rocket (AZHRAE) or actual rockets. Then there's mention that these systems rely on Contra Gravity Lifters to assist the ship into orbit or gravity will seriously eat into thrust efficiency. Thruster plates are actually an alternative drive system. It restates this system manipulates gravity and strong nuclear forces that either push or pull against the gravity of a mass. The generated force pushes on the actual thruster plate. Here though, they assume thruster tech only arrives at TL 11.

Marc Miller's Fire, Fusion and Steel (1997) also states the use of reaction drives as in TNE version below TL 12 after which reactionless thruster plates are the norm. Contra Grav drive here actually provide some thrust whereas TNE CGs are gravity neutralizers only. This explains the image concepts of ships landing and maneuvering like a vertical take off and landing craft.

I can't comment on GURP Traveller as I never had it.

Mongoose Traveller High Guard makes it clear maneuver is a gravitic drive compared to the reaction drive. That seems to hint gravitic isn't using reaction mass.

Finally, Traveller 5 separates interplanetary drives as Lifters, Gravitic and Maneuver with a nod to other alternatives and are all gravity based. M-drive push against gravity wells to produce vector movement (Sounds like being in a pool of water and pushing off the wall to move.)and are effective to a 1000D limit, G-drives are good out to 10D and Lifters are optimal to 1D. Illustration in the maneuver section has it against an internal hull but no reason why.

 

[AnotherDilbert]

Classic Traveller in both Starships and High Guard lack descriptive detail for maneuver drive until you find the one reference in Starships page 22 (Starship Combat) which states, "Ships maneuver using reaction drives, referred to as M-drive or maneuver drive."

That must be LBB2'77, because LBB2'81 does not say that.
HG'80 says:

Fuel consumption for maneuver drives is inconsequential, and is assumed to be part of the power plant consumption, regardless of the degree of maneuver undertaken.

Hence I have always assumed reactionless drives.

So reactionless drives came in the middle of CT, but the exhaust nozzles were already firmly entrenched in the starship illustrations.

 

[Tenacious-Techhunter]

I prefer whichever option violates the least total game material, physics included, and pictures of ships excluded, because artists...

No RCS system, or maneuvering system separate from the drive providing main thrust, is ever specified, although clearly, that function must be performed somehow, because ships can turn. Sometimes, this is even represented with an Agility number in some editions, but sometimes not. Ships also can slow down without turning... and at the same rate, no less. The only thing to conclude from these scant few facts provided by the game rules is that ships can thrust omnidirectionally. This conclusion violates the least game mechanics, and is most consistent with physics, given the game rules as a constraint.

Of course, this is still crap. In order for this to work with the minimum violation of physics, you would need several thruster modules distributed around the furthest corners of the ship, so as to provide leverage for turning. But, instead, the rules say it’s O.K. to just lump it into one great big “M-Drive”, in spite of that providing no means at all for turning the craft.

If “Drive Plates” were a legitimate thing, we would see them mounted in domes and frustrums all over the ships, as often seen in wbnc’s drawings, and the rules would advise the players to distribute them around the skin of the hull in at least 4, and more often 5 or 6, different places, by way of the deck plan. But nope, none of that!

Within the canon, this entire subject is drowning in hogwash! Will a legitimate drive mechanic please step up???

I don't disagree with that idea at all (spreading thruster plates around). But, at least as far as I can tell, maneuver drives in Traveller have all pretty much operated on the idfea of 'pushing' out or against the ship to provide forward thrust momentum. There's no reason why you cannot have engines in all planes of a vessel - however by doing so you would drive up your costs and maintenance by now having to pay for all those extra engines. So it makes practical sense to not do so.

Well, that depends a great deal on what you consider “practical”. The further out from the center of mass you put your thrusters, the better turning performance per unit of fuel you get. While the big ol’ freighters don’t need to turn too fast, anything fun needs to have its engines “in the corners”.

All versions of Traveller (including MGT2) use Newtonian movement and the concept of inertia. The idea of reactionless drives doesn't fit within the rest of the engineering concepts the game lays out. I could see locating your powerplant in the middle of the ship to provide maximum protection, and even the jump drive, which forms a jump bubble around the vessel. But usually the idea is you put your engineering equipment in the same location to make it easier to monitor and repair. I'm a huge fan of form following function.

The problem is, the only thing consistent with the unconstrained maneuverability dictated by the rules is nonsense. They painted themselves into the corner, and now they want to whitewash it with handwaves. I’d rather they stick to realism.

