Do MGT Traveller ships have anti-gravity for lift?

[AnotherDilbert]

Is that possible? Sure. Does it pass the common sense test? No, not at all.

I disagree. Technology is not perfect, but limited by cost and physics.

My car is, disappointingly, not able to fly, despite the technology has been available nearly a century.

Ocean-going ships are generally quite clumsy in ports, needing tug-boats to dock, despite the technology being available.

Airliners need massive runways and finicky take-off/landing operations, despite helicopters being available.


Spacecraft having anti-grav capability would be an advantage, but it is expensive and not strictly necessary.

 

[Reynard]

To me, anti-grav and contra grav are similar concepts given slightly different descriptions and uses depending on the edition of Traveller just like various descriptions of the M-drive. One thing that always sells me on AG/CG as standard for Traveller ships are the descriptions and illustrations of Downports. Landing strips are not a regular features but we see landing pads in abundance and that suggests to me ships and small craft normally use VTOL Wilderness landings are part and parcel to Traveller too and there are very few convenient long, flat landing features on many worlds.

 

[AnotherDilbert]

To me, anti-grav and contra grav are similar concepts given slightly different descriptions and uses depending on the edition of Traveller just like various descriptions of the M-drive.

Oh, yes, very similar, just the small difference that contra-grav requires separate propulsion system.

One thing that always sells me on AG/CG as standard for Traveller ships are the descriptions and illustrations of Downports. Landing strips are not a regular features but we see landing pads in abundance and that suggests to me ships and small craft normally use VTOL Wilderness landings are part and parcel to Traveller too and there are very few convenient long, flat landing features on many worlds.

SSOM describes how ships with only M-drive do a vertical landings, no anti-grav required. (It's even described as canon here: http://wiki.travellerrpg.com/MegaTraveller)


If you like anti-grav starships that will of course work fine, I just do not find it necessary (or implied by the setting).

 

[phavoc]

Yes, but the shuttle could at least glide back down to earth (which is what the wings were designed to help it do). Granted though it probably wouldn't be able to take off so well.

And this gets worse of course for gas giants. The larger GGs have gravities of over 2G, and ships would be screaming in at ridiculous velocities unless they're fighting that pull. It makes me wonder if the GGs that people generally prefer to refuel at are actually the Uranus/Neptune types or smaller, because their drives might be able to handle them better.

True. The wings of the shuttle do help slow it's fall from orbit. When it deorbits and is in the atmosphere, it does a series of braking maneuvers to slow down it's speed from Mach 25+ over the Pacific. It then continues it's gliding descent to Edwards or Kennedy for landing. But unlike a Traveller craft, it really is gliding down. It's rockets are of no use, nor are it's thrusters while it's in atmosphere. For control it is using it's aircraft components (rudder, flaps, etc). The wings just help get the flying brick down safely, able to land under control instead of plopping down rather violently. I suppose, in theory, with enough runway space and thrust it would be able to take off like a plane, though that would be a LOT of runway.

Ok, under the 1st edition of CT (77) the 1g freetrader could not lift from a size 7 world or larger without help. The 2nd edition of CT (80) was missing that rule. Though if you look at the Using Striker with Traveller section of the Striker rules it stated that a ship's g rating need to be higher than the planet's gravity provide close support (i.e. anything other than orbital bombardment).

Also note a lot of early articles assumed that Starports had lift pad to help starships off of planets. And one iteration of the Launch had 1g thrust and 1g lift installed which would morph into 2g of thrust...

So within CT both views have been represented.

Now T5 has Lifters which counteract gravity and provide a miniscule amount of thrust.

Here is another thought, think of the visuals, with just the thrust model most of your vtol craft can have the great swinging thrust engines keeping them in the air. Where with the Contragravity model you can have all those aerial constructs just floating there (think Airboats and the like).

I think I am mostly the latter.

Spacecraft along the lines of the tug wnbc illustrated, or the Serenity from Firefly would fit within the VTOL concept, and I would have no issue with them. In CT there were some downport illustrations that showed large repulsor grids that helped the larger craft safely take off/land. But the concept still required them to be able get off the ground on their own in some way. There were no taxi ways or runways for spacecraft. Though there was no specific text indicating that, it was more inferred from the illustration and descriptions. The idea, I believe, being that the Free Trader was underpowered for operations on larger worlds and needed assistance.

I assume their aerodynamic lift is not enough, without knowing anything about it. The original LBB2 Liner is unstreamlined, hence the illustrations.

