Traveller with No/limited Gravitics?

[Meeko100]

This is a interesting idea I had been kicking around for a week, That how would the Tech change if Gravitics didn't exist, or if it was limited to working as artificial gravity (Diminishing returns making large systems to pull ships impractical, Only being able to pull {the tech only amplifies the force of gravity it is throwing around, can't reverse it})

Obviously Grav Vehicles and Grav Based M-Drives wouldn't Work. I figure that The Ships could be powered by Ion (or a subset of them, I personally have a preference for the VASIMR Style Engines for it) drives in space and have Reaction Drives for landing on planets. The Air/Raft could be replaced with a small shuttle. Maybe it could be a Hovercraft instead of using Gravity. Wouldn't be able to go into orbit though...

I figure Battle Dress Might have to changed a bit (Tank Level Protection becomes impractical at Tank Level Weight). Fusion Reactors may be bigger if Grav tech isn't there to make them teeny to fit on a Scout Ship. I'm not sure how bigger it might go though. 20%, 50%, 200%? Might be able to explain it as magnetic and superconductor tech got more research since it was needed more for the Power Systems.

So. What else might have to be changed for a Setting like that?

 

[aramis]

The first change is that ships no longer get to pull more than 3G's for even a full combat round. 6G drives are pretty much worthless.

The second change is that laser ranges drop. The OTU lasers are way too long for anything but gravitic focus. Which means you may want a shorter combat round.

The third major change is that trade drops by a couple orders of magnitude. This is in part due to the costs of orbit climbing due to the increased expenses and reduced payloads of shuttles. And also due to the longer times to jump points. Both of which must needs be amortized into the shipping costs.

4th, and most important, is that non-self-sustaining bases must have stronger rationales to exist. Since food costs going up for such bases makes them more expensive to operate, and this trickles to increase the basic costs of what they can provide, you're not going to see nearly as many space habs. The ones seen are more likely to be O'Neil cylinders and equivalent.

5th, trade bases will exist near the jump points of worlds orbiting major stars. Due to the longer trips in and out, low cost low thrust trade-boat trips to/from the trade base become the default, and ships don't trade at the world.

 

[TheDS]

I'm not so sure high-G maneuver drives will become useless. G-tanks provide a weightless environment, regardless of gravity. Battlestations might require you to get into a big bathtub. The human body is mostly fluid, and so should be able to sustain 6Gs without severe difficulty.

 

[GypsyComet]

Most editions assume that M-drives are gravitics of some sort, so you may also be transitioning to reaction drive. That changes the ship design balance completely.

 

[Meeko100]

Most editions assume that M-drives are gravitics of some sort, so you may also be transitioning to reaction drive. That changes the ship design balance completely.

Well, the reaction drives are there just for in atmo operations. Better to say jets, but not every world may be able to burn jet fuel. The space operations would be purely with the ion engines, with the reactions likely just being some maneuvering thrusters if they are fired at all. Mongoose HG also covers reaction drives, and I'm using those rules, so that's covered. The real trouble would be keeping track of the 3 fuel types (Hydrogen, Oxidizer, and the gas for the ion drive)

I didn't think about the changes to ground to orbit trade. But, I think it may not be to terrible. To my knowledge, pure hydrogen CAN be used for reaction drives, so the oxidizer would be the only addon to the load. The cost of getting to orbit would need to be determined using reaction drives. I'm sure it tacks on some amount of cost to shipping.

 

[Orr]

(Diminishing returns making large systems to pull ships impractical, Only being able to pull {the tech only amplifies the force of gravity it is throwing around, can't reverse it})

I don't quite understand what you mean by "pull" in those sentences.

I figure that The Ships could be powered by Ion...

With ion engines you won't be getting anything near the in-system performance of the OTU's maneuver drives. Among other things, it's going to take far longer to reach that planetary and/or stellar 100D jump limit.

So. What else might have to be changed for a Setting like that?

Lots of immediate effects and even more follow on effects. For example and as Aramis already explained, your cost-to-orbit will be closer to what we see now than what is assumed in the OTU. That's going to strangle trade.

 

[aramis]

I'm not so sure high-G maneuver drives will become useless. G-tanks provide a weightless environment, regardless of gravity. Battlestations might require you to get into a big bathtub. The human body is mostly fluid, and so should be able to sustain 6Gs without severe difficulty.

Except that NASA's own experiences with that show that it doesn't do much past about 5G - the heart still has to push blood uphill into the toes, nose, eyes... being immersed in fluid doesn't make that any the easier (in fact, mechanical pressure on the projecting surfaces and abdomen will make that even harder).

