What up G? Handling gravity IYTU...

[BytePro]

Classic Traveller uses 10 m/s² for G when calculating travel times. Other gravity references I'm aware of all simply reference 'earth gravity' as a unit. Air rafts use 'null grav' modules for 'lift and propulsion'. Book 2 combat states that gravity 'can' and 'may' alter a ship's vector. Book 5 mentions grav plates built into decks to counter maneuver Gs, gravitics covering anti-gravity, and repulsors making use of anti-gravity.

IMTU, things have changes on occasions, but generally my take has been:

• Ships can nullify gravity to allow wilderness takeoffs on 1G+ worlds.
• Grav plates can nullify up to 6G, and provide upto 1G of artificial gravity.
• Standard Earth gravity of 1G is set at 10 m/s².

So how do things work IYTU?

 

[aramis]

I allow gravitic and AG drives limited overthrust similar to (and inspired by) the the rules in SSOM...

Such overthrust requires frequent rolls; further, it increases power requirements by double the overthrust. (Military rating is the optimum power efficiency.) Further, the time between failure rolls decreases as the overthrust increases. If you fail the roll, you reduce the allowed overthrust and increase the difficulty of further rolls; on a success, you can either increase difficulty or decrease overthrust.


Likewise, 10% thrust 180° off axis (IE, reverse thrust), 55% at 90°, and 100% on axis.
Coupling the two, this means a 1G ship can land tail-down, nose over, and still take off again in up to 1.1G's; it can tail-land in up to 2G's...

 

[Icosahedron]

Alas, after 30+ years of playing Traveller, I have yet to solve the problems of Traveller’s Antigrav.

I’m happy for the grav modules themselves to remain ‘black boxes’ - I have no desire to invent any BS about ‘graviton flux capacitors’ or whatever inside the modules, I don’t give a monkey’s how they actually create a field, but I am interested in how that field interacts logically with the universe - and there are serious problems here.

My analysis suggests that there are at least four different types of Antigrav in Traveller, which interact with the universe in different ways.

1. Surface Effect. This is the Antigrav that operates Skywalkeresque ground skimmers (and possibly also deck plates). Obviously, this does not ‘negate planetary gravity’ or even push against it. If it coupled with the planet’s gravitational field in any way, it would be able to hover at 1000ft just as easily as 1ft. Ergo, it must operate on some form of surface effect, which falls off rapidly with distance from the local surface. In a similar way, the field from Deck 1 of a ship does not apparently add to the field of Deck 20, so perhaps deck plates use the surface effect too. Lateral thrust is a bit more ‘iffy’ but I think I have it covered - ish. I just wish I knew what property of the surface the field interacted with - it can’t be a gravity field.
My interaction mechanic is inverse-square wrt the surface. Deck plates can supply positive or negative thrust up to their design limit.

2. Planetary Reaction. This is the Antigrav that operates Air Rafts and other ‘free flight’ grav vehicles. It seems to function effectively independently of height above the ground, yet doesn’t operate in deep space, so the logical conclusion is that it takes the form of some type of negation of, or reaction against, the field of a gravitating body (I haven’t satisfactorily figured what happens to a person caught underneath such a vehicle). Many of my grav vehicles incorporate aerodynamic lift, too.
My interaction mechanic is inverse square wrt the planetary centre of gravity, but calibrated for optimal efficiency at 1G. ie if the local field is 1/2G or 2G, the thrust is reduced to 1/4. This enables grav vehicles (eventually) to reach close orbit, but there’s no way they’ll reach geosynch or a moon - you need smallcraft for that.

3. Reactionless Thrust. This is the ‘Antigrav’ that enables spacecraft to move through space without ‘Fusion Torch’ rocketry. The figures don’t hold up for it to be any form of reaction against planetary or stellar bodies, the fields in space just aren’t strong enough and fall off at the wrong rates. It is most likely some form of ‘Inertial Drive’ using Mach’s Principle or some such to thrust against the universe at large. Bit more of a handwave than I like - I’d love to tie this down a little more. Again, I don’t need to know what’s in the Black Box, but it bothers me that I’m not even sure how this particular black box interacts with the universe.
My mechanic here is that ships follow vectors as per LBB2. However, a M-drive incorporates both an Inertial Thrust and a Planetary Reaction thrust, enabling a ‘1G’ ship to lift from (and maneouvre near) a planet with up to a 2G field. Once you leave close orbit, the Planetary Reaction thrust becomes ineffectual. Overthrust is always an emergency possibility.

