Traveller gravitic propulsion systems

[simonh]

This topic is split off from the "Gold pieces for credits" thread as we've strayed off into a detailed discussion of how Traveller gravitic drives might work.
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If you use an actual Grav drive (as MGT trav has it) then everything within the grav field (entire ship) gets moved at the same time. The artificial grav exists so that the people aren't in free fall the entire time. That would also explain why in Mgt, the fact that mass change in spacecraft does NOT affect performance. In FACT, that's the only logical conclusion given that fact.

In principle there are several ways a gravitic drive could work.

* It could create an artificial gravity field around an object, causing that object to 'fall' in the desired direction. In free space, occupants of a vehicle moving this way would experience freefall regardless of the acceleration of the vessel, if it didn't have some additional system to provide internal artificial gravity. I think this is what your talking about, but it's not in any way the only option.

1) It could act to attract itself, or repell itself relative to some external mass. This makes the most sense when the vehicle is near a planet, so e.g. the gravitic module could push against the planet's mass, accelerating it upwards away from the planet. Lateral motion could be generated by angling the drive to repel one side of the planet more than the other. The thrust generated this way would work more like a jet or rocket engine, but without any exhaust. Thrust would be transmitted mechanically from the drive, though it's mountings and into the structure of the vehicle. This would work best near a planet, but in principle you could point it at distant bodies. Mega Traveller assumed that gravitic vehicles worked this way.

2) It could be a graviton emitter. Again, this would work much like a rocket propulsion system, but the exhaust would be gravity waves. This is my favourite option.

3) Mega Traveller thrusters were not true gravitic drives, but were supposedly based on gravitic technology and worked by some kind of quantum interaction or other in the drive plates to generate magic thrust. Of the options above, I think this made them most similar to the graviton emitter. I'm listing them as an option as they have form in Traveller history, even though they're too vaguely defined to pin down exactly how they are supposed to work.

Edit - Finally you could have a drive capable of operating in more than one mode. So near a planet it operates in gravitic repulsor mode (2) for efficiency reasons, enabling it to counter the planet's gravity and still have it's normal rated thrust available for propulsion, and in deep space it becomes a graviton drive (3) at it's rated thrust. This might explain why ships with 1G rated drives are apparently capable of landing on and taking off from planets with 1G+ gravity fields, at least the obvious problems with this aren't discussed anywhere in the rules.

It's quite possible I may have missed something, but those are the options off the top of my head.

Simon Hibbs

 

[simonh]

Re-posting F33D's reply for context, I hope you don't mind. I've tried to fix up the quote bocks.
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1) It could act to attract itself, or repell itself relative to some external mass. This makes the most sense when the vehicle is near a planet, so e.g. the gravitic module could push against the planet's mass, a
2) It could be a graviton emitter. Again, this would work much like a rocket propulsion system, but the exhaust would be gravity waves. This is my favourite option.

Yes, but that would REQUIRE a drop off in efficiency. Which is not the case in Mgt. (I'm only referring to MGT rules. NOT other versions.)

3) Mega Traveller thrusters ...

Again this isn't MT and in MT MASS carried effected thrust. So, no.

In order to account for how the drive works in Monggose Trav it HAS to be something like I described.

 

[simonh]

I only included the MT stuff for completeness. I know MgT is not the same game, but since the MT drive says it is a development of gravitic technology it might be reasonably described as a gravitic drive. In which case, since MgT doesn't say what it means by gravitic drives, it's still potentially an option for referees out there that want to interpret things that way.

Anyway, more to the point, I don't see why a graviton emitter would drop off in efficiency far from a planet. It's conceptually just like a photonic rocket, but emitting gravitons instead of photons.

You may not have noticed this part of my post before replying, as I added it as an edit, bit it addresses your issue with efficiency further away from a planet or other gravity well:

Edit - Finally you could have a drive capable of operating in more than one mode. So near a planet it operates in gravitic repulsor mode (2) for efficiency reasons, enabling it to counter the planet's gravity and still have it's normal rated thrust available for propulsion, and in deep space it becomes a graviton drive (3) at it's rated thrust. This might explain why ships with 1G rated drives are apparently capable of landing on and taking off from planets with 1G+ gravity fields, at least the obvious problems with this aren't discussed anywhere in the rules.

So I'm basically just supposing that if graviton drives can have a secondary mode, to also work as gravitic repulsors near planets, that helps explain how the ship designs we see in Traveller art and deck plans can work.

Simon Hibbs

 

[Reynard]

They mention the maneuver drive is a gravitic drive in High Guard. I'm sure I'm missing the reference somewhere the large number of sourcebooks but is there an actual description of the Mongoose Traveller maneuver drive as only working in gravity wells or are we assuming from other editions? Looking at the Interplanetary Transit Time Table, flight beyond gravity sources is the rule.

 

[phavoc]

I've always assumed that the anti-gravity used when a ship is in a gravity well requires an opposing or greater set of gravity to work against. Thus antigravity vehicles like air/rafts are capable of reaching orbit but can't travel between planets.

The drive systems are bit more murkier, because they usually aren't specific or detailed enough to differentiate them. Some of the various rule sets (like MT) did try to go into more depth, however I think they also didn't stick to a single model and thus kind of mucked things up further.

 

[F33D]

I know MgT is not the same game, but since the MT drive says it is a development of gravitic technology it might be reasonably described as a gravitic drive.

No. In MT the description of how the M-drive actually works shows that it is NOT a Grav drive. The MT drive does not rely on gravity in any way.

 

[Condottiere]

It's abstractly vague enough to be the infinite improbability drive.

If it's directly derived from the gravitic technology that propels planetary grav vehicles, it would be a field effect.

 

[Reynard]

The description of the maneuver drive in MT states it is different yet similar to the grav drive, which also exists, and uses gravitic and nuclear damper technologies to react wit strong and weak nuclear forces for a reactionless drive not reliant on gravity wells. Mongoose keeps it simple and calls a maneuver drive gravitic.

I get the feeling gravitic drives and anti-grav tech use the creation of gravitons to give motion to a vehicle by negating a gravity source and thrusting a vehicle.

 

[F33D]

The description of the maneuver drive in MT states it is different yet similar to the grav drive,

No, it doesn't state that.

 

[Reynard]

"Thrusters are somewhat more advanced that gravitic drives but operate in a similar manner."
MegaTraveller Starship Operator's Manual page 2.

Had to recheck and slightly misread. You're right, I was remembering another reference that had gravitic drive and maneuver drive as two separate units, probably TNE or MM Traveler (or T20). So many references.

 

[dragoner]

IMTU, I break it up between Lifters, which is how an Air/Raft operates, and interacts with another gravity source, and Gravitics, which works by causing a curvature of space, and is the mechanism behind M-Drives, deck plates, and inertial compensators. Ships often have Lifters, and some small craft are entirely Lifter powered.

 

[Condottiere]

If you're willing to complicate the system, the field effect is less efficient than when it's directed in one direction, but the generators have to be built specifically for that mode.

The field effect needs to bite on some significant gravitational focus, and if I recall Tee Five correctly, there were three stages between one and a hundred planetary diameters.

The military may want speed that's more easily generated in a directed thruster, and could have lifters for cruising.

 

[simonh]

IMTU, I break it up between Lifters, which is how an Air/Raft operates, and interacts with another gravity source, and Gravitics, which works by causing a curvature of space, and is the mechanism behind M-Drives, deck plates, and inertial compensators. Ships often have Lifters, and some small craft are entirely Lifter powered.

I think it would make sense that gravitic propulsion that only works in a gravity field must be more efficient than deep space versions, because otherwise everyone would just use the deep space version as it's more generally useful.

Simon Hibbs

 

[Reynard]

Other editions of Traveller stated the gravitic technology is more limited and lower tech while thruster tech or maneuver drive tech, et al. is superior with the ability to travel beyond the limits of a grav well. Big difference is thruster/maneuver tech can't be miniaturized enough and gravitic tech is superior for non-starship/spaceship AG vehicles. Some references combine the techs to perform separate functions essentially making the starship also an AG vessel for efficiency which explains ships not needing to land on thier tails.

 

[dragoner]

IMTU, I break it up between Lifters, which is how an Air/Raft operates, and interacts with another gravity source, and Gravitics, which works by causing a curvature of space, and is the mechanism behind M-Drives, deck plates, and inertial compensators. Ships often have Lifters, and some small craft are entirely Lifter powered.

I think it would make sense that gravitic propulsion that only works in a gravity field must be more efficient than deep space versions, because otherwise everyone would just use the deep space version as it's more generally useful.

Simon Hibbs

Yes, lifters are able to be used in small applications, like Baron Harkonnen's suspensors, or other battery and fuel cell powered applications; the heavier gravitics take much more power, and usually are used with a fusion power plant.

 

[simonh]

Yes, lifters are able to be used in small applications, like Baron Harkonnen's suspensors, or other battery and fuel cell powered applications; the heavier gravitics take much more power, and usually are used with a fusion power plant.

That sounds right. For me the heavy duty verison would be a graviton thruster, with a secondary suspensor mode.

Simon Hibbs

 

[dragoner]

Yes, lifters are able to be used in small applications, like Baron Harkonnen's suspensors, or other battery and fuel cell powered applications; the heavier gravitics take much more power, and usually are used with a fusion power plant.

That sounds right. For me the heavy duty verison would be a graviton thruster, with a secondary suspensor mode.

Simon Hibbs

It helps reconcile the discrepancies between such applications as grav plates and air/rafts.

 

[Condottiere]

The field effect should be spherical, which would indicate that everything within in it, like a jump bubble, moves along with it.

Great for those missile pods.

 

[dragoner]

I'd make it directional, and the ship rides the effect like a surfer rides a wave, wave forms are common in nature.

 

[Condottiere]

If it's a field effect, you might want to centralize the drive, or distribute it around in sub-modules with overlapping mini-fields.