 

[Tenacious-Techhunter]

Another important thing to note about ship design and Maneuver Drives is, just because your ship can thrust in any direction, doesn’t mean it’s best to resort to a simplistic spherical design:

Most of the time, the ship is going to be executing a continuous forward burn, so elongate it, so the stresses all line up.
Some of the time, the ship is going to be skimming fuel, or performing atmospheric reentry, so streamline it.
Some of the time, the ship will be landed or docked somewhere with gravity, so design it to bear the weight.

All of these things lend asymmetry to a ship that otherwise performs symmetrically due to thruster placement.

 

[Condottiere]

How fast do you need to move to skim; or can you just sit there and hover it up?

 

[fusor]

No RCS system, or maneuvering system separate from the drive providing main thrust, is ever specified, although clearly, that function must be performed somehow, because ships can turn. Sometimes, this is even represented with an Agility number in some editions, but sometimes not. Ships also can slow down without turning... and at the same rate, no less. The only thing to conclude from these scant few facts provided by the game rules is that ships can thrust omnidirectionally. This conclusion violates the least game mechanics, and is most consistent with physics, given the game rules as a constraint.

Um, I just quoted text from FF&S that specifies all that (and there's more design detail in the rest of that section). Ships push against thruster plates, mount those appropriately on the ship to turn (most of them will be at the back). Later it specifies that the Thruster plates have a "thruster plate drive" that in FF&S generates 40 tonnes of thrust per cubic metre of drive volume (and require 1MW of power per cubic metre), and then that requires a portion of the surface area on the hull for the plates themselves.

That's pretty much the most detail any of the Traveller editions have provided about how thruster plates work, and while it's an alternate tech in TNE it's the standard tech in every other edition. The design details may be different but that's presumably how the 'theory' (such as it is) still works. Yes, it's unrealistic, but it's a magical reactionless drive - what else would you expect? If you're looking for realism here then you're looking in the wrong place.

 

[fusor]

How fast do you need to move to skim; or can you just sit there and hover it up?

I think you pretty much have to just sit there and hoover it up (or move very slowly, at least). If you start opening up holes in your ship while travelling at very high speed while aerobraking through the atmosphere, the ship's going to end up like the Columbia space shuttle - breaking up under the stress. The heating and drag would be ridiculous - but if you slow down and drift or float then the stresses would be vastly easier to handle.

That said it'd be a pretty slow process probably. Better to use water or methane ice (there'd be more hydrogen per cubic metre).

 

[Tenacious-Techhunter]

Um, I just quoted text from FF&S that specifies all that (and there's more design detail in the rest of that section). Ships push against thruster plates, mount those appropriately on the ship to turn (most of them will be at the back). Later it specifies that the Thruster plates have a "thruster plate drive" that in FF&S generates 40 tonnes of thrust per cubic metre of drive volume (and require 1MW of power per cubic metre), and then that requires a portion of the surface area on the hull for the plates themselves.

That's pretty much the most detail any of the Traveller editions have provided about how thruster plates work, and while it's an alternate tech in TNE it's the standard tech in every other edition. The design details may be different but that's presumably how the 'theory' (such as it is) still works. Yes, it's unrealistic, but it's a magical reactionless drive - what else would you expect? If you're looking for realism here then you're looking in the wrong place.

I disagree. I’d rather start from the Hard Science Fiction and work back up to something that’s actually usable. FF&S may provide a handwave here and there, but none of it addresses the root of the problem; justifying how ships turn and stop with things you can actually reason about.

 

[fusor]

I disagree. I’d rather start from the Hard Science Fiction and work back up to something that’s actually usable. FF&S may provide a handwave here and there, but none of it addresses the root of the problem; justifying how ships turn and stop with things you can actually reason about.

It does have reaction drives, realistic thrusters, ion drives, and fusion rockets in there too.

And you can "reason" about anything, so long as it's consistent. Thruster Plates may be unrealistic, but they're consistent. You put a bunch on the back and on the bottom of the ship, you put a much smaller number elsewhere for attitude control, stick power into them and you're done. Maybe the artists and ship designers got it wrong, but that's the best description of what has been provided by the rules. If you want to demonstrate what a ship should really look like given the constraints of the thruster plates drive setup then by all means, feel free to give it a crack. GURPS Traveller: Starships mentions that M-drive modules have a vectored reactionless thruster on them (and also mentions some other realistic options for drives too like TNE's FF&S does).

But if you're determined to toss all of that out and come up with a fully realistic system with vectors and reaction drives and realistic technologies, then you're going to be a lot happier looking for another game that does that.