4. Repulsor Technology. This form of Antigrav is pure handwave. I cannot conceive of any logical principle that would enable you to ‘project’ a force of several Gs at a target tens of thousands of km away, without creating a field of billions of Gs at the ‘muzzle’ of the device. I like the idea of repulsors and tractors, but I’m unhappy at having no idea how they could function.

IMTU, 10m/s^2 is the ‘standard’ 1G. Earth happens to have a surface gravity just short of 1G.

 

[BytePro]

I allow gravitic and AG drives limited overthrust similar to (and inspired by) the the rules in SSOM...

That was my original approach (though not directional and not based on SSOM), but given common Bk 2 1G ships with 1G launches, my preference changed... I considered starports having large repulsors for protection from ships which could also be utilized for assisted takeoffs, and used that for a while. Then I integrated the null-gravity with other aspects, which 'solved' the takeoff issues for me and allows ignoring the gravity of suns and other bodies for routine interplanetary traveling, while still giving the option to take advantage of them (especially for combat).

Alas, after 30+ years of playing Traveller, I have yet to solve the problems of Traveller’s Antigrav.

I actually do have an approach that has served me well for wrapping the various gravitic handwaves together IMTU - of course it still has to violate physics (and some degree of logic) as we know it. But it also leverages them and takes a stab at in-game 'rationalizing' of null-grav, anti-grav, gravitic acceleration, repulsors (which only act at closer ranges - not 10's of km - is that in the rules somewhere?), and ignorable M-Drive power requirements. It isn't designed to handle the 'surface effect' drives you describe - though I could see that as a tuning and governor aspect. I.e. a they could be limited in altitude artificially for safety, convenience or simply regulation - and that gives players something else they can hack...

Don't recall my limited CT collection having 'surface effect' gravitic vehicles, only ground effect - all gravitic vehicles and devices (like grav belts) shared the air/raft's properties. Were 'surface effect' gravitic vehicles part of published CT?

 

[Rigel Stardin]

This is my take:

Repulsers and Tractors Beams: Low tech: Look at Star Wars Illustrated guides, they refer to these devices as more or less atmosphere drives. Repulsers and Tractor Beams under James White's Sector General series are beam based much like a PAW or Laser cannon. Therefore they have a limited range and are directional.

Grav-plates: Used to create artifical gravity on ships to produce gravity onboard ships.

Grav Drives: High tech: allows vessels to travel in space and atmosphere, perform right angle turns and vertical take off and landing.

 

[Timmy]

Another Take

The other option is to consider that gravitic drives operate by interaction with spacial curvature. Where gravity is greater, is in the locality of larger masses, the curvature is greater and the drives operatr more efficiently. This also accounts for drop off of drive potential as ships move further oout in a gravity well. The result is that a ship with a drive rated at 1g can lift off from a world with a surface gravity of 1.5g because its drives can operate more efficiently in this gravity well.

 

[samuelvss]

Grav IMTU

A
2. Planetary Reaction. This is the Antigrav that operates Air Rafts and other ‘free flight’ grav vehicles. It seems to function effectively independently of height above the ground, yet doesn’t operate in deep space, so the logical conclusion is that it takes the form of some type of negation of, or reaction against, the field of a gravitating body (I haven’t satisfactorily figured what happens to a person caught underneath such a vehicle). Many of my grav vehicles incorporate aerodynamic lift, too....This enables grav vehicles (eventually) to reach close orbit, but there’s no way they’ll reach geosynch or a moon - you need smallcraft for that.

Per CT, this is what I do, but I have no great math for it; I use the World Number= Hours to [low] orbit. When a ship is streamlined, though, it basically has the ability to do a Grav VTOL, As Well As using aerodynamic lift, however crude to allow more of the grab to be vectored rearward; this is until the craft has enough altitude to use its Fusion Rocket-esque maneuver drives to supplement.

Note that actual aerodynamic ground effects Do effect grab vehicles. I have Luke Skywalker's speeder as a low tech grav raft that can fly Faster close to the ground, and with turbofan thrusters, than it could with just grav thrust.