We can start like a rocket, the M-drive can be overdriven for short periods of time (MT, MgT).

That would still imply a tail sitter taking off like a rocket. With onboard gravity systems the passengers would not notice that the ship was not perpendicular to the ground, so that's entirely possible. However to be practical it would really need a launch cradle (again also entirely possible - many sci-fi visions have something similar). Using the ships thrusters to provide lift seems to me to make them quite overpowering and quite possibly as powerful as the main engines. In such a scenario it would make more sense to have your engines on gimbals so that they could provide both lift AND thrust. I haven't seen any Traveller illustrations of ships of that type. The Serenity from Firefly had a main engine in the rear, but the engines on the side were positioned and sized to make this a reasonable argument.

Anti-grav systems are not cheap. In MT a anti-grav suspension would cost in the order of MCr 5 use 200 MW and several dT, the increased PP would take a few more MCr and dT. If you do not mind that you MCr 37 Free Trader becomes a MCr 47 Free Trader with 10% less cargo, killing your profit margin, you are welcome to do it, but it will not be standard.

A ground car costs around kCr 3, an air/raft costs around kCr 300, air/rafts will not replace ground cars anytime soon. Air/rafts will replace helicopters. Even on HiTech worlds ordinary people make in the order of kCr 10 / year, they cannot afford grav vehicles.

Edit: I should use MgT2 prices: Ground car kCr 6.5, Air/raft kCr 250, still too expensive.

No, they aren't. But neither are starships either. I think this is where the design rules were not properly fleshed out to include this idea in the base designs. Which brings up an interesting point. When you see all the small craft that are out there, there have been many images where you see modular cutters and other similar craft that have absolutely no inherent aerodynamic lift capability, nor any obvious outsized thrusters. Yet these craft are not prohibited from flying and landing on planets. In fact the modular cutter has a number of modules specifically designed to be landed and released on a planet. The cutter has no specific anti-gravity system spelled out. So either it (and by default all similar ships) has an inherent anti-gravity capability, or it doesn't. And if it doesn't then it and all previous versions of the modular cutter have been "broken" from a design perspective.

 

[Reynard]

"SSOM describes how ships with only M-drive do a vertical landings, no anti-grav required."

No AG required because the Thruster Plate system acts as a form of AG for vessels 20 tons and greater. Actual AG systems are use below that. Except for the Mercenary Cruiser, the majority of landable ship designs, by their illustrations, must first land on their tails to utilize full thruster plate power then literally tip over onto their belly to finish landing because they are not structurally able to 'sit' on the aft section. Because the thruster plate can direct 25% thrust 90 degrees laterally (including dorsal and ventral) they can make typical belly landings but with far less control. It's complicated which is why reinstating anti- or contra gravity units (lifters) on ships simplifies things and MegaTraveller was never simple.

 

[phavoc]

Is that possible? Sure. Does it pass the common sense test? No, not at all.

I disagree. Technology is not perfect, but limited by cost and physics.

My car is, disappointingly, not able to fly, despite the technology has been available nearly a century.

Ocean-going ships are generally quite clumsy in ports, needing tug-boats to dock, despite the technology being available.

Airliners need massive runways and finicky take-off/landing operations, despite helicopters being available.


Spacecraft having anti-grav capability would be an advantage, but it is expensive and not strictly necessary.

I've seen a cruise ship do a 360 maneuver in front of me before docking on it's own. Thruster pods for ships are the norm now for cruise liners, and they are present on other ships as well. There proper term is azimuth thruster. There are pros and cons to thrusters, and while some military ships have smaller thruster pods for docking and such they have maintained the normal propellor's primarily (AFAIK) due to the nature of pods and turning and speed loss. At least that's what I've read. I only play at being a naval engineer.

You car COULD be flying. But it's not because (a) flying anything is much more expensive than a Toyota Corolla, (b) the aviation authorities in most countries are very hesitant to license and approve flying cars, and (c) our infrastructure hasn't adapted to it. There are new designs out there with fully electric propulsion that fly like helicopters, but don't have the same need for piloting skills or the very expensive cost for turbine helo's. But they aren't approved... yet. One can only hope that we will finally start allowing this if only to see how stupid people can be with them.

Yes, airliners do need runways. But Traveller starships do not? See, that's the problem with the argument against spacecraft and starships not having contragravity systems. If they do not, then they have to taxi or be towed to get to their loading/unloading areas. I've never seen or read where a starship landing gear is wheeled. Everything points toward them having claws or flat feet. That implies they do NOT get moved once they land, unless they hover to move.

