What if the tech levels came in at their originally stated decades?

[mike wightman]

I've always ruled it that the null grav modules of the air/raft requires a sizable mass to push against.
You could build a null grav drive spaceship for solar system exploration but it would be limited in that it could only apply its delta V while in proximity to a planet or moon, no course corrections without some other engine - ion or chemical rocket. Travel times are going to be much higher - weeks/months to get to Mars. The advantages are your payload is much larger and the spacecraft is much cheaper than the chemical/ion rockets it replaces (for the same payload).

The maneuver drive removes this limitation so that you can now constantly accelerate during your journey, so Traveller travel times can now be used.

 

[coliver988]

I've always ruled it that the null grav modules of the air/raft requires a sizable mass to push against.
You could build a null grav drive spaceship for solar system exploration but it would be limited in that it could only apply its delta V while in proximity to a planet or moon, no course corrections without some other engine - ion or chemical rocket. Travel times are going to be much higher - weeks/months to get to Mars. The advantages are your payload is much larger and the spacecraft is much cheaper than the chemical/ion rockets it replaces (for the same payload).

The maneuver drive removes this limitation so that you can now constantly accelerate during your journey, so Traveller travel times can now be used.

Those are my working assumptions as well: grav drives work against gravity aka mass. No mass around you, no thrust. Think gravity falls off with the inverse square of distance, but I just eyeballed as a remarkable coincidence with the 10 diameter distance to be at 1/10th portion of grav power, but 0 at 100 diameters. So while it can be used on a high orbit, you really want maneuver drives or something to make any significant delta V (outside of those slingshots!)

 

[mike wightman]

If the TL8 fusion reactor is small enough to go into a spacecraft then you have the option of a dual grav/plasma (or ion) drive.
The grav stage gets you into orbit and allows delta V to be spent while in orbital space, the fusion powered plasma rocket or ion engine can then be used while enroute.

You could also use 'drop tank' chemical rockets for high acceleration burns

If the fusion power plant of TL8 is too large to be put in a space craft there are other options - a solar cell power system, nuclear fission power system or an rtg to power the ion engine.

 

[Werner]

Who knows? Ask Marc. But air raft tech works on airless planets as it is a grav effect. Why would you think gases on a planet would be required for a gravity effect vehicle?

You use antigravity to repel the air molecules around the vehicle, since there are more air molecules below than above, this produces lift. Above the Moon, lower orbits are possible because there is no atmosphere. A gravity vehicle's main task above the Moon would be to achieve orbital velocity rather than altitude, it is repelling the Lunar surface. Gravity obeys the inverse square Law. Double the radius from Earth, you quarter the gravity. An Earth radius is 6400 km, an air/raft radius is about 10 meters, if you can focus antigravity downward, maybe you can have an effective radius of 1 km, so you have a tight beam of antigravity pushing downward at 1G, so at 1km under the air/raft the molecules weigh twice as much as they normally do, at 2 km, they weigh 1.25 times as much, this produces a downdraft, pushing mass downward pushes the air/raft upward according to newton's laws of motion.

 

[Proneutron]

You use antigravity to repel the air molecules around the vehicle, since there are more air molecules below than above, this produces lift.

No. Since in Trav they work on AIRLESS worlds this isn't how they'd work in Trav.

 

[Werner]

No. Since in Trav they work on AIRLESS worlds this isn't how they'd work in Trav.

I didn't say they didn't work, they just don't go as high, because they are only pushing on the Moon's surface, not its atmosphere.

 

[Proneutron]

I didn't say they didn't work,

No, you stated how they work (pushing around gases) that means they WOULDN'T work on airless worlds.

 

[boomslang]

No. Since in Trav they work on AIRLESS worlds this isn't how they'd work in Trav.

After literal decades of looking at it trying to make it make sense, I figure gravitics has two operational modes: antigrav and direct thrust.

Antigrav -- as used by ubiquitous "grav vehicles" -- works by reversing the gradient of the local gravity field, "nullifying" it and allowing the vehicle to hover, move laterally by tilting slightly, and slowly change altitude. This operational mode is very, very energy-efficient, which is why air/rafts (for example) can fly around for 10 weeks or so on a single charge-up or refueling. It does, however, require an external mass and associated gravity field to push against. Grav plates used in spacecraft decking work in a similar manner (from the mass of the vessel). The general operational limit for antigrav acceleration is 2Gs, as a result, in all applications.

Direct Thrust is a more complicated mode wherein the drive creates its own gravity regardless of local gravity fields (by pushing against the inertial frame of the entire universe instead). This is a much more energy-intensive process -- typically requiring a fusion reactor for power or else limiting flight time (in the case of, for example, a missile) to only a few hours if on batteries or fuel cells -- but it does top out at 6Gs, and is useable for interplanetary flight. Bearing in mind that the Solomani discovered Jump technology while mucking around with gravitics, if the vessel displaces 100dt or more, and has a computer to regulate the process, a gravitic drive, rather than simply pushing against its mountings, can form an inertialess field around the entire vessel, accelerating everything within at a uniform velocity, hence "acceleration compensation" and the radiation/micrometeoroid shielding mentioned in passing in Beltstrike.

Vehicles only have access to anitgrav mode; ships have access to both.

IMTU, as an interesting corollary, just as air/rafts can (slowly) reach orbit in antigrav mode, so can unstreamlined ships land and take off using it on worlds with Atmo-1+. Their operators just have to be patient and willing.