4. Repulsor Technology. This form of Antigrav is pure hand wave...enable you to ‘project’ a force of several Gs at a target tens of thousands of km away, without creating a field of billions of Gs at the ‘muzzle’ of the device.

{Original mangled by quotation!! ; ) }
Part of the wandwavium tech of grab IMTU is that it is focused; the normal grav plates are, at TL 10-, are projected at a right angle to the plate. This makes grab vehicles at TL 10 and below have to tilt to turn, and to have bad cornering. This is a huge tactical disadvantage to grab armored vehicle; to turn away, you expose your belly! At TL 11-12, standard grab plates can be focussed laterally, giving lateral thrust without canting the hull, but the performance still suffers. At TL 13+, this lateral focus comes with no penalty to performance. That which is not at the focus of grav energy feels no effect, except to the extent it nears the focal point. This, without too much critical thought, justifies how repulsers work, though I do not normally use them in my campaigns: they exist, just as the USS Nimitz exists in the world of All in the Family, but they don't even get a cameo!

 

[Icosahedron]

only act at closer ranges - not 10's of km - is that in the rules somewhere?

Don't recall my limited CT collection having 'surface effect' gravitic vehicles, only ground effect - all gravitic vehicles and devices (like grav belts) shared the air/raft's properties. Were 'surface effect' gravitic vehicles part of published CT?

I don't think the range of repulsors was mentioned, since they arrived with LBB5 which dispensed with range determination, but according to LBB2, combat/detection range was usually within a few hundred thousand miles.
I figured, way back when, that all the weaponry, including repulsors, functioned at those ranges. Of course, it could be that repulsors only work when missiles get very close to a ship, in which case tractors would also be close range devices like a tow rope. This alleviates some of the 'focused grav' handwave, but doesn't eliminate it entirely.

Surface effect vehicles may also be my interpretation. I'd seen Star Wars, so the use of the word 'sled' in LBB4 p46-47, 'Overview of military vehicles', along with the assertion that by TL12, 'all vehicles have sufficient free-flight performance that ground vehicles effectively no longer exist, having merged with aircraft.' led me to the conclusion that prior to TL12 many vehicles did not have much 'free-flight performance' and were effectively grav-powered ground vehicles similar to ACVs.
By the time I got Striker, ground-skimming NOE-only vehicles were already part of MTU canon, powered by a short-range grav-plate style structure on their flat bellies.

The other option is to consider that gravitic drives operate by interaction with spacial curvature. Where gravity is greater, is in the locality of larger masses, the curvature is greater and the drives operatr more efficiently. This also accounts for drop off of drive potential as ships move further oout in a gravity well. The result is that a ship with a drive rated at 1g can lift off from a world with a surface gravity of 1.5g because its drives can operate more efficiently in this gravity well.

Interesting take. 20 years ago I'd have jumped at the chance to figure out the repercussions of that idea. Now, I'm not sure I can be bothered to look up the formulae that used to be in my head.

Note that actual aerodynamic ground effects Do effect grab vehicles. I have Luke Skywalker's speeder as a low tech grav raft that can fly Faster close to the ground, and with turbofan thrusters, than it could with just grav thrust.

{Original mangled by quotation!! ; ) }
Part of the wandwavium tech of grab IMTU is that it is focused;

Yes, ground-effect vehicles are an alternative to surface effect grav.

So like a laser, with a uniform G-field all along the beam? Maybe, but the black box is getting a little heavy for its suspenders for my liking...

I just have to face it, I'm never going to be 100% happy with somebody else's invention. I'm sooo glad I made my own TU before I had to start rationalising the OTU. The hardware is bad enough, without the social and military anomalies.

 

[BytePro]

Of course, it could be that repulsors only work when missiles get very close to a ship, in which case tractors would also be close range devices like a tow rope. This alleviates some of the 'focused grav' handwave, but doesn't eliminate it entirely.

It never occurred to me they might work at farther ranges - probably the influence of some Sci-Fi book, or maybe I just wanted them to be limited (or its my limited mindset).

My formative CT year coincided with studying 'microelectronics' (as it was called) and I already had a good grasp on basic electronics and elementary physics and some smattering of the higher level stuffs - so I had the notion of a gravitational field and the graviton... plus the Higgs boson & field. Some nice RW science theories on which to hang my sci-fi hat.