I can tell you aren't a fan of the idea, but everything out there points to this concept being the default. Some of your explanations are reasonable, yet the argument FOR it being the case seems far more reasonable and realistic than any other. I mentioned in my previous reply that most of the small craft (at least those that are barrel shaped) would be unable to ever land on a planet, yet their functions indicate otherwise. I would be interested in hearing a defense of their configurations and no stated prohibitions against landing from you.

 

[fusor]

Jupiter has an escape velocity of ~60 km/s, achievable in 3 h with 1G. A fuel skimming pass would, I imagine, be a gravitational slingshot through the extreme upper edge of the GGs atmosphere. You are not trying to land or slowly drifting around in the GG.

Erm, yes you are. A gravitational slingshot through the upper edge of the GG's atmosphere with open scoops would destroy the ship (remember what happened to the shuttle Columbia? That would happen to the ship). You don't want superheated atmosphere smashing into the insides of your ship at those velocities at all. You'd want to do it slowly, possibly just hovering in the atmosphere and drawing in the gas around the ship.

Or just go for the easier option and land on an icy moon and start breaking down the hydrocarbons and water.

 

[wbnc]

Jupiter has an escape velocity of ~60 km/s, achievable in 3 h with 1G. A fuel skimming pass would, I imagine, be a gravitational slingshot through the extreme upper edge of the GGs atmosphere. You are not trying to land or slowly drifting around in the GG.

Erm, yes you are. A gravitational slingshot through the upper edge of the GG's atmosphere with open scoops would destroy the ship (remember what happened to the shuttle Columbia? That would happen to the ship). You don't want superheated atmosphere smashing into the insides of your ship at those velocities at all. You'd want to do it slowly, possibly just hovering in the atmosphere and drawing in the gas around the ship.

Or just go for the easier option and land on an icy moon and start breaking down the hydrocarbons and water.

The Columbia burned because those gases got where they weren't supposed to be.

the trick would be to find an altitude where the gasses were thick enough to scoop, but not so thick they cause unacceptable frictional heating. then accelerate just enough to overcome the drag trying to slow your craft and force it lower into the atmosphere. really very simple...as simple as any process involving every law of motion, gravity, and thermodynamics can be...

if you get the numbers right it's perfectly safe.just pray you don't lose a primary buffer panel while skimming...

 

[rust2]

Do you consider Traveller starships to have built-in anti-gravity/contragravity capabilities such that by using their antigravity alone they can ascend to orbit or descend from orbit without using their main drives ?

Yes. The starport examples in the Mongoose Traveller Starports supplement are obviously designed for VTOL vehicles, with landing pads like those for helicopters. Looking at the configuration of most Traveller starships able to land on planets and remembering that form goes with function, for me the existence and common use of antigrav/contragrav is the most plausible explanation.

 

[fusor]

The Columbia burned because those gases got where they weren't supposed to be.

Sure, but that doesn't change the fact that the stresses of re-entry (especially when you're coming in at 40-50 km/s) are ridiculous. You can't barrel in there, "open up the scoops" and not expect things to break apart (even more so when your ship isn't even a streamlined airframe).

Fuel scooping has to be slow and gentle. It's a myth that you can basically scoop while aerobraking.

 

[phavoc]

The Columbia burned because those gases got where they weren't supposed to be.

the trick would be to find an altitude where the gasses were thick enough to scoop, but not so thick they cause unacceptable frictional heating. then accelerate just enough to overcome the drag trying to slow your craft and force it lower into the atmosphere. really very simple...as simple as any process involving every law of motion, gravity, and thermodynamics can be...

if you get the numbers right it's perfectly safe.just pray you don't lose a primary buffer panel while skimming...

I gotta agree with Fusor on this one. For Columbia the issue was the inside of the wings was incapable of taking the heat that the outside hull was. The inside of a starship would be no different. The flow of the gas coming through the fuel scoops would be at tremendous pressure - the faster you are going the more force of the gases. So the piping you are going to have means they would have to take a lot of pressure - potentially more so than your outer hull. Then you are going to have all that pressure coming into your fuel tank and going... where exactly? You can see for yourself how this would be self-defeating by putting a glass underneath a tap and opening up full blast. Some of that water will come splashing out because of the force. A fuel tank will be even worse because the pressure will force the gases back out, so you'd have to have series of baffles that prevent this. Which means your internal tanks are going to have tremendous force applied to them just to stop from splitting open.

