LBB2 M-Drives in LBB5: When does it help?

[Condottiere]

I suspect in Mongoose maximum altitude is twelve hundred fifty kilometres.

 

[Grav_Moped]

I suspect in Mongoose maximum altitude is twelve hundred fifty kilometres.

Probably so. But what I'm getting at is that maneuver drives (and advanced grav drives) are different than the antigravity used by a TL-8 Air/raft (at least in LBB3). It's the difference between the concept of a helicopter that doesn't need rotors, and one of a blimp that doesn't need a gas bag.

 

[AnotherDilbert]

The maneuver drive provides as a minimum, 1G in any direction (based on its rating).

Not according to MT SSOM, 100% thrust in one direction, down to 25% perpendicular, and 10% opposite direction.

SSOM, p2:

An Air/raft neutralizes its own weight and has 0.1G acceleration (regardless of local gravity*).

Not according the detailed system in CT Striker (where I guess you got the 0.1 G):

CT Striker B2, p18-19:
Rule 53: Planetary Environment
_ _ The basic Striker rules describe conditions on an Earth-like planet (in Traveller terms, size 8, with a standard atmosphere). Planets with different sizes, gravities, and atmospheres will have various effects, as explained below.
_ _ A. Planetary Size: The distance to the horizon is the upper limit...
_ _ B. Gravity: Gravity affects movement of all vehicles and personnel, ...
_ _ _ _ 1. Movement: For the movement of all ground vehicles, ... Grav vehicles require a more complicated determination of movement. The movement rate is determined as outlined in the vehicle design rules in Book 3, but instead of subtracting 1 from the G-rating of the vehicle's drives, the local gravity is subtracted instead.

Grav modules just provides fixed trust, regardless of local gravity. Lower gravity = lower weight means more excess thrust. In lower gravity a grav vehicle is faster, or can carry more payload.

LBB1-3 never discuss grav vehicle performance in different local gravities. You may try to draw conclusions from what they don't say, among many things they don't say, but "absence of evidence is not evidence of absence".

 

[infojunky]

LBB1-3 never discuss grav vehicle performance in different local gravities. You may try to draw conclusions from what they don't say, among many things they don't say, but "absence of evidence is not evidence of absence".

Specifically in Book3 refers to Null-Gravity, which can be read gravity doesn't effect said craft, instead of thrusting against.

 

[AnotherDilbert]

But what I'm getting at is that maneuver drives (and advanced grav drives) are different than the antigravity used by a TL-8 Air/raft (at least in LBB3). It's the difference between the concept of a helicopter that doesn't need rotors, and one of a blimp that doesn't need a gas bag.

CT & MT agrav is just thrust, like a helicopter.
TNE contragrav is weight counteraction, like a blimp.
T4 contragrav is somewhere in between.

CT Striker B3, p8:
_ _ K. Grav Generators: A grav vehicle requires grav generators installed in its chassis. Each .02 m³ of grav generators produces 1 ton of thrust and requires .1 megawatts of power from the power plant. They weigh 2 tons and cost Cr100,000 per m³.

"1 ton of thrust" ≈ 10 kN thrust.

TNE FF&S, p75:
Contra-Crav
_ Many spacecraft have contra-grav (CG) lifters as fuel-efficient means of landing and taking off from a planet surface, and CC lifters are also used on grav vehicles. CC lifters do not provide thrust and so cannot physically lift a craft or vehicle. Instead, they neutralize most of the gravitational attraction of a world (approximately 99% of gravitational force, beyond which power use becomes prohibitive). This, combined with atmospheric pressure, will provide buoyancy in very dense atmospheres and so allow the craft to float at low altitudes, but usually CC is used only as an adjunct to the ship's thrusters. By neutralizing most of a world's gravitational field, a ship with only 1G of thrust can still escape the world's gravity well.
Note that CG does not reduce the mass of the ship, and so a 1G thruster will still only produce 1G of acceleration; CG merely negates the gravitational vector of a world.