I'd seen Star Wars, so the use of the word 'sled' in LBB4 p46-47, 'Overview of military vehicles', along with the assertion that by TL12, 'all vehicles have sufficient free-flight performance that ground vehicles effectively no longer exist, having merged with aircraft.' led me to the conclusion that prior to TL12 many vehicles did not have much 'free-flight performance' and were effectively grav-powered ground vehicles similar to ACVs.

Didn't have LBB4 for 4-5 years, and never really used it - but I can see how that quote would have affected things. (Glad I never bothered with it! )

I had seen Star Wars on the big screen twice before playing Traveller. The first time I was very young and thought the speeder was a ground effect vehicle - having 'ridden' above a huge air table at JSC around the time. So when I saw it again that notion must have been fixed in my mind.

...
The other option is to consider that gravitic drives operate by interaction with spacial curvature. ...

That option occurred to me as well and had a definite appeal - and it works well as an abstract handwave. Attaching numbers and game mechanics - not so much that I could determine (at least within my requirements).

Unfortunately, it complicates things as gravity is everywhere, falling away at the inverse square - and gravity and the space time curvature are tied in this fashion. Making up something else that doesn't work this same way (which is a fundamental geometric property) adds another handwave and I never came up with something uniform from spaceships to grav belts that was elegant and simple, in a larger framework, using this approach.

Further, I typically have adventures with worlds having 2 and 3, or more, standard gravities and like a framework that lets me play with a 'rationalization' of why I can ignore the messy stuffs while still retaining the goodness and reasonable limits.

If you've got some mechanics that work with this - love to hear them!

 

[Timmy]

Further to another take

I perhaps should have said that the drives act on the curvature of space-time, as this is what gravity is according to general relitivity. Where there is greater curvature, it is easier to get traction. Action on spacial curvature was the explanation given in MT for the ability of thrust plates to function at greater distances from planetary masses than standard grav drives.

 

[Icosahedron]

I perhaps should have said that the drives act on the curvature of space-time, as this is what gravity is according to general relitivity. Where there is greater curvature, it is easier to get traction. Action on spacial curvature was the explanation given in MT for the ability of thrust plates to function at greater distances from planetary masses than standard grav drives.

Sounds like a dose of BS from MT. There's no such thing as space curvature, as opposed to space-time curvature, and if they meant space-time curvature, then this is exactly the same as gravity so would have the same performance as standard grav drives.

Unfortunately, as I stated above, the field-strength and drop-off rates in deep space make it effectively impossible for M-drives to work via gravity/STC.

Hence, IMO, reactionless drives must be inertial, and when we eventually figure out how inertia works, maybe that will provide us with a M-drive.

I am interested in your idea for making grav drives stronger, rather than weaker, in high grav fields, though. As you say, it would mean that grav vehicles would be able to function in any gravity well that a human could survive, and the higher the gravity of the planet, the further out into orbit a grav vehicle could reach before it ran out of thrust. I really don't want to figure out the ranges for different planetary examples, though.

 

[BytePro]

Yeah, using 'anti-gravity' - i.e. reversing the gravitational attraction into repulsion has limiting range vs power issues. I considered this early on as it would allow 1G ships to land and take off from 2G worlds and fits the term 'anti-gravity'. To work as an M-Drive between planets would also require another form of gravity based acceleration. Which is not too bad either. I got the impression this was MT's 'BS' approach.

I choose a different 'solution' because these two alone make CT travel equations invalid and 'messy'. My aim was for a meta-game and in-game equivalent solution consistent and as simple as the rules already are. (My admittedly limited cloud level view of MT: aside from one really nice task mechanic aspect, it had no problem with adding complexity - well, other than errata, internal consistency issues, rationality, and post elementary physics )

Making gravitic tech 'work' using inertia manipulating tech provides a ready solution. Unfortunately, inertialess drive tech opens a whole can of logical worms. Decoupling inertia as a property of matter can let one have their cake and eat it too. Classically, inertia is treated as an intrinsic property of matter - but one could also, theoretically, treat it as an extrinsic property.

(Its not an unusual approach - I ran across theories and experiments related to doing just that (by real scientists as opposed to the con artists claiming inertialess and perpetual motion 'research') and they are still actively being pursued. LHC results might even provide some stimulus in this area in the coming years.)

 

[Ishmael]

Trav's grav tech just seemed too easy for my tastes. It made trains, plane, ships, etc. superfluous (not necessary or relevant; uncalled-for).

To tone it down a bit, I say that the energy input must be equal to the change in potential energy from ascending, and if the unit is shut off, the grav-thingy just falls (potential changes to kinetic).
This makes grav tech much more power-hungry than the standard rules which makes room for other forms of transportation to compete.

 

[aramis]

Trav's grav tech just seemed too easy for my tastes. It made trains, plane, ships, etc. superfluous (not necessary or relevant; uncalled-for).

To tone it down a bit, I say that the energy input must be equal to the change in potential energy from ascending, and if the unit is shut off, the grav-thingy just falls (potential changes to kinetic).
This makes grav tech much more power-hungry than the standard rules which makes room for other forms of transportation to compete.

Expense alone (using Striker or MT) puts gravitics off the plate, too.
Electric or ICE trains are fast, safe, and inexpensive. So are busses.

Fusion trains and busses can go WAY further per fueling than ICE, and are less infrastructure reliant, and fusion busses, even with the gross inefficiencies of small plants, provide safe, reliable and not terribly expensive ground vehicles with massive flexibility; grav vehicles are as much as triple the costs...

 

[Icosahedron]

I played with costs, too. It was easier than trying to figure some technical guff to explain ground vehicles.
I made it a requirement for grav vehicles to include the 'controls' from Striker's aircraft design sequence.
Likewise, I made 'skimmers' cheaper than 'free-flight' grav vehicles.

 

[BytePro]

Hah - explain petro fueled cars and energy generation - when the tech that didn't require such pre-dated them and is far and away superior in the economics of reality (vs. insane human socio-politio-economics) .

In the U.S., at least, most of the population would state that cars are the primary form of transportation.

The world has had vehicle tech for over a century - but well in excess of half the world's population gets by with bicycles or their own two feet. These places have access to the tech (even production), but history and human economics (as well as rational thinking in some small cases) result in it not being used.

By definition, the higher TLs provide for fusion power and gravitics - which frees a society from the massive infrastructure requirements of roads, power distribution, and consumable resource harvesting and their massive environmental impact (esp. considering multi - millennium societies).

Implied in the rules are that grav tech requires large power usage (fusion, and storage density in the case of smaller devices) and failure of gravitics means 'drop from the sky' - though failsafes and inherent design features may mitigate this (and are very likely). Sure, the TL and vehicles sections state that gravitics supplant other tech. But all the '70s crap tech and lower (much more so than the higher TL stuff) are there to use as you desire, regardless of what one or two lines state.

For my part - I consider that stuff the exception. My definition of 'Science Fiction in the Far Future' certainly doesn't include permissive inane primitive tech like internal combustion wheeled vehicles and other such absurdities - get real!

 

[aramis]

ICE does NOT equate to petrochem. Hydrogen turbine engines are also ICE. As are alcohol fueled engines.

burnable hydrogen is the cheapest way to store solar power without damage to the environment. You use solar to split water, and burn the hydrogen and oxygen to generate power and water for the vehicle.

 

[BytePro]

Nah - especially in the far future - direct storage and release is the best way... no need to burn anything.

 

[aramis]

Nah - especially in the far future - direct storage and release is the best way... no need to burn anything.

I cannot agree, since even given the rather impressive direct storage methods, it's not energy dense enough for grav vehicles nor high speed rail.

And it's absolutely worthless for most gravitic craft.

Meanwhile, burning Hydrogen with atmospheric oxygen is MUCH lighter, and still more energy dense by about an order of magnitude.

 

[Ishmael]

Expense alone (using Striker or MT) puts gravitics off the plate, too.
Electric or ICE trains are fast, safe, and inexpensive. So are busses.

Only if the infrastructure of roads and railways are already in place. This includes such things as tunnels and bridges. Even then, taxes or someone must pay for upkeep of them.
Given that modern trackage ( plus signalling) can cost anywhere between 3 to 30 million dollars per mile for roadbed, track, and signalling and the maintenance costs associated with keeping them serviceable, noone is going to choose to use trains when grav-tech is available since it doesn't require all that stuff even if a grav train does cost 3 times as much as a diesel rail train.
The same would apply for ground vehicles of other sorts.
Hence, at tech 10, land and sea transport merge with grav transports.