It can probably all be engineered to work, however it's going to cost a lot in terms of mass and credits. To make it all work with a minimum of handwaving, it's better to keep the speed of the vessel down to a few hundred KPH AT MOST. This makes the idea more reasonable and the assumptions behind the engineering of the innards more reasonable as well.

 

[wbnc]

I'll get back to the skimming issue....

I think we have at east some indicator shis do have contra grav drives hidden in the advantages/disadvantages section.

High Guard Pg 49

Limited Range: This manoeuvre drive only functions within the 100 diameter limit

Orbital Range: This manoeuvre drive only functions when the ship is within Short range (up to 1,250 km) of a planetary body. Orbital range requires two Disadvantages.

A reaction based system like plasma rockets would not be affected by the proximity to a planet. that would only be a factor is a ship is using gravitic systems. So it seems to me that a standard M-drive uses gravitics, or at least includes them, and is capable of generating thrust without a naturally occurring gravity well.

 

[AnotherDilbert]

Erm, yes you are. A gravitational slingshot through the upper edge of the GG's atmosphere with open scoops would destroy the ship (remember what happened to the shuttle Columbia? That would happen to the ship). You don't want superheated atmosphere smashing into the insides of your ship at those velocities at all. You'd want to do it slowly, possibly just hovering in the atmosphere and drawing in the gas around the ship.

Or just go for the easier option and land on an icy moon and start breaking down the hydrocarbons and water.

I told you I did not know what I was talking about...

My basic assumption was that we can choose the density of the hydrogen atmosphere by choosing the altitude at which we are skimming. 40 km/s is a rather absurd speed, but I hoped that by choosing a very low density we could still get a reasonable flow over the hull and into the scopes. Perhaps such a low density will yield insufficient fuel?

An icy moon or asteroid is perhaps better, but probably takes more time?

 

[fusor]

My basic assumption was that we can choose the density of the hydrogen atmosphere by choosing the altitude at which we are skimming. 40 km/s is a rather absurd speed, but I hoped that by choosing a very low density we could still get a reasonable flow over the hull and into the scopes. Perhaps such a low density will yield insufficient fuel?

40 km/s may sound absurd, but it's about how fast the Galileo orbiter was going when it was deorbited into Jupiter's atmosphere (I think it was going more like 50 km/s actually). And that pretty much just 'fell in', it just picked up that speed from Jupiter's gravity as it dove in on its final orbit.

An icy moon or asteroid is perhaps better, but probably takes more time?

"More time" is probably infinitely preferable over "very likely ship destruction" and "wrestling with a huge gravity well". And most gas giants have icy moons anyway.

 

[AnotherDilbert]

I've seen a cruise ship do a 360 ...

You car COULD be flying. ...

Yes, airliners do need runways...

My point, that you chose to creatively misunderstand, is simple: Just because a technology is available and beneficial does not mean that it is standard.

I can tell you aren't a fan of the idea, but everything out there points to this concept being the default. Some of your explanations are reasonable, yet the argument FOR it being the case seems far more reasonable and realistic than any other. I mentioned in my previous reply that most of the small craft (at least those that are barrel shaped) would be unable to ever land on a planet, yet their functions indicate otherwise. I would be interested in hearing a defense of their configurations and no stated prohibitions against landing from you.

Reasonable is in the eye of the beholder.

Everything does not point to anti-grav being standard. Most written canon (CT, MT, and some MgT) says spacecraft does not have anti-grav as standard, e.g. MgT1 HG p66, and SSOM explains how that would work. I hear you say it would be better if they had, and hang the cost, and I find that not enough to override canon.

 

[wbnc]

[
Everything does not point to anti-grav being standard. Most written canon (CT, MT, and some MgT) says spacecraft does not have anti-grav as standard, e.g. MgT1 HG p66, and SSOM explains how that would work. I hear you say it would be better if they had, and hang the cost, and I find that not enough to override canon.

High Guard Pg 49

Limited Range: This manoeuvre drive only functions within the 100 diameter limit

Orbital Range: This manoeuvre drive only functions when the ship is within Short range (up to 1,250 km) of a planetary body. Orbital range requires two Disadvantages.