 

[AnotherDilbert]

Specifically in Book3 refers to Null-Gravity, which can be read gravity doesn't effect said craft, instead of thrusting against.

How do make something unaffected by geometry of curved space-time = gravity?

How do you keep grav vehicles not fly off into space as the planet accelerates away in its orbit around the star? Gravity is what drags it along with the planet.

LBB3'77, p17:
Air/Raft (8) CR 6,000,000. Also known as a flier, the air/raft relies on solid state null gravity modules for lift and propulsion.

Lift is a force (thrust) counteracting (not negating) gravity, as from wings. This quote says it is thrust.


A device that produces (magical) thrust is much less fantastic that a device that makes an object immune to reality...

 

[infojunky]

How do make something unaffected by geometry of curved space-time = gravity?

How do you keep grav vehicles not fly off into space as the planet accelerates away in its orbit around the star? Gravity is what drags it along with the planet.



Lift is a force (thrust) counteracting (not negating) gravity, as from wings. This quote says it is thrust.

All I stated was the text as written.

Some flavor of gravity manipulation is indicated, but until you get to Striker there is no clear mechanism stated. (Hint MT counts as Striker, also note that Frank was the primary writer of Striker, and his views about how things work differs from Marc's)

Please note Striker doesn't match the previous text written in earlier works. Both in power consumption and in operation.

Then add in that world Gravity doesn't effect the stated operational parameters of Air/rafts and the like.

One can make a case that more than thrust is in play.

As a side-note TNE/FS&S Contragravity isn't a complete screening of felt gravity, thus some Gravitational friction does occur.

Finally, consider the "time to orbit" for air/rafts, they don't climb nearly as fast as just the thrust would imply.

 

[Grav_Moped]

Not according to MT SSOM, 100% thrust in one direction, down to 25% perpendicular, and 10% opposite direction.

I'm assuming the ship is capable of yaw, pitch, and roll. That is, the magnitude of available thrust is entirely decoupled from the local gravitational field.

Not according the detailed system in CT Striker (where I guess you got the 0.1 G):

Grav modules just provides fixed trust, regardless of local gravity. Lower gravity = lower weight means more excess thrust. In lower gravity a grav vehicle is faster, or can carry more payload.

LBB1-3 never discuss grav vehicle performance in different local gravities. You may try to draw conclusions from what they don't say, among many things they don't say, but "absence of evidence is not evidence of absence".

I'm pulling only the minimum information from Striker necessary to understand the characteristics of a vehicle created under a different rule set. Striker's grav drives may well work differently from those in LBB3 as of TL 8.

Actually, they have to. Stated top speed corresponds to 1.1Gs (per Striker), but nothing in the text says they can't be used on a Size 10 world.

 

[Grav_Moped]

As a side-note TNE/FS&S Contragravity isn't a complete screening of felt gravity, thus some Gravitational friction does occur.

Which makes for an interesting question: If an air/raft flies by neutralizing gravity's effects on the vehicle, shouldn't the occupants be weightless?

 

[infojunky]

Which makes for an interesting question: If an air/raft flies by neutralizing gravity's effects on the vehicle, shouldn't the occupants be weightless?

I can't say I have never considered that.

 

[Spinward Flow]

Which makes for an interesting question: If an air/raft flies by neutralizing gravity's effects on the vehicle, shouldn't the occupants be weightless?

Wanna lose weight fast?

{cue Air/Raft commercial}

 

[Condottiere]

Air/raft neutralizes gravity underneath it.

An air/mattresses neutralizes gravity above it.

An air/bubble goes both ways.

 

[AnotherDilbert]

I'm assuming the ship is capable of yaw, pitch, and roll. That is, the magnitude of available thrust is entirely decoupled from the local gravitational field.

Agreed, it has nothing to do with the local grav field, and everything to do with how the "thruster plates" are mounted in the ship.

I'm pulling only the minimum information from Striker necessary to understand the characteristics of a vehicle created under a different rule set. Striker's grav drives may well work differently from those in LBB3 as of TL 8.

