Anti Grav Dilemma

[Icosahedron]

How does anti-G work?

This is a distillation of various threads (thanks to all who contributed previously) outlining the dilemma as I see it.
Note that this is not just a Traveller problem, but affects many sci-fi scenarios using Grav tech.

Unless you can figure it better than me, there must be at least four different types of anti-G, because the requirements differ dramatically according to context and range. I've tried my best to glue some logical mechanisms to them but, as you can see, I'm struggling. Any comments? Suggestions?


Firstly, deck plates and ground skimmers must have a localised surface effect that drops away rapidly with distance, otherwise cumulative gravity effects would influence things several decks away, and ground skimmers would be able to fly high.
If the formula is the standard inverse-square law, Skimmers would be limited to a few metres from min to max ride height (which is fine) but a consequence of this is that there would be severe tidal effects over a 3m deck height. This could be reconciled by having bipolar (back to back) deck plates that pull from below and push from the deck above, thereby minimising the tidal effect.

My mechanism:
This is Surface Effect Grav Resist SEGR. Ride height is nominally 0.5m, but the drive is designed to cope with ride heights of up to 4m (NOE convenient handwave). Each doubling of the ride height will increase fuel consumption by 4 times (Inverse-square Law). Travelling at 4m will therefore reduce range by 64 times! Grav belts are generally used at between 1m and 2m ride heights to keep legs off the ground, and are consequently comparatively thirsty.
Deck plates are 0.5m under the deck, providing a force of 1G at deck level, 0.25G at stomach level and 0.0625G at ceiling level. The overhead plates add 1G at ceiling level, 0.25G at stomach level and 0.0625G at floor level. Tummy float, but otherwise stable. Carry a little paper bag!


Another application is the Tractor/Repulsor beam, which projects a force of 10G+ over a distance of about 10^8 metres. Using the inverse square law again, this would require the force at the near end (projector orifice) to be 10^16 times larger than the force at the business end of the beam. Surely that would have an unattainable power demand? And I wouldn't want a field of over 10^17G aboard my ship anyway! Again, this is a force between two small masses. (and yes, I know I'm using the term 'force' sloppily.)
What happens if a repulsor is aimed at a missile fired from a planet? 10G force is projected between ship and missile AND between ship and planet! That's gonna wreak havok with the inertia compensation!

My mechanism:
Dunno what to do with this one yet! Can't even get started on it. It obviously works on a very different principle.
Could it affect Newton's 1st Law rather than his 3rd? Perhaps it projects a vortex in which objects at rest undergo a negative acceleration, objects at contant velocity come to rest, and objects under constant acceleration proceed at constant velocity? Just brainstorming aloud here. Need to figure a rate of change.


A third application is the Grav vehicle, which has a pretty uniform repulsive force throughout the thickness of the atmosphere and maybe some way into orbital space. If using inverse square, this can only work if it is calculated from the centre of the planet, like normal gravity - if it were calculated from the plate surface, then like the Tractor beam, distances would be far too great and the power demands far too high. This is clearly a force between a large body and a small one.

My mechanism:
This is Planetary Mass Grav Resist PMGR. There is no set ride height, but the amount of thrust generated is inversely proprtional to the local gravitational field. Grav vehicles cannot effectively function with a thrust below 0.1G (convenient stall-equivalent handwave) so for a drive rated at 1G on Earth, the inverse square law will give it a ceiling of about 3 planetary diameters, more than enough to reach low orbit and rendezvous with spacecraft. The most powerful G drives normally encountered, at about 10G will have a ceiling in the region of 10 planetary diameters. Obviously, this is still nowhere near stationary orbit, and spacecraft are therefore required in order to dock with Highports.


A fourth application is the 'reactionless' drive of deep space, presumably thrusting against microgravity. Again, this would suggest very long range forces at enormous power requirements. Even if it uses the same principle as the grav vehicle, pushing a small body from a large one, the power requirements must be many millions of times higher.

My mechanism:
Known as Stellar Mass Grav Resist SMGR, this is essentially the same as PMGR, but instead of being inversely proportional to the local gravity field, its thrust is - astronomical???
Again, dunno on this one because the G-field of our sun varies by a factor of a million or so from a close orbit to orbit 50. How do you get a constant thrust generated over this field strength range? Looks like mine will have to be torch ships, unless somebody can come up with a decent rationale. Maybe it works like the Repulsors?


Is it possible to figure out a single mechanism that will explain all four of these thrust types? If not, can you reduce the number of mechanisms below four? How can you get over some of the impossibilities of power and scale? How do you make it all logically self-consistent?

I'm fairly happy with mechanisms 1 and 3 now, but I haven't a clue about a mechanism to make tractor beams or 'reactionless' thrusters work.
All suggestions gratefully received.