 

[Proneutron]

After literal decades of looking at it trying to make it make sense, I figure gravitics has two operational modes: antigrav and direct thrust.

Antigrav -- as used by ubiquitous "grav vehicles" -- works by reversing the gradient of the local gravity field, "nullifying" it and allowing the vehicle to hover, move laterally by tilting slightly, and slowly change altitude.

I simply have the drive create small gravity well(s) in the direction of desired movement. Above you makes you "fall up". Above and slightly ahead makes you go forward while maintaining altitude. No need for "negative" grav wells. We KNOW regular grav wells exist. Negative (hills) grav make not. But, whatever explains it so the players can work with it is good enough

 

[Werner]

No, you stated how they work (pushing around gases) that means they WOULDN'T work on airless worlds.

They push on mass within a certain distance, gas, liquid, solid, plasma it doesn't matter, but there has to be something to push on! In the case of planets with atmosphere, when the ground gets out of range it pushes on the surrounding atmosphere.

 

[Werner]

I simply have the drive create small gravity well(s) in the direction of desired movement. Above you makes you "fall up". Above and slightly ahead makes you go forward while maintaining altitude. No need for "negative" grav wells. We KNOW regular grav wells exist. Negative (hills) grav make not. But, whatever explains it so the players can work with it is good enough

That sounds like a Lorax drive. Do you know what a Lorax drive is? There was a book written by Doctor Seus called the Lorax, it was about environmental degradation, and in it was this creature called to Lorax, he was trying to convince the protagonist to stop destroying the environment for profit, well to make a long story short, in one scene the Lorax lifted himself up by the seat of his pants and pulled himself up through a hole in the clouds.

No matter how strong you are, you can't pick yourself up off the ground without pulling or pushing on something external to yourself, that is what I call the Lorax drive, because the Lorax just did something that was physically impossible, he violated one of Newton's three laws of motion, namely that every action has an equal and opposite reaction, which is why you can't lift yourself off the ground by your own seat of your pants, and why a gravity drive or any sort of drive must push or pull on something to achieve acceleration, and pushing and pulling on yourself will not work. On yourself the action and the reaction work on the same object, you, and unless you split yourself in half, you aren't going anywhere without pushing or pulling on something besides yourself.

 

[Proneutron]

No matter how strong you are, you can't pick yourself up off the ground without pulling or pushing on something external to yourself, that is what I call the Lorax drive, because the Lorax just did something that was physically impossible, he violated one of Newton's three laws of motion, namely that every action has an equal and opposite reaction,

That's isn't how gravity works. If you create a gravity well you WILL be drawn into it. You aren't picking yourself up. It isn't a tractor beam that you project and it curves around to grab yourself.

 

[Condottiere]

Tractor and repulsor beams would be negative and positive concentrations of gravitons.

 

[Proneutron]

Tractor and repulsor beams would be negative and positive concentrations of gravitons.

Not according to how they work on ST for instance. They work completely different than how a created gravity well works. They work like they are a physical "rope" or solid bar that extends away from the ship but is attached to the structure of the ship. Not a grav device at all.

 

[Werner]

That's isn't how gravity works. If you create a gravity well you WILL be drawn into it. You aren't picking yourself up. It isn't a tractor beam that you project and it curves around to grab yourself.

The source of the gravity is what pulls you, and whatever has greater mass will be less effected than the lesser mass object. If you put a 1g gravity field around a tennis ball, then on its surface will be 1g, if you go to twice its radius, it will be one 1/4 g and so on. So if you had a Starship and you threw a tennis ball with grav plating ahead of it, and then by remote control turned its gravity on, it will come flying back to the hull of the ship, bounce a few times and stick to the hull and the ship itself will barely move at all, because it has much greater mass. The same force is exerted on both the Starship and the tennis ball, because the ball has less mass, that force will move it more.

What you are describing seems similar to a warp drive, a typical warp drive as currently conceived consists of two rings, one at the front of the Starship and the other at the rear or bow and stern. These warp rings don't actually accelerate the ship, instead what the bow ring does is deflate space in front of the ship, while the stern ring expands space behind the ship, the velocity of such a Starship is not limited to the speed of light as that only applies to objects moving through space, not the contraction and expansion of space itself.

 

[Proneutron]

The source of the gravity is what pulls you,

The source of the gravity is the curved space. Mass emits gravitons which cause the space curvature. If by artificially creating "gravitons" at a point in space away from you it curves that space, you will fall towards it.

 

[Werner]

The source of the gravity is the curved space. Mass emits gravitons which cause the space curvature. If by artificially creating "gravitons" at a point in space away from you it curves that space, you will fall towards it.

A warp drive would do that be separating the virtual particle pairs in a vacuum, and then moving the positive particles to the forward warp ring and the negative particles into the rear warp ring. High densities need to be achieved in both rings to create the warp bubble. Velocity remains the same where ever the warship warps to, and upon collapse of the warp bubble the ship needs to match velocity with the destination (world/space station) in order to land/dock with it.

Suffice to say, this is not a standard Traveller campaign if a warp drive exists, not quite Star Trek either.

 

[Proneutron]

Suffice to say, this is not a standard Traveller campaign if a warp drive exists, not quite Star Trek either.

Yes, that's why I don't use warp drives.

 

[Werner]

Yes, that's why I don't use warp drives.

Not much different from hyperspace in Star Wars. Originally hyperspace was a shortcut through the 4th dimension, but it morphed into a kind of warp drive.