Do MGT Traveller ships have anti-gravity for lift?

[fusor]

This is why I hate how Traveller defines drives and speeds. You need to know the thrust, and for that you need to know the mass (which is ignored in all but TNE). "G-rating" doesn't really help much.

I believe it's an obvious simplification. If the size of the drives are dependant on all other systems, the design system becomes iterative and fiddly. It's simpler to allow you to determine the size of the drives by hull size only.

It's a non-intuitive simplification though. TNE managed to include actual thrust and mass without being iterative, so it's quite possible to do.

 

[heron61]

This is why I hate how Traveller defines drives and speeds. You need to know the thrust, and for that you need to know the mass (which is ignored in all but TNE). "G-rating" doesn't really help much.

That depends - m-drives are reactionless, and given the obvious physics failure wrt reactionless drives, they might work quite differently from reaction drives. For all we know, m-drives move a bubble of space of X dtons at an acceleration of up to Y Gs, and the mass of that bubble is not relevant or not relevant so long as it's not absurdly high (ie not normal matter).

OTOH, if you want to make m-drive somewhat less physics-breaking, then my personal favorite is to have them be drive that convert hydrogen into directed neutrinos at nearly 100% effeciency, so they are reaction drives, but have no (easily) detectable exhaust. Of course, they'd also need to have fuel, which they don't now, but not much fuel, but we'd be back to G-hours and such-like, just (roughly, IIRC) 3% of the fuel usage of Heplar drives.

 

[AnotherDilbert]

If that's the case then how does the classic Scout or Free Trader land? Traders and scouts are supposed to be land anywhere on planets to do their job. This goes against all the illustrations and concepts these ships stand for.

I have no better explanation than the unnamed third-party book I promised fusor to stop quoting.

Basically you go down balancing on the thrust from the M-Drive, straightening out in the last moment to touch down vertically.

 

[AnotherDilbert]

This is why I hate how Traveller defines drives and speeds. You need to know the thrust, and for that you need to know the mass (which is ignored in all but TNE). "G-rating" doesn't really help much.

I believe it's an obvious simplification. If the size of the drives are dependant on all other systems, the design system becomes iterative and fiddly. It's simpler to allow you to determine the size of the drives by hull size only.

It's a non-intuitive simplification though. TNE managed to include actual thrust and mass without being iterative, so it's quite possible to do.

Even TNE based drives on displacement, not mass.

Thrust requirements are abstracted by tying thrust energy requirements to hull displacement rather than craft mass. This is an obvious abstraction, but one which is necessary for ease of design. Too many variables affect ship mass throughout the design process, and tying thrust to mass would require you to continually redesign and re-design to get a workable craft.

Even so, many players thought it too complicated?

Edit: Ok, it was more complicated:

Spacecraft require (for the sake of simplicity) 10 tonnes of thrust per displacement ton to achieve an acceleration of 1G. Spacecraft with a final mass of more than 15 times (rounding fractions to the nearest whole number) their hull rate (in displacement tons) should recalculate their acceleration based on the actual thrust-to- mass ratio, dividing thrust (in tonnes) by mass (in tonnes) to determine acceleration in Gs (round fractions down).

I had forgotten that, I vaguely remembered the simplified calculation.

 

[AnotherDilbert]

OTOH, if you want to make m-drive somewhat less physics-breaking, then my personal favorite is to have them be drive that convert hydrogen into directed neutrinos at nearly 100% effeciency, so they are reaction drives, but have no (easily) detectable exhaust.

Another possibility is that the M-Drive exchanges momentum with astronomical bodies that generate the local gravity field, again making the drives not technically reactionless, but without reaction mass.

 

[phavoc]

If that's the case then how does the classic Scout or Free Trader land? Traders and scouts are supposed to be land anywhere on planets to do their job. This goes against all the illustrations and concepts these ships stand for.

I have no better explanation than the unnamed third-party book I promised fusor to stop quoting.

Basically you go down balancing on the thrust from the M-Drive, straightening out in the last moment to touch down vertically.

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

Having the ability to control gravity is a huge, huge, HUGE improvement over any other form of gravity-well maneuvers. It makes too much sense that starships are equipped with anti-gravity/contragravity (I use the terms interchangeably as I see them as the same thing). A Scout or Free Trader is going to be too heavy to provide any lift (using real-world aerodynamics. As lifting bodies they would have far too much mass to overcome with the amount of hull area available, not to mention their drag coefficients since they aren't super smooth like an airliner or fighter jet. And with a fusion plant onboard, power is not going to be an issue.