Yet you are using Striker, to say that Striker does not apply. I would disagree...

Actually, they have to. Stated top speed corresponds to 1.1Gs (per Striker), but nothing in the text says they can't be used on a Size 10 world.

I think you are reading too much into a very brief description.

LBB3'77, p16:
Ground Car (5) CR 40,000. This is an ordinary self-powered vehicle suitable for local use in civilized areas or on roads. It has a range of 1000 km before refueling and is capable of speeds up to 150 km per hour. Usually, this type of vehicle (a sedan) will hold six passengers. Note that other models (convertibles, sports mod- els, limousines, trucks, motorcycles, unicycles, vans, etc) may be available at va- rying prices. Ground cars are unpressurized, and average about 2 tons in weight. The ground car is a mass production item specifically manufactured for a specific world; it will tend to malfunction when transferred to a world not similar to its world of origin.

We all know how cars work, does this describe all the characteristics of a car? Where does it say that a car is slower up-hill than down-hill? Where does it say that cars lose power at altitude and lower air pressure?

LBB3'77, p16:
Helicopter (6) CR 1,000,000. Single engine rotary wing aircraft capable of vertical take-off and landing, as well as maneuverability in tight places. This craft weighs one ton with a capacity for one ton of cargo and passengers. Range: 600 km; maximum speed: 250 km per hour. A larger version would be a twin engine cargo helicopter costing CR 2,000,000; weighing ten tons, and capable of carrying ten tons.

Can a helicopter work in all gravities and all atmospheric pressures? No.
Does the brief description say that, in detail? No.

 

[AnotherDilbert]

Which makes for an interesting question: If an air/raft flies by neutralizing gravity's effects on the vehicle, shouldn't the occupants be weightless?

Are you weightless in a blimp? No.

Weightless = Free fall isn't the absence of gravity, it's the absence of a force stopping you from plummeting down.
https://en.wikipedia.org/wiki/Free_fall
https://en.wikipedia.org/wiki/Weightlessness

Is the floor if the air/raft stopping you from plummeting to the ground? Yes.
Would you perceive that as gravity? Yes.
If someone dropped you from space, would you experience "weightlessness" while hurtling down (until you smacked into the atmosphere or planet)? Yes.


If an air/raft was completely decoupled from gravity it wouldn't stay near the planet, the planet would speed away in its orbit around the star, leaving the air/raft behind. If it can fly or orbit it is affected by gravity.

In essence you are suggesting that the air/raft is experiencing the star's gravity, but not the world's gravity. As gravity is curved space-time, it experiences some curvature, but not some similar curvature. Basically you are trying to disbelieve General Relativity.

 

[Grav_Moped]

Yet you are using Striker, to say that Striker does not apply. I would disagree...

I'm using the rule there that relates discretionary thrust to top speed (presumably under standard conditions). Reaching further into that system to effectively re-design a vehicle created under a different rule system -- which system, I'll grant, probably consisted of "just making it up" -- is neither appropriate nor necessary.

I think you are reading too much into a very brief description.

I'm surprised you're arguing against a "the rules are the rules" interpretation.

We all know how cars work, does this describe all the characteristics of a car? Where does it say that a car is slower up-hill than down-hill? Where does it say that cars lose power at altitude and lower air pressure?

It may not need to adjust for density altitude, if the car in question is electric -- but that's a side issue.

One thing it explicitly does not include is the effect of the weight of cargo (up to 4000kg) and passengers (maybe up to 300kg -- since the driver is mandatory, it can't be 400kg). If the Air/raft's drive system is purely thrust-based, reducing the weight carried should allow more force to be applied in the direction of travel and thus increase its top speed.

Can a helicopter work in all gravities and all atmospheric pressures? No.
Does the brief description say that, in detail? No.

All? No. A wide variety, especially if designed to do so? Probably, though it might require alternate rotor blade sets, gearbox modifications, and forced induction (or a non-combustion-based power source) to do so. NASA got a rotary-wing drone to work on Mars, after all.

 

[Grav_Moped]

Are you weightless in a blimp? No.

Weightless = Free fall isn't the absence of gravity, it's the absence of a force stopping you from plummeting down.
https://en.wikipedia.org/wiki/Free_fall
https://en.wikipedia.org/wiki/Weightlessness

Is the floor if the air/raft stopping you from plummeting to the ground? Yes.
Would you perceive that as gravity? Yes.
If someone dropped you from space, would you experience "weightlessness" while hurtling down (until you smacked into the atmosphere or planet)? Yes.


If an air/raft was completely decoupled from gravity it wouldn't stay near the planet, the planet would speed away in its orbit around the star, leaving the air/raft behind. If it can fly or orbit it is affected by gravity.

In essence you are suggesting that the air/raft is experiencing the star's gravity, but not the world's gravity. As gravity is curved space-time, it experiences some curvature, but not some similar curvature. Basically you are trying to disbelieve General Relativity.

The idea here is that this is what might happen if antigravity simply created a gravity-stopping barrier between the vehicle and the planet it's flying over. Yeah, curved space-time and whatnot -- but this is all fiction anyhow. And it's amusing to consider.

There are other ways you could do it (fictionally) that wouldn't have that effect.

 

[Condottiere]

You can check out any time you like
But you can never leave

 

[AnotherDilbert]

I'm using the rule there that relates discretionary thrust to top speed (presumably under standard conditions). Reaching further into that system to effectively re-design a vehicle created under a different rule system -- which system, I'll grant, probably consisted of "just making it up" -- is neither appropriate nor necessary.

There is no redesign involved, you are taking one part of rating vehicle speed rule, but discarding another part.

I'm surprised you're arguing against a "the rules are the rules" interpretation.

I would say I'm arguing what the rules actually say, not what the rules don't even discuss.

It may not need to adjust for density altitude, if the car in question is electric -- but that's a side issue.

An electric 2 tonne car with a 1000 km range at TL-5? I don't think so, we can't even do that today.
If it were an electric vehicle, does the description discuss how the range varies with outside temperature, as we know is does IRL?

One thing it explicitly does not include is the effect of the weight of cargo (up to 4000kg) and passengers (maybe up to 300kg -- since the driver is mandatory, it can't be 400kg). If the Air/raft's drive system is purely thrust-based, reducing the weight carried should allow more force to be applied in the direction of travel and thus increase its top speed.

Agreed. Vehicles are rated for full load to get presumably minimum rated performance. Nothing stops you from calculating current mass to get a current performance rating. MT specifies calculating both loaded and unloaded mass (well they say weight, but they mean mass).

All? No. A wide variety, especially if designed to do so? Probably, though it might require alternate rotor blade sets, gearbox modifications, and forced induction (or a non-combustion-based power source) to do so. NASA got a rotary-wing drone to work on Mars, after all.

OK, does it work without an atmosphere?
Does the description specify that?

LBB3'77, p16:
Helicopter (6) CR 1,000,000. Single engine rotary wing aircraft capable of vertical take-off and landing, as well as maneuverability in tight places. This craft weighs one ton with a capacity for one ton of cargo and passengers. Range: 600 km; maximum speed: 250 km per hour. A larger version would be a twin engine cargo helicopter costing CR 2,000,000; weighing ten tons, and capable of carrying ten tons.

Is that description a complete specification of how a helicopter works?

 

[AnotherDilbert]

The idea here is that this is what might happen if antigravity simply created a gravity-stopping barrier between the vehicle and the planet it's flying over. Yeah, curved space-time and whatnot -- but this is all fiction anyhow. And it's amusing to consider.

It's supposed to be scifi, not fantasy. Anti-gravity is completely fictional, but there are ways it might work, or not work, without completely upending physics.

 

[kilemall]

It's supposed to be scifi, not fantasy. Anti-gravity is completely fictional, but there are ways it might work, or not work, without completely upending physics.

So the key is to figure out what game/story effect you want then work backwards to a theory of antigrav that is consistent enough to maintain suspension of disbelief for you and your players.