A reaction based system like plasma rockets would not be affected by the proximity to a planet. that would only be a factor is a ship is using gravitic systems. So it seems to me that a standard M-drive uses gravitics, or at least includes them, and is capable of generating thrust without a naturally occurring gravity well.

 

[AnotherDilbert]

That would still imply a tail sitter taking off like a rocket.

Or M-drives with thrust vectoring, as described in SSOM.

I think this is where the design rules were not properly fleshed out to include this idea in the base designs.

I would certainly welcome anti-grav drive that could be installed together with or instead of M-drives.

 

[AnotherDilbert]

High Guard Pg 49

Limited Range: This manoeuvre drive only functions within the 100 diameter limit

Orbital Range: This manoeuvre drive only functions when the ship is within Short range (up to 1,250 km) of a planetary body. Orbital range requires two Disadvantages.

A reaction based system like plasma rockets would not be affected by the proximity to a planet. that would only be a factor is a ship is using gravitic systems. So it seems to me that a standard M-drive uses gravitics, or at least includes them, and is capable of generating thrust without a naturally occurring gravity well.

According to ye olden books (MT, TNE) M-drives do not use reaction mass and is independent of the local gravity field. If it only works in a gravity field it is not an M-drive, but rather an anti-grav drive.

To me this indicates that we could possibly use say a budget M-1 drive with Orbital Range and Energy Efficient to simulate an anti-grav drive (to be used in addition to an M-drive). It would even be small and cheap.

If it's that small and cheap you might even convince me that it should be standard equipment on spacecraft...

 

[-Daniel-]

I think this is where the design rules were not properly fleshed out to include this idea in the base designs.

I would certainly welcome anti-grav drive that could be installed together with or instead of M-drives.

I would love a clear answer being given within the rulebook rather than this unclear offering of hints and assumptions. Now that is not to say you guys are wrong, rather I respect the effort you all put in to share quotes and sources. I just think this is an important enough question that it deserves a clear and direct answer either way. :mrgreen:

 

[phavoc]

My point, that you chose to creatively misunderstand, is simple: Just because a technology is available and beneficial does not mean that it is standard.

For the record I wasn't trying to be sarcastic or anything. As for what "standard" is, well, that's an interesting question without a clear answer, for the most part at least. Flying cars COULD certainly be a standard today, but society tends to take things that have the potential to fall out of the sky pretty conservatively. The technology has been around for decades. However it's also tech for the rich, so the audience is limited, thus the "standard" remains elusive.

Reasonable is in the eye of the beholder.

Everything does not point to anti-grav being standard. Most written canon (CT, MT, and some MgT) says spacecraft does not have anti-grav as standard, e.g. MgT1 HG p66, and SSOM explains how that would work. I hear you say it would be better if they had, and hang the cost, and I find that not enough to override canon.

I fundamentally agree here. Which is why I started the thread in the first place.

The issue here is that the rules simply do NOT state it, either way, whether or not contragravity is standard equipment for spacecraft. I have presented a number of reasons why it SHOULD be considered thus. You've presented some reasons why not. However, the statement of "not enough to override canon." is an unfair dismissal of the arguments that run counter to yours. We all know that the rules of Traveller have large gaps in them, in most all of the versions (except perhaps GURPS - they did a fantastic job on their ruleset - in my opinion).

To wit, we know contragravity exists for small vehicles. We know that small craft, such as the modular cutter, can never generate any lift due to their shape, we know that the modular cutter (Across many canon rule sets) has the ability to land on a planet to drop off modules. And we know from the ships description that nowhere does it categorically state that the ship is incapable of operating in a planetary atmosphere. While this is a single example, it's an example of how the rules do not discuss this at all.

We also have seen from other canon sources that the idea is starships are able to land in extremely small areas, thus they need to operate as closely to a VTOL-like manner as possible. Your argument has been that since it is NOT stated that starships have contragravity, it must not be canon. However since the design sequence doesn't say what all you get with your hull, it's not unfair to state that starships have that built into the cost. Nowhere in the rules does it state that a starship has superconductors, or, heck, even bathrooms for that matter. But we've seen them on the ship diagrams (canon diagrams to be exact), so we all assume that bathrooms are paid for as part of the cost of a stateroom. That's no different of an inference than is being made here.

I'm not opposed to the idea that somehow I'm wrong. And if you want to dismiss my argument outright, that is your right. However I haven't seen a convincing argument to state they don't yet. Alternatives, yes. And some reasonable ones. But the sum total of the evidence seems to point in the opposite direction.

At least that's my opinion.