1g Ships and Size:7 worlds...

[Jame]

CT anti-gravity provides both lift and propulsion, it's just thrust (like a helicopter rotor). It has to be dimensioned for the amount of thrust it can provide, commonly measured in G of acceleration for the craft.
You are describing TNE contragrav, there is a difference.
There is no nullification, even in TNE, just counteracting, i.e. cancelling out with a counter-force.



That is TNE contragrav. Even T4 and T5 contragrav provides some slight propulsion. T4 contragrav provides a specified amount of lift, and has to be dimensioned for the gravity it's supposed to counteract.



CT does not have contragrav, but anti-grav. Anti-grav is just thrust, just like a M-drive.

And in sum, it still allows a 1-G thrust ship to land and take off from any world.

 

[AnotherDilbert]

And in sum, it still allows a 1-G thrust ship to land and take off from any world.

Yes, almost: It has limited thrust and can counteract a specified gravity, say 1 G, so no gas giant adventures are advisable.

And it has to be added to the ships at additional cost, tonnage, and power consumption.

 

[Jame]

Yes, almost: It has limited thrust and can counteract a specified gravity, say 1 G, so no gas giant adventures are advisable.

And it has to be added to the ships at additional cost, tonnage, and power consumption.

Good thing it's separate from the maneuver drive then, and is part of the ship's gravity system at no cost or extra power.

 

[AnotherDilbert]

..., and is part of the ship's gravity system at no cost or extra power.

Is it? Why?

 

[Jame]

Is it? Why?

Because in neither Bk2 or Bk 5 is it mentioned as a separate thing that needs to be added.

 

[AnotherDilbert]

Because in neither Bk2 or Bk 5 is it mentioned as a separate thing that needs to be added.

Agreed it is not specified as a separate system (it is in MT), but that does not necessarily mean it's standard:

LBB2'81, p28:
GRAVITY
_ _ The section on planetary templates later in this chapter covers the construction on specific world disks, complete with gravitation bands which can affect movement. When the vector of a ship passes through the gravity bands of a world, the gravity may alter that vector. During the movement phase, lay out the vector of the ship to determine where it will move. If the exact midpoint of the vector lies in a gravity band, a gravity vector will be added to the course vector to create a new vector.

Ships are affected by gravity, it's not optional.

Striker, B2, p41:
_ _ A. Movement: The movement rate of a spaceship is determined in the same way as that for a grav vehicle; the ship's maneuver drive rating is used as its G value. A ship with a G rating equal to or less than the planetary gravity may not take part in combat actions except from orbit.

Ships fly on their M-drive thrust, and local gravity is deducted from the M-drive. No free floating around...


If you want your ships to have anti-grav (or contragrav), they will of course have that in YTU, but by default they don't.

 

[Enoki]

The fun part is when you look at the Travellermap and the Vilani Main.

The thing that sticks out like a sore thumb is ... Vland/Vland ... when it comes to 1G maneuver drives.
Vland is a Size: 9, Atmosphere: 6, Hydrographics: 7 world ... so a bit of a "super Terra" that is slightly higher gravity (because it's larger).

Out of all the "nearby" worlds on that part of the Vilani Main, only ONE can be seen as being Size: 8+ ... and that's Zhattar/Kasear (at Size: 8).

This means that in the "close abroad" around Vland, the classical J1/1G Free Trader makes perfect sense, since Size: 8+ worlds are most definitely the exception, not the rule. The only place that J1/1G Free Traders would be incapable of landing under their own power within "a decent range" of Vland itself would be at ... Vland itself. For an interstellar merchant ship, that works perfectly fine. You only need to rent orbital shuttle services at the homeworld ... which will have them.

So from a "historical archaeology" perspective, the J1/1G Free Trader is as "lean" an operator as was needed for the region of space within which it originated. It would have to have been constructed in orbit at a highport shipyard at Vland, but then once built such a J1/1G Free Trader would be able to land on and conduct business at 42 of the 44 worlds visible on the above map of just a portion of the Vilani Main, which sounds like a bargain to me!

By "outsourcing" the need to maneuver to a downport on Size: 8+ worlds, you keep the construction costs as low as possible while also keeping the revenue tonnage fraction as high as possible, putting the overall design on a glide path towards profitability that makes the whole venture viable for low end operators to enter the market.

Of course, the classical J1/1G Free Trader still has the pesky problem of needing to buy refined fuel (to avoid misjumps) and the risks of piracy when operating in such a "low drive performance" starship ... but in terms of minimal costs to enter the interstellar trading game, it's hard to do much better than the "ol' rusty bucket" of the J1/1G Free Trader.