 

[Renaissance Man]

Okay, for those who have an inkling of physics knowledge, please don't laugh

The difference between gravity technology, typified by the CG/M-drive divide, for me was about the presence of a native gravity field.

In CG, the technology manipulates existing graviton fields, shunting heavy graviton streams around the craft (or anti-grav harness), with appropriate "pinches" to generate thrust.

As the native supply of gravitons thins out, there is less and less to manipulate, attenuating the effectiveness of CG. Inertial dampeners also work on the principle of shaping and pushing away the gravitational effects of velocitized mass.

Thruster plates, and other applications of gravity tech like repulsors/tractors are an improvement on CG in that they actually generate a gravity field where none would otherwise be available. Gravity projectors can create a gravity well directly outside the ship that pulls the ship toward it, like holding a carrot in front of a donkey, so to speak. Articulating the gravity projector array in various directions allows thrusters to pull the ship in any direction, and in general create a gravity field in any shape as needed. With specialized gravity projectors with a greater range than thruster plates (while using your thrusters to create a counteracting pull) and you have a tractor beam. Reverse the "polarity" (anti-gravitons? gravitons with a different "spin"?) and you have a repulsor.

Deck plates are in some way between these two techs, relying on a graviton "anode" and "cathode" above and below the deck and generate an even field that simulates a steady 1G. Err... or something like that.

...

Okay I admit it, I have no clue what I'm talking about. :rofl:

 

[Major B]

Icosahedron,

I'd love to add to the conversation, but I majored in History for a reason.

I can point you toward some similar information I found - I've been looking at in preparation for doing some MT ship designs. It is a breakdown of several alternate types of drives on Scott Martin's website (click on the 'alternate drives' link).

Hope that helps if you haven't already seen it. Without the ability to 'borrow' the ideas of smart people like you and Scott, I'm reduced to relying on deliberate handwaving.

 

[Icosahedron]

Thanks for the link, Major, I hadn't seen that site before. I'll have to dig out and blow the dust off my TNE book and check out HEPLAR.

Thanks for the compliment too, but as I intimated in my first line, the above ideas were based on contributions from a number of people.

RM, my designs may or may not work on some form of graviton manipulation. I don't want to open the can of worms inside the Black Box - none of us knows what we're talking about there, I just want to ensure that the way the Black Box claims to affect objects is logically consistent.

The Thruster plates from the link, for example, claim to require a local gravity field, but there is no rationale to explain why the plates generate the same thrust while the local gravity field varies by a factor of a billion between Stellar close orbit and the interstellar void.
Maybe they don't use the local field after all?

I think I need to check out WHY Newton's first Law holds true. Can anyone provide a shortcut on that?

 

[Uncle Bob]

OK, mass has two effects, gravity and inertia. For gravitics to work these have to be different, and there is someway of manipulating them seperately.

IMTU the maneuver drive works by Mach's Principle (Real Science, though an unproven theoy), that is inertia relates mass to the background mass of the Universe. By "pushing" against this background mass you get an acceleration that has the same Energy cost, no matter what distance from a particular object. REAL SCIENCE: Woodward had a contract to study this for NASA's Breakthrough Physics program. NASA's program was canceled in the 1990s, but he got some intriguing results.

For antigravity I don't like thinking about gravitons. They are only theoretical, squirrelly and counter-intuitive, and since I got a C in Quantum Mechanics and a B+ in Field Theory I will stay with fields, thank you very much. Assuming, somehow, you can create a gravity field independent of mass, I will blithely assume you can create a negative field. If the positive field of your four ton airraft interacts with the positive field of the earth to produce an attractive force of 40 kilonewtons, I can create a "negative" field that will repel at 40 KN (the Earth's gravity sees an illusion of a -4 ton mass and repels it) so the airraft floats. Manipulating the negative gravity field lets me maneuver, climb or descend, but it costs me energy. But it only works well near a planet, and it is kindly slow on a small planet or moon.

Note that this doesn't do skimmers or tractor beams. Fortunately, neither are canon and I don't use them.

Deck gravity is more problematic, requiring a lot of hand waving. Perhaps some kind of a "capacitor" effect between deck and overhead plates?

 

[Plankowner]

Maybe the problem is the idea of deck plate gravity.

Maybe instead of each individual deck having a gravity plate, there is a gravity plate at the "bottom" of the ship that creates a gravitic field above it. The hull of the ship has contra-gravity built in to negate the effects of inside (and outside) gravity, which is called Inertial Compensation.

If you lost the hull CG, then the internal gravity field would be affected by outside gravity and would vary. It would also be detectable like any other gravity field.

Perhaps at lower TLs, these gravity generators can only produce gravity like a point source (mass), at higher TLs, the gravitic attraction can be spread out (in a limited way) in 2D, creating LINES of gravity. These lines can be "woven" into a mesh which simulates a plane, creating "gravity plates".

Only the point mass uses the Inverse Square Law, the line or plate follows some different rules until you are far enough away from the plane to treat it as a point mass. Thus the gravity between one deck and another is not as bad as the Inverse Square Law would lead you to think. I don't remember the exact numbers for lines and planes, but I am sure someone can provide that data.

Some interesting effects from this idea...

Destroy the hull and the "Gravity" of the ship increases, possibly creating hazards to nearby shipping; depending on how your artificial gravity field is generated (negative matter or through some energy application?)

Regarding "Speeders" and Air Rafts...
They use the same technology which is to create a negative gravity field. It is all about compensation. Speeders cannot adjust their CG compensation quickly, so they tend to stay at relatively the same "height" as the Center of Gravity (middle of the planet). They can slowly compensate which allows them to follow terrain. Air Rafts can change the CG compensation in seconds, or less, allowing them to control the altitude of a vehicle efficiently.

 

[Foxroe]

I think that if we knew how to properly implement manipulation of gravity in the Traveller universe, then we would be one step away from it in reality. We would be spending our time chasing Nobel prizes and government grants, and not playing Traveller.

One thing that always bugged me about theorizing about how this stuff works, is that even when you hand-wave and say “this device creates 1G inside my starship”, what happens when it loses power (i.e. the PP is destroyed)? What happens with a hull hit; does it disrupt the ability to artificially generate gravity in the vicinity of the damage? Will the crew be reduced to hamburger as a result?

IMHO, it’s probably best to just Google the internet and pick and choose which theory you like best, and stick with it for your TU. Regardless of what you pick, it’ll be one huge hand-wave.

Of course, an alternative is to start your TU from scratch, and assume that it was never possible to harness gravity in the first place. So only small airframe-type ships could enter a world’s atmosphere, maneuver drives are not reactionless, all your starship decks would need to be oriented perpendicular to the axis of movement (or be equipped with spinning habitats), air/rafts are actually VTOL vehicles, etc., etc. … but then you would just be playing 2320AD at that point.

-Fox

 

[Ishmael]

Of course, an alternative is to start your TU from scratch, and assume that it was never possible to harness gravity in the first place. So only small airframe-type ships could enter a world’s atmosphere, maneuver drives are not reactionless, all your starship decks would need to be oriented perpendicular to the axis of movement (or be equipped with spinning habitats), air/rafts are actually VTOL vehicles, etc., etc. … but then you would just be playing 2320AD at that point.
-Fox

yes!!!! That's the ticket!
The way canon ought to be!.....
<-- blatant heretic

( okay..a very minor nod to cg tech..."potential field generators" to give air rafts but otherwise too power hungry to be rampant as cg in the OTU..... I love trains and ships and zeppelins and hovercrafts and WIGS..and...and ....)

 

[fredofmars]

<snip>Deck gravity is more problematic, requiring a lot of hand waving. Perhaps some kind of a "capacitor" effect between deck and overhead plates?

Perhaps it's more like the electron space charge between the anode and plate in a vacuum tube. There would be a difference in gravitational "potential" between the floor and ceiling grav plates, and the graviton particles would tend to pool toward the floor plate.

Fascinating things, vacuum tubes. I'm in the middle of a book on them.

 

[Uncle Bob]

You have to be careful, though. Gravitons are not electrons, they are analogus to photons in quantum EM theory. That's why I stick to field theory.

 

[fredofmars]

You have to be careful, though. Gravitons are not electrons, they are analogus to photons in quantum EM theory. That's why I stick to field theory.

I'm not a quantum physicist, so I'm not going to argue that point.

I'm saying there might be an effect between floor and ceiling grav plates that could be sufficiently similiar to the electron space-charge that such a comparison might be useful to those who are familiar with a tube type of setup.

 

[Icosahedron]

This is the very reason that I chose not to open the can of worms concerning 'how they work', and concentrated instead on 'what they do'.

It doesn't matter to me what process creates the attraction or repulsion; there is nothing but handwave in that direction. What I'm interested in is how objects within the field (/stream/array/whatever) behave and ensuring that such behaviour is both logical and consistent whenever and wherever the same technology is used.

This is what led me to the conclusion that there must be several different types of gravity manipulation, since the effects of Anti-G were incompatible between the areas I outlined in the first post.

What concerns me now is getting compatibility within each area eg:

If repulsors can move up to a metric ton of missile at a range of 50,000 miles, why don't they rip their own bay apart with a nearby force of around 10^17g? Why can they not blow a hole through the side of a nearby starship with irresistable force? Why can they not prevent a starship from closing to board?

If a 'reactionless' drive pushes against the local G-field, why does it have the same amount of push in orbit as it does in deep space, where the local field is many orders of magnitude smaller?

These are not questions about technological cause, but about logical effect - game-relevant effects, and these are the type of discrepancies I was hoping to iron out here.

 

[aramis]

The solution to the force issues for the bay is that the gravitics prject a distortion of local gravity, rather than a "bar of force" connecting the two bodies.

So the bay is projecting two/three/more interacting beams that result in changing the "gravitic altitude" of the spot they intersect in.

 

[Uncle Bob]

This is the very reason that I chose not to open the can of worms concerning 'how they work', and concentrated instead on 'what they do'.

It doesn't matter to me what process creates the attraction or repulsion; there is nothing but handwave in that direction. What I'm interested in is how objects within the field (/stream/array/whatever) behave and ensuring that such behaviour is both logical and consistent whenever and wherever the same technology is used.

This is what led me to the conclusion that there must be several different types of gravity manipulation, since the effects of Anti-G were incompatible between the areas I outlined in the first post.

What concerns me now is getting compatibility within each area eg:

If repulsors can move up to a metric ton of missile at a range of 50,000 miles, why don't they rip their own bay apart with a nearby force of around 10^17g? Why can they not blow a hole through the side of a nearby starship with irresistable force? Why can they not prevent a starship from closing to board?

If a 'reactionless' drive pushes against the local G-field, why does it have the same amount of push in orbit as it does in deep space, where the local field is many orders of magnitude smaller?

These are not questions about technological cause, but about logical effect - game-relevant effects, and these are the type of discrepancies I was hoping to iron out here.

Repulsors/tractor beams are not CT, so I can ignore them.

Maneuver drive interacts with "the background mass of the Universe", as in Mach's Principle of inertia. It does not interact with local masses, so distance from a planet has no effect. Also, relative speed does not require greater energy to increase (i.e., .5* mv^2 doesn't come in because speed relative to the background mass is so high that changes on the order of km/sec are essentially linear. That also implies power several orders of magnitude larger than Traveller seems to allow, but CT is vague so I let it slide.)

Anti-grav vehicles do interact with local gravity, so they are sluggish in high orbit or on moons or dwarf planets. And completely useless in deep space. Also, energy porportional to v^2 relative to the planet is needed, so it takes a long while to accellerateto orbital velocity with a modest power plant.

Land skimmers are not CT cannon, so I ignore them.

Deck gravity, especially "inertial compensation" for high-G maneuvering I can't make work. I live with it until I write my own game with spin habs.

 

[Foxroe]

Repulsors are not CT, so I can ignore them.

They're in Book5 (HG2).

Unless you're defining CT as Books 1-3...

-Fox

 

[Icosahedron]

Twin beam, nuclear damper style Repulsors are a good option.
I consider CT to be everything on the CD, but that's just me.
Land skimmers may not overtly be CT canon, but descriptions of tanks, pictures, etc. of flat-bottomed vehicles (which would be a fatal Achilles heel if they routinely flew high) suggest that land skimmers play an integral tactical role. YMMV, of course, but I'm trying to cover all bases with this thread.
Inertial compensation slipped by me - thanks for that, the system I outlined doesn't cover it.
Hmm.

 

[Uncle Bob]

Twin beam, nuclear damper style Repulsors are a good option.
I consider CT to be everything on the CD, but that's just me.
Land skimmers may not overtly be CT canon, but descriptions of tanks, pictures, etc. of flat-bottomed vehicles (which would be a fatal Achilles heel if they routinely flew high) suggest that land skimmers play an integral tactical role. YMMV, of course, but I'm trying to cover all bases with this thread.
Inertial compensation slipped by me - thanks for that, the system I outlined doesn't cover it.
Hmm.

I figured they were flat bottomed because, tactically they hugged the terrain for cover. Moving at altitude they are more vulnerable, whatever their shape. Recent experience with IEDs suggest if I were designing them now I would give them V hulls and skids like a Huey.

 

[Icosahedron]

I know what an IUD is, but an IED? Is it similar?

Yeah, I figured on V bases for high flyers, too. Retractable skids, of course?

I need to swot up on the links between gravity and inertia. I'll get around to it.

 

[jec10]

I figured they were flat bottomed because, tactically they hugged the terrain for cover. Moving at altitude they are more vulnerable, whatever their shape. Recent experience with IEDs suggest if I were designing them now I would give them V hulls and skids like a Huey.

Yes, a classic blunder in CT/Striker and MT design sequences is you can only make belly and deck flat so it takes a tremendous amount of armour to protect those faces of your grav vehicle from weapons like proximity mines or remote-controlled mines (aka IEDs) which can attack grav vehicles over-flying them. Likewise for speeders at altitude that may be engaged from far below.

 

[atpollard]

Yeah, I figured on V bases for high flyers, too. Retractable skids, of course?

With the new (T5) fusion PP/MD able to run for a year on it's internal fuel supply, actually landing (and skids) becomes optional.