So let's explore your example above. Going "down" balancing on thrust means your craft is going to land like a common rocket ship - you wouldn't be able to be on a glide path because to change your position you'd have to stop and stand yourself on-end - now THAT would be a Bane roll for most pilots!. So that means you'd need to descend from orbit pointing engines first.

When you say "straightening out at the last moment", would require a delicate maneuver where your angle of attack would have to change to make the ship perpendicular to the ground - and you'd have to use thrusters only since your main engines are providing your lift to stay in place. That's not only inefficient, but it's dangerous too. You'd have to somehow divert your lift thrust into your thruster system because as you started to change your angle your engines would move you out of position, unless you could provide equal braking thrust to offset it.

OR, your starship could come equipped with an antigravity lift system that would allow your vessel to descend in whatever manner you choose from orbit, slow and brake above your designated landing spot, then slowly lower your vessel down to smoothly land on it's landing gear. Now that fits within all the imagery I've seen published for starports or ships on the ground at starports.

 

[fusor]

Huh. I guess I was thinking that the 10 tonnes of thrust per dt of volume was assuming a mass for that volume. Or maybe I just skipped that and just figured out the thrust to mass as if it was more than 15x the hull displacement.

Either way I think it's still better than the non-explicit way that they do it in other editions.

 

[phavoc]

OTOH, if you want to make m-drive somewhat less physics-breaking, then my personal favorite is to have them be drive that convert hydrogen into directed neutrinos at nearly 100% effeciency, so they are reaction drives, but have no (easily) detectable exhaust.

Another possibility is that the M-Drive exchanges momentum with astronomical bodies that generate the local gravity field, again making the drives not technically reactionless, but without reaction mass.

Well, the act of converting energy directly into thrust is the definition of reactionless. Had the EM drive played out, it would have been a true reactionless drive. Alas, it was not to be.

 

[AnotherDilbert]

Either way I think it's still better than the non-explicit way that they do it in other editions.

I certainly agree with you. It even makes living quarters (=empty space) on board much cheaper.

But given how many nostalgically talk about LBB2, I do not think the majority share that sentiment.

 

[AnotherDilbert]

Another possibility is that the M-Drive exchanges momentum with astronomical bodies that generate the local gravity field, again making the drives not technically reactionless, but without reaction mass.

Well, the act of converting energy directly into thrust is the definition of reactionless.

That is one definition of reactionless, another is based on Newton's Third Law.
If I gain momentum, and through the gravity field, give the nearest planet an opposite momentum, Newton's Third is satisfied and the drive is not reactionless. I think.

 

[AnotherDilbert]

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

I will come back to this, but I have to sleep...

 

[phavoc]

Another possibility is that the M-Drive exchanges momentum with astronomical bodies that generate the local gravity field, again making the drives not technically reactionless, but without reaction mass.

Well, the act of converting energy directly into thrust is the definition of reactionless.

That is one definition of reactionless, another is based on Newton's Third Law.
If I gain momentum, and through the gravity field, give the nearest planet an opposite momentum, Newton's Third is satisfied and the drive is not reactionless. I think.

Don't you mean inertialess? Traveller rules already dictate that the universe is firmly Newtonian.

 

[AnotherDilbert]

Don't you mean inertialess? Traveller rules already dictate that the universe is firmly Newtonian.

Ineartialess would mean that you violate Newton's Second, F = m × a. Basically you could skip the whole acceleration rigmarole and choose any speed want. That is even more fantastic than reactionless.

 

[fusor]

Getting back to the point of the thread...

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?

If you answer NO to the above, then please state your understanding of this and how ships are able to land at a starport or anywhere in a gravity well.

Any ship can descend from orbit without their main drives - they just fall . The question really though is what happens when the ship's drive is lower G than the surface gravity of the planet.

If they are streamlined and have wings and the planet has a thick enough atmosphere then they can just glide in and land on a runway. And I think they would be able to take off from a runway too - the lift from the wings would get them airborne and then they just need to keep pointing up and accelerating, and eventually they'll leave the atmosphere and reach orbital or escape velocity.

There are not many airless worlds that would have gravity higher than 1G (most worlds that massive would have an atmosphere) so that would be encountered much more rarely, but it could be a problem there since I think the horizontal or vertical takeoff wouldn't be an option. I think.

 

[phavoc]

Any ship can descend from orbit without their main drives - they just fall . The question really though is what happens when the ship's drive is lower G than the surface gravity of the planet.