So naturally I'm going to have to see if I can "one up" the classical Free Trader design with a "modernized" version that includes a fuel purification plant and a regenerative life support system setup, that also includes a collapsible fuel tank for optional range extension. Might even revise the cargo hold (Cr0 per ton) into being a hangar bay (Cr2000 per ton) so as to enable an option for small craft containerization to enable surface to orbit interface options that way.

The way I already play this is that places like Vland have stations in orbit that belong to various larger corporations and operate at warehouses and docking facilities. Small fry like free traders are contracted by these corps to deliver 'stuff' (a highly technical term) to worlds that have economies that $u#k harder than a vacuum cleaner. They get paid based on the round trip so they make a small profit if they run things smoothly and watch their pennies.

The economic system for this is homebrew and each system is rated. For example, in this system Vland is a 7.93 (out of 10). So, our erstwhile free trader crew would easily pick up their cargo there from the contracted corporation. Trying to get cargo outside of contracting with a company for regular deliveries is nearly impossible on such a world as the companies and corps have a lock on that.
With cargo in hand, you are to deliver it to some loser world nearby and pick up whatever meager scraps are going the other direction. You bring them back and do it again.
You make extra cash and most of your profit off passengers--if any. You can always try your hand at things illegal too.

Trying to just pick up cargos at random from smaller worlds doesn't work. You lose on that big time. There is never enough to make it worthwhile, while operating with a corporation means you get paid at least to a breakeven point.

So, the only time going down on a planet with high G and having a 1 G ship, is when you go to some outlying loser system and that happens to be the main world. Then you can always try to find some outlying colony or settlement on some smaller rock to deliver to and have it shuttled to the main world if that's necessary.

 

[Grav_Moped]

CT anti-gravity provides both lift and propulsion, it's just thrust (like a helicopter rotor). It has to be dimensioned for the amount of thrust it can provide, commonly measured in G of acceleration for the craft.

It's like a helicopter rotor with very limited cyclic control authority -- enough for slow lateral translation, not enough to tilt the rotor shaft. And definitely not enough to enable speeds approaching the retreating-blade-stall limit.

 

[Grav_Moped]

It's an additional drive that would need power concurrently. You would need a bigger PP.

An Air/raft has 4 weeks of continuous operation at (presumably up to) 1.1G, without having a significant fuel or power requirement.

Lifters would only need to operate for long enough to allow landing below stall speed, and takeoff until the point where sufficient aerodynamic lift is available.
Also, only 0.25Gs of additional lift would be necessary, not an additional 1G.

LBB2 includes many components that draw less than 1EP, by definition.

The switch from aerodynamic lift to gravitic lift plus the maneuver drive (and the reverse) is left to artistic license.

 

[Condottiere]

My interpretation is that for Traveller gravitational based propulsion, lifters and thrusters operate differently.

Lifters levitate when they reach local gravity equivalence, and move if they have overlift; potentially.

 

[AnotherDilbert]

It's like a helicopter rotor with very limited cyclic control authority -- enough for slow lateral translation, not enough to tilt the rotor shaft. And definitely not enough to enable speeds approaching the retreating-blade-stall limit.

If you mean thrust vectoring, I have no idea.

I can't recall seeing any mention of grav vehicles being especially clumsy or unmanoeuvrable, nor any mention or how nimble and manoeuvrable they are.

Not being a pilot I assume they need some thrust vectoring to work smoothly, like a helicopter.

 

[AnotherDilbert]

Since it's all house rules, they can work any way you want. I wouldn't make them no cost in either money, tonnage, or power.

An Air/raft has 4 weeks of continuous operation at (presumably up to) 1.1G, without having a significant fuel or power requirement.

"Range in time or distance on a world is effectively unlimited, requiring refueling from a ship's power plant every ten weeks or so."
Effectively unlimited, just like a LBB2'77 power plant:
"A fully fuelled power plant will enable a starship an effectively unlimited number of accelerations (at least 288)..."
It's LBB1-3, it just works, never mind how.

They still require some power or fuel, and from Striker we know how much. A starship would require 100s of MW, not quite insignificant, for me.

Lifters would only need to operate for long enough to allow landing below stall speed, and takeoff until the point where sufficient aerodynamic lift is available.

Why would we bother with aerodynamic lift when we have magical lift, independent of local atmo, air pressure, temperature, composition (humidity), stall speed, and all the other aerodynamic faff?