Being in flotation does NOT negate gravity nor acceleration forces, nor reduce the difficulties of moving fluids against gravity/acceleration. It DOES reduce physical stresses on bones and downside tissue (by not compressing it against padding), but blood flow isn't helped by that, and total immersion puts mechanical pressure on the topside that increases the effort needed for breathing and circulation.

 

[mike wightman]

I remember a quote from The Forever War:

"What happens when you drop a hammer in a submarine?"

Anyway, more on topic.

Remove the grav technology but keep cheap, efficient, small fusion power plants and your ships can generate the electricity they need for the ion/plasma engine. You can even use your fusion power plant to heat atmospheric gases in your hybrid jet/rocket interface drive.

If you keep the jump drive and its fuel requirements then you have a gas reserve for your plasma engine (low thrust but long endurance) and for your rocket (high thrust but lower endurance).

This pretty much re-invents HEPlaR from TNE, but with a dual mode operation.

 

[kilemall]

I have a completely different take on gravitics then most people. It's buried in my IMTU thread but I'll summarize.

Gravitics works, but it's purely repulsor tech- no grav decks 'pulling' and no tractor beams.

So the air/rafts on up are pushing against gravitic fields, and as they get away from stronger fields they lose 'push/lift'.

The HG repulsors are having to really work overtime to deflect missiles as they are such small objects, but flipside they are small objects and so more readily 'pushed' then say 'pushing away' a ship.

So to get ship gravitics you actually have a repulsor in the ceiling pushing down to get 'normal' 1G. It's not real gravity, but it is uniform acceleration against floor plates.

To deal with ship accel effects, the stronger repulsors are against the back wall/bulkheads of each compartment. They are pushing in sync with the maneuver drives to neutralize the effects.

However, these stronger repulsors have a technical limit, approximately 1G of effect at TL9, 2G at TL10, etc. You don't get evened out G effects until TL14. So people have limits to how much high end accel they can take- in the early going, Space Hurts.

Prior to gravitic tech of course you had higher G ratings possible, and so that part might be useful to your thought experiment.

The way it's handled IMTU is by designing the ships as horizontal building structures with the floors perpendicular to the line of thrust. So a constant 1-G accel effectively yields 'normal' G effects.

Flip the ship around at the halfway point for a minute or two of zero-G, then the decel phase still generates accel type G for our crew and passengers.

What you end up with is old school retro vertical atomic rockets.

 

[nobby-w]

This is a interesting idea I had been kicking around for a week, That how would the Tech change if Gravitics didn't exist, or if it was limited to working as artificial gravity (Diminishing returns making large systems to pull ships impractical, Only being able to pull {the tech only amplifies the force of gravity it is throwing around, can't reverse it})

...

So. What else might have to be changed for a Setting like that?

Many moons ago (1985 maybe), I did a campaign set in a TL 9/10 universe with no gravitics. It was originally inspired by Pournelle's CoDominium setting (Falkernberg's Legion etc.). This was before Aliens or 2300 came out, but the universe wound up being a bit more hard scifi-ish than the OTU, somewhat reminiscent of those settings.

• The setting was pretty much Earth plus a bunch of colony worlds. Some were more developed and some were very much colonies.
  
• Cheap starships run by a party weren't really a thing. Space travel was more expensive.
  
• Most starships were unstreamlined, with streamlined shuttles. I did VTOL craft with engines in articulated mounts that could point down to take off. Tail standing craft were used for specialist applications like heavy lift shuttles.
  
• Helicopters were very much a thing in those settings. Normally aircraft would have to get wings or rotor blades appropriate to the atmospheric density fitted. I also used the lighter-than-air transport from that setting, and mixed in prop-driven aircraft using piston engines that could be maintained locally.
  
• Off road trucks (something like a land rover) or larger ATVs were the typical mode of transport outside built up areas. If conditions were primitive enough then animal drawn transport was used. I didn't use miniphants (probably because I hadn't read that particular JTAS issue at the time) but I did have the notion of animals being shipped as embryos and raised by surrogate parents. My folks were growing an Angora Goat flock using super-ovulation and transplanting at the time.
  
• I did keep (relatively) portable fusion reactor tech. Larger ATVs or other vehicles could be fitted with a fusion power plant.
  
• Pretty much any space travel would be planetside - station - starship - station - planetside unless your party was the crew of a starship operating out in the cuds with no infrastructure.
  
• Most other tech was much the same as the OTU as of TL9-10.

 

[McPerth]

This is a interesting idea I had been kicking around for a week, That how would the Tech change if Gravitics didn't exist, or if it was limited to working as artificial gravity (Diminishing returns making large systems to pull ships impractical, Only being able to pull {the tech only amplifies the force of gravity it is throwing around, can't reverse it})

...

So. What else might have to be changed for a Setting like that?

My take is that, as in 2300AD (where gravitics don't exist), where it will be mostly felt would be in interface transport. Not being able to use gravitics to leave the worlds, reaction drives, catapults (to uplift), deadfall (to downlift) and (maybe) beanstalks would be the main ways for interface transport, while starships would be left in orbit to be serviced and loaded/unloaded.

Another important change would be about MD, that, expending reaction mass, would be more like TNE ships, with its endurance rated in G/hours, so maneuvering will be more difficult, and combat wil be quite more "static" (in the sense that less maneuver would be allowed).

 

[Orr]

Remove the grav technology but keep cheap, efficient, small fusion power plants and your ships can generate the electricity they need for the ion/plasma engine. You can even use your fusion power plant to heat atmospheric gases in your hybrid jet/rocket interface drive.

That's somewhat similar to David Drake's Lt. Leary/RCN series.

Fusion plants are "cheap/simple", meaning even barely literate people on backwater worlds can successfully operate and sort of maintain the plants which power their small, locally built "county craft". Fusion plants in turn power both plasma thrusters for atmospheric flight and antimatter thrusters for vacuum use.

The plasma thrusters use huge amount of water for reaction mass. So much so that topping off your tanks is your first priority after landing. Whenever possible, ships take off and land from protected pools, bays, oxbows, etc. The water helps mitigate the effects of the plasma thrusters and allows the ships to refuel by lowering a hose. Thanks to water landings and the peculiarities of the series' FTL system, ships are usually belly landing cylinders with retractable outriggers.

The antimatter system uses fusion power to first create antimatter and then mix it with normal matter in thrust cambers. This system can't be used in atmospheres because the conversion rate isn't 100%. Any "leftover" antimatter will combine with the atmosphere outside of the chambers to first damage those motors and eventually destroy the ship.

In space, ships barely thrust above 1 gee and many times use both their plasma and antimatter thrusters to do so. Ships in orbit routinely thrust in a 1 gee "powered" orbit for crew comfort/health but require constantly replenishment of reaction mass and/or large temporary dismountable tanks. Most ships, even warships, aren't designed to handle long periods of thrust above 1 gee and, like TNE's gee-hour restrictions, an eye must be kept on reaction mass levels. Fortunately, the series' FTL system doesn't have anything resembling 100D limits and in-system trips are routinely made by FTL.

If ships in Meeko's settings reach orbit with plasma thrusters, they're going to need to top off their tanks afterward. If they use plasma thrusters to clear the 100D jump limit, those trips will not be made under continuous thrust either.

 

[Meeko100]

What I was meaning when saying that what grav tech was there can only pull, is that it can only generate an attractive force. It caner repel objects. No repulsor tech.

I had another thought, on something to replace the gravitics in the MD. Found this interesting vid.

https://youtu.be/DP1q95f6TgA

To me, it seems to be that it is moving along the direction of current. I think I can use this idea, and size it up for use as a space engine. Using "Electrokinetic" sources of force to move the ship seems like it would work.

I still like the plasma engines in place of grav engines idea. I understand that Ion tech isn't as fast as rockets or grav, but I also figure that saying ion engines would apply to the category of plasma engines. None of them are as efficient as using gravity to do the work for you, but it would be almost comparable, bar the increase in general fuel use.

 

[WistfulD]

You have no idea how upset I was as a child to find out that the rocket ship slide we had in our local park was mass produced and thus not unique. :nonono:

 

[BillDowns]

If you are looking to replace Traveller's grav-based M-Drive, look into the EM Drive work by NASA. There have been several posts on the forum about it.

 

[whartung]

TNE was not "Grav free", but was certainly "less Grav", I think.

In TNE Gravity tech seemed to provide buoyancy, but not necessarily thrust.

 

[atpollard]

TNE was not "Grav free", but was certainly "less Grav", I think.

In TNE Gravity tech seemed to provide buoyancy, but not necessarily thrust.

... and focused lasers.

 

[aramis]

TNE was not "Grav free", but was certainly "less Grav", I think.

Not really - it was "no grav thrust, but LOADS more uses for AG/IC"...

In CT/MT, gravitics can produce external thrust.

In TNE, it apparently only works within a closed space - it can be used to accelerate things within other things, but cannot be used to move the gravitic unit itself. TNE also sets a cap - (TL)-8 G's, and allows doubling up for 50% more... but then has gravitic focusing on lasers (which needs 50G's+ to matter).

In TNE Gravity tech seemed to provide buoyancy, but not necessarily thrust.

Close, but not quite. The Contragravity lifters explicitly reduce the effect of gravity upon the shielded item by 99%. (BL Tech book 15; FF&S1 75). Almost all grav vehicles exceed 125kg/m3 (≅100x air density at STP), so they aren't floating, per se. They have to use thrust to remain airborne.