If they are streamlined and have wings and the planet has a thick enough atmosphere then they can just glide in and land on a runway. And I think they would be able to take off from a runway too - the lift from the wings would get them airborne and then they just need to keep pointing up and accelerating, and eventually they'll leave the atmosphere and reach orbital or escape velocity.

There are not many airless worlds that would have gravity higher than 1G (most worlds that massive would have an atmosphere) so that would be encountered much more rarely, but it could be a problem there since I think the horizontal or vertical takeoff wouldn't be an option. I think.

The problem with Traveller ships being able to fly is directly related to their mass and the lifting effect of wings. Basically speaking they mass too much. Even the Space Shuttle, which weighs in empty at about 165,000 pounds is a flying brick - and it's wings don't provide a lot of lift. Traveller starships have to be pretty massive - their armor is crystal iron not lightweight aluminum and polymers. The Type-S is a lifting body style craft, but even that would be too heavy to generate much lift from it's shape. It would need actual wings, with a relatively generous wingspan. Granted, the M-drive would give it a pretty good thrust to weight ratio, but it just gets worse going up from there. Let look at a Subsidized liner. It has no lifting body design, and it's quite non aerodynamic. It also has no control surfaces. Yet it can land on the surface of a planet. So how would it get there?

For a civilization that has antigravity vehicles it makes no sense to not equip a starship with the same capabilities so that they, too, can easily maneuver in a gravity field. If we had antigravity today you can bet you would see airliners replaced with craft that can take off and land vertically. Cars would be replaced with grav vehicles as well. The only thing keeping wheeled vehicles around would be cost, and that you can do some things in a car on a surface that you can't with a grav vehicle in the air.

 

[fusor]

The problem with Traveller ships being able to fly is directly related to their mass and the lifting effect of wings. Basically speaking they mass too much. Even the Space Shuttle, which weighs in empty at about 165,000 pounds is a flying brick - and it's wings don't provide a lot of lift. Traveller starships have to be pretty massive - their armor is crystal iron not lightweight aluminum and polymers. The Type-S is a lifting body style craft, but even that would be too heavy to generate much lift from it's shape. It would need actual wings, with a relatively generous wingspan. Granted, the M-drive would give it a pretty good thrust to weight ratio, but it just gets worse going up from there. Let look at a Subsidized liner. It has no lifting body design, and it's quite non aerodynamic. It also has no control surfaces. Yet it can land on the surface of a planet. So how would it get there?

For a civilization that has antigravity vehicles it makes no sense to not equip a starship with the same capabilities so that they, too, can easily maneuver in a gravity field. If we had antigravity today you can bet you would see airliners replaced with craft that can take off and land vertically. Cars would be replaced with grav vehicles as well. The only thing keeping wheeled vehicles around would be cost, and that you can do some things in a car on a surface that you can't with a grav vehicle in the air.

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.

 

[Infojunky]

If that's the case then how does the classic Scout or Free Trader land? Traders and scouts are supposed to be land anywhere on planets to do their job. This goes against all the illustrations and concepts these ships stand for.

I have never assumed that they do NOT have contragravity capabilities. I will have to look at my GURPs books to see what they say.

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.

 

[AnotherDilbert]

The problem with Traveller ships being able to fly is directly related to their mass and the lifting effect of wings. Basically speaking they mass too much. Even the Space Shuttle, which weighs in empty at about 165,000 pounds is a flying brick - and it's wings don't provide a lot of lift. Traveller starships have to be pretty massive - their armor is crystal iron not lightweight aluminum and polymers. The Type-S is a lifting body style craft, but even that would be too heavy to generate much lift from it's shape. It would need actual wings, with a relatively generous wingspan. Granted, the M-drive would give it a pretty good thrust to weight ratio, but it just gets worse going up from there. Let look at a Subsidized liner. It has no lifting body design, and it's quite non aerodynamic. It also has no control surfaces. Yet it can land on the surface of a planet. So how would it get there?

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).

For a civilization that has antigravity vehicles it makes no sense to not equip a starship with the same capabilities so that they, too, can easily maneuver in a gravity field. If we had antigravity today you can bet you would see airliners replaced with craft that can take off and land vertically. Cars would be replaced with grav vehicles as well. The only thing keeping wheeled vehicles around would be cost, and that you can do some things in a car on a surface that you can't with a grav vehicle in the air.

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.

 

[AnotherDilbert]

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.

I have not considered this in detail, so I may be completely off.

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.

SDBs are supposed to be able to hide in the GG, so they might need anti-grav unless they can vector the M-drive.

 

[Sigtrygg]

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.

Where is it in 77 edition?