When we have installed a grav drive, just gently float up until the atmo is basically gone, then accelerate to orbital speed, without turning the hull into a spit roast in a plasma oven?

The air/raft doesn't have wings?

Also, only 0.25Gs of additional lift would be necessary, not an additional 1G.

To handle all cases, with the occasional higher density world, we'd need something like 0.5 G extra lift for VTOL.
0.25 G would give you neutral buoyancy, but no propulsion, on a normal Size A world.

LBB2 includes many components that draw less than 1EP, by definition.

Agreed, but how much?

If you wanted to combine a M-5 drive and a M-1 drive into 6 G capability, T5 style, I would require a PP-6 even if the M-1 uses much less power than the M-5 drive.



Bake the power into the grav system, Fusion Plus or GT power slice style, if you prefer:
Something like:

       Ton    Cost   Power
Grav   1.5     2      0.5
Power  1.5     4.5   -0.5    (LBB5, TL9-12)
=========================
Total  3       6.5    0

Per 1 G per 100 Dton, use as much or little as you want. Think of it as a ½A grav drive?
Round to 3 Dt per "100 Dt thrust", cost MCr 2 per Dt?
Add half a Dt of fuel (or perhaps 5 Dt LBB2 paradigm) if you want it to work continuously for weeks.

Still vastly cheaper than increasing the PP potential on a small LBB2 ship, if that's what's bothering you.

 

[mike wightman]

CT grav modules are null-grav units - that have anti-gravity effects.

In CT A12 we get some additional details on the properties of grav modules

TL8 heavy duty (vehicle) -
Each module costs Cr110,000, weighs 30 kg, and can lift 200 kg against 2G.
Note that these numbers can not be correct.

A 4 tonne air/raft can carry 4 tonnes of cargo for a total of 8 tonnes (I'm ignoring the passengers)

So each grav module has to be producing 2+ tonnes equivalent minimum.

So a TL8 30kg heavy duty module should lift 1,000kg against 2G (not the 200kg the adventure says)

TL12 grav belt 10kg can lift 200kg against 1.5G at a cost of Cr100,000

I have to wonder what a TL12 heavy duty grav module would lift.

 

[AnotherDilbert]

In CT A12 we get some additional details on the properties of grav modules

The LBB3'77 grav module is MCr 1 and produces about 2 tonnes of thrust.
The A12 module is roughly 1/10 of that, so in the same ballpark.
Unfortunately an air/raft doesn't cost several MCr since LBB4 in 1978.


The detailed CT design system for grav vehicles is Striker, published a few years before A12.

Striker grav modules are much cheaper:

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.

So, 2 tonnes of thrust would be 80 kg and kCr 40. Much more in line with an air/raft in LBBs'78+.

 

[Grav_Moped]

If you mean thrust vectoring, I have no idea.

I can't recall seeing any mention of grav vehicles being especially clumsy or unmanoeuvrable, nor any mention or how nimble and manoeuvrable they are.

Not being a pilot I assume they need some thrust vectoring to work smoothly, like a helicopter.

It's not about maneuverability per se, it's about the ability to tilt the thrust axis significantly away from vertical.

 

[Grav_Moped]

Why would we bother with aerodynamic lift when we have magical lift, independent of local atmo, air pressure, temperature, composition (humidity), stall speed, and all the other aerodynamic faff?

When we have installed a grav drive, just gently float up until the atmo is basically gone, then accelerate to orbital speed, without turning the hull into a spit roast in a plasma oven?

The air/raft doesn't have wings?

Because it's cheaper and doesn't require doubling the size of the power plant and its minimum fuel requirement to add the extra margin of lift needed to get off the ground?

 

[AnotherDilbert]

It's not about maneuverability per se, it's about the ability to tilt the thrust axis significantly away from vertical.

So, thrust vectoring?

It doesn't say directly, so we have to look for secondary hints, e.g. manoeuvrability or the lack of it.

A normal 1.1 G air/raft would be able to use 1 G lift (down) and 0.1 G propulsion (rearwards).
In 0.5 G gravity it would be able to use 0.5 G lift (down) and 0.6 G propulsion (rearwards).
That seems to suggest that it can change the trust vector quite a lot?

 

[AnotherDilbert]

Because it's cheaper and doesn't require doubling the size of the power plant and its minimum fuel requirement to add the extra margin of lift needed to get off the ground?

Then why both, select one or the other?

 

[Condottiere]

It occurs to me that if you have a tail sitter, thrust vectoring becomes less of an issue.

 

[mike wightman]

True, but you would definitely be reliant on thrust being greater than weight.