Using Traveller ships and deck plans for ships with reaction drives

[mike wightman]

For a TL9 pre jump solar system campaign I ran a long time ago I repurposed the drives.

The jump drive and jump fuel became the long range in-system reaction drive - g rating of 0.2-1.2 (multiply the jump rating by 0.2) with jump fuel being reaction mass providing a number of days of continuous burn - 10% per 0.2g/day.

The pp remained as is but with pp fuel removed, the mdrive became the combat drive that provides 1-6g of thrust but uses fuel at a much faster rate.

I used some of the Traveller deckplans - the x-boat, x-boat tender, the AHL - but also used the old Star Frontiers ship deck plans since they are all tail sitters.

 

[Ulsyus]

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.

I crunched some numbers on a ship-based campaign once and found that a number of the systems my players travelled to or transited through had jump-limits within the orbit of gas giants. I don't think that we can presume that stopping at a GG in a system will always be an easier option than burning to a high or low starport.

 

[Ulsyus]

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.

Had you thought of adding antimatter into the mix to get more bang for, er, gram?

Winchell has rigour in his work, but Kammash and Galbraith have some maths that's a bit beyond me though the whole thing is a nice read.

I do like their comment

In the interest of safe space travel and physical welfare of the crew

Such considerate young men.

 

[whartung]

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....

Actually, Chadwick now thinks the HEPlaR were too conservative, and that modern Fusion drives can actually be much more efficient.

 

[Brandon C]

Actually, Chadwick now thinks the HEPlaR were too conservative, and that modern Fusion drives can actually be much more efficient.

mumbleEpsteindrivemumble

 

[Thot]

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.

Sure, but I don't want to do that.

 

[Thot]

Had you thought of adding antimatter into the mix to get more bang for, er, gram?
[...]

The problem here is that giving nuclear-level weapons in the hands of regular people will cause irregular results, so I'll just stick with an electric propulsion. 120 km/s as my exhaust velocity is actually sufficient for what I need, and that is not all that implausible.

Sure, 2 GW is a 1970s nuclear power plant, not ship-sized (a Nimitz class aircraft carrier has just under 200 MW), but more efficiency there is more easily justified than magically replenishing reaction mass.

 

[Thot]

So your end result is 2Gs for 7 days?

No, 2G for 600 seconds. There was an error stemming from unit conversions in my spreadsheet.

 

[ShawnDriscoll]

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?

High-tech worlds that prefer such engines always make for interesting encounters.

 

[whulorigan]

The problem here is that giving nuclear-level weapons in the hands of regular people will cause irregular results, so I'll just stick with an electric propulsion. 120 km/s as my exhaust velocity is actually sufficient for what I need, and that is not all that implausible.

It doesn't have to be a nuclear-level weapon. One of the proposed future propulsion systems on NASA's drawing board is known as an Antimatter Thermal Rocket (ATR). Similar in propulsive principle to a Nuclear Thermal Rocket (NTR), the ATR replaces the fission (or fusion) reactor that heats the reaction mass with a unit that produces antimatter in microscopic quantities that is then injected into the reaction plasma, causing it to be heated and increasing its exhaust velