Using Traveller ships and deck plans for ships with reaction drives

[Thot]

I have an idea about a campaign I might be running - one with actual Newtonian spaceships. Given the enormous treasure of Traveller deck plans I own, and the fact that they all set aside vast amounts of internal space for fuel, I figured this should be possible:

A Jump-1-Ship in Traveller will have 10% of its volume (and as a gross simplification, also 10% of its mass) available as fuel (I think I will use water) for the reaction drive. I played around with the numbers a bit, and found out that, in order to reach escape velocity (and then some) with that amount of fuel, I'll need an exhaust velocity (so a delta V of around 12 km/s) of the rocket of 120 km/s, which is the upper range of what is given in public sources for the VASIMR ion drive. (Of course I won't use VASIMR, but some kind of electric propulsion it is). A 1,000 ton-ship would need something like a 2GW reactor for that with an acceleration of 20m/s², which should be doable with some good compact advanced fission reactor.

The longer the campaign lasts, the more ships they will encounter, so

Anything I should think about when trying this?

 

[flykiller]

Anything I should think about when trying this?

likely no-one will want this anywhere near populated areas, so groundside starports will be in deserts or on oceans and will have associated transport systems between landing zones and population.

 

[kilemall]

Well, as I understand it that the TNE Traveller version went HEPLAR and had a maneuver fuel system with limited burns.

An interesting direction suggested by your wording might be looking into reversing jump and maneuver fuel use.

 

[Nathan Brazil]

If you declare that both Jump and the Reaction use regular hydrogen, could you not simply use the same tank(s) and call it a day? This would not change too many things then for deck plans, but your worlds might be different.

The biggest one would be making the call of going to gas giants or not to refuel, like is it worth my time and effort to burn my way to one with full tanks on the way out and increased vulnerability on the way in. People might just refuel on the way in.

Same decisions about systems without gas giants. If the system does not have one, is it worth your while to go anywhere besides the mainworld especially if there is no water in the system or in YTU you do not allow reprocesing using water?

In a similar thought, systems with no gas giants and no water on the regular planets, consider the effort of getting them from the Oort cloud amd what those system UWP would be like. Perhaps too hard to be inhabited normally. Compared to YTU with standard drives anyways.

Just some thoughts on the impact of reaction drives.

 

[Barrel]

It seems to me that using reaction drives drastically changes the flavor of the game (just one of many things I didn't like about TNE). Instead of just calculating travel time for a given acceleration, delta-vee is very limited, and the first calculation must be if a given trip is possible without taking months. I'm not saying this might not be an enjoyable campaign, just very different than most.

 

[Brandon C]

What you want does seem a lot like a more efficient HEPLaR drive, which is already highly efficient. If you cut jump fuel requirements in half, you have plenty of room for reaction mass without making other changes. I do agree that everything should use the same kind of fuel for simplicity.

I also suggest you drop the 6G limit, but instead use the maneuver drive TL progression as a limit on artificial grav compensation -- a TL9 ship couldpull 30Gs for hours but the crew would be dead in minutes.

 

[aramis]

Well, as I understand it that the TNE Traveller version went HEPLAR and had a maneuver fuel system with limited burns.

An interesting direction suggested by your wording might be looking into reversing jump and maneuver fuel use.

HEPlaR had issues with the requisite fuel velocities being orders of magnitude higher than sanity... essentially, low grade PA weapons... and being used on air/rafts....

As in, the drive on the air raft should induce cancer in someone standing within 30m behind on in operation... as they get hit with a full body cascade of alpha and beta, plus the secondary from that hitting atmosphere... if it doesn't cook them first, because it's doing more than 3,000km/s...

 

[Brandon C]

HEPlaR had issues with the requisite fuel velocities being orders of magnitude higher than sanity... essentially, low grade PA weapons... and being used on air/rafts....

I still find it easier to handwave that than reactionless drives.

 

[Thot]

If you declare that both Jump and the Reaction use regular hydrogen, could you not simply use the same tank(s) and call it a day? This would not change too many things then for deck plans, but your worlds might be different.

My plan is even more radical: Jump will not require fuel at all, just energy (drawn from fission or fusion) and time to spin up the drive. Water as reaction mass just has the advantage that it is rather heavy (making it more volume-efficient than hydrogen) and should be easy to get everywhere. So I should have plenty of reaction mass for my reaction drives.

I vagueley remember TNE's reacion drives... does anyone know what their exhaust velocity was?

 

[Thot]

It seems to me that using reaction drives drastically changes the flavor of the game (just one of many things I didn't like about TNE). Instead of just calculating travel time for a given acceleration, delta-vee is very limited, and the first calculation must be if a given trip is possible without taking months. I'm not saying this might not be an enjoyable campaign, just very different than most.

That is kind of my intention, yes. A ship with 10% of its mass as fuel will be able to take off from exactly one Earth-sized planet, jump somewhere, land there, and will then have to refuel. Ships with higher percentages will, of course, be slightly better off.

 

[Brandon C]

That is kind of my intention, yes. A ship with 10% of its mass as fuel will be able to take off from exactly one Earth-sized planet, jump somewhere, land there, and will then have to refuel. Ships with higher percentages will, of course, be slightly better off.

So that works out to about 12-14 hours of thrust at 1G (depending on how much reserve reaction mass you want) based on a quick scan of a table in MgT (Book 6: Scoundrels). In MgT, it's generic reaction drive would require up to 35% of the ship's mass/volume for that many hours of thrust (2.5% x hull volume x G hour). Your target seems to be around 0.75%.

 

[Thot]

So that works out to about 12-14 hours of thrust at 1G (depending on how much reserve reaction mass you want) based on a quick scan of a table in MgT (Book 6: Scoundrels). In MgT, it's generic reaction drive would require up to 35% of the ship's mass/volume for that many hours of thrust (2.5% x hull volume x G hour). Your target seems to be around 0.75%.

My own computation:

Exhaust velocity: 120.000,00 m/s
Assumed Acceleration:20,00 m/s²
Mass of ship: 1.000.000,00 kg
Reaction mass share (water): 10,00%
Reaction mass thus: 100.000,00 kg
Exhaust per second: 0,17 kg
Maximum burn duratIon thus: 600.000,00 seconds (roughly 167 hours)
Raw energy requirement (assuming 100% efficiency, as per 1/2m*v²): 1,200,000,000.00 W (1,200 MW; as we more likely have something like 60-80% efficiency, we round this up to 2 GW)
This would require a fission reactor of this mass (according to GURPS Traveller Interstellar Wars; I used this just as a general ballpark check to see if its pluasible): 150,000.00 kg (or maybe 300,000 kg including the inefficiencies)

 

[Thot]

Slight error, heh. Exhaust per second is 1000 times that, so we have 600 seconds of burn duration at roughly 20m/s², for a delta V of 12km/s. I knew something was off there...

 

[Brandon C]

My own computation:

Exhaust velocity: 120.000,00 m/s
Assumed Acceleration:20,00 m/s²
Mass of ship: 1.000.000,00 kg
Reaction mass share (water): 10,00%
Reaction mass thus: 100.000,00 kg
Exhaust per second: 0,17 kg
Maximum burn duratIon thus: 600.000,00 seconds (roughly 167 hours)
Raw energy requirement (assuming 100% efficiency, as per 1/2m*v²): 1,200,000,000.00 W (1,200 MW; as we more likely have something like 60-80% efficiency, we round this up to 2 GW)
This would require a fission reactor of this mass (according to GURPS Traveller Interstellar Wars; I used this just as a general ballpark check to see if its pluasible): 150,000.00 kg (or maybe 300,000 kg including the inefficiencies)

So your end result is 2Gs for 7 days?

 

[kilemall]

HEPlaR had issues with the requisite fuel velocities being orders of magnitude higher than sanity... essentially, low grade PA weapons... and being used on air/rafts....

As in, the drive on the air raft should induce cancer in someone standing within 30m behind on in operation... as they get hit with a full body cascade of alpha and beta, plus the secondary from that hitting atmosphere... if it doesn't cook them first, because it's doing more than 3,000km/s...

I've gone with the accelerator drive for my reaction engines but with two alterations to get around the irradiating everything problem-

1. During liftoff the engines go to classic pure burn mode, firing on pure fuel and temporarily generating double the Gs. This only lasts 100-200 seconds, after which the ship is risking damage and prodigious fuel use.
2. My bdddy particle the muon comes to the rescue- since it's induced to exist just long enough to provide reaction mass, I have to have that much less mass to accelerate against and thus less overall radiation.

As for anti-grav, don't feel the need to replace/disallow it, so no need to put any reaction on them for thrust, IMTU I even allow mixing grav and reaction on ships and some planets only allow grav landers for ecological safety purposes.



But anti-grav is just not practical for those deep space trips.

 

[kilemall]

A further thought on flipping maneuver and jump fuel usage- it would make for a much more logical ship design to function paradigm.

So an X-boat could use relatively minuscule fuel for it's J-4 and possibly pull several jumps before service/refueling.

A commercial ship could spec J-3 and M-1 and have a lot more cargo space for those longer/'faster' jumps, or at least be closer to free trader percentage carry opportunity.

A warship at M-6 would be mostly fuel, with little of the commercial cost or operations concerns, and strategically could make several jumps without refueling but greatly reduce tactical maneuver options.

 

[Brandon C]

I think you should simplify the math: one ton of drive provides X tons of thrust and requires Y tons of reaction mass per G-hour. For most versions of Traveller, you really don't need more detail than that.

 

[Carlobrand]

If you declare that both Jump and the Reaction use regular hydrogen, could you not simply use the same tank(s) and call it a day? This would not change too many things then for deck plans, but your worlds might be different.

The biggest one would be making the call of going to gas giants or not to refuel, like is it worth my time and effort to burn my way to one with full tanks on the way out and increased vulnerability on the way in. People might just refuel on the way in.

Same decisions about systems without gas giants. If the system does not have one, is it worth your while to go anywhere besides the mainworld especially if there is no water in the system or in YTU you do not allow reprocesing using water?

In a similar thought, systems with no gas giants and no water on the regular planets, consider the effort of getting them from the Oort cloud amd what those system UWP would be like. Perhaps too hard to be inhabited normally. Compared to YTU with standard drives anyways.

Just some thoughts on the impact of reaction drives.

There is pretty much always water in a system. Finding it and getting to it, using reaction drives with limited burns, that's where the headaches start.

 

[Chaos]

So an X-boat could use relatively minuscule fuel for it's J-4 and possibly pull several jumps before service/refueling.

Actually, there´s little reason an X-boat wouldn´t be J-6 as soon as that drive is developed, if jump fuel usage is no longer the constraining factor.

There is pretty much always water in a system. Finding it and getting to it, using reaction drives with limited burns, that's where the headaches start.

I think in systems where the water isn´t conveniently located, there´d be considerable space activity involved in getting the water to where it is needed - harvesting gas giant ring material or mining ice asteroids, then giving a the resulting ice chunks a slight nudge to where they´re needed.

Limited burns aren´t a problem if the object doesn´t need to arrive in a timely fashion. If a chunk of ice takes a year or two to arrive in the vicinity of the mainworld, so what? The ice you need right now has already been sent on its way a year or two ago and is just about to arrive.

 

[Brandon C]

You know, if you are keeping contragravity, a streamlined ship can get by with a lot less thrust than you are using. It can simply fly into space, it doesn't have to blast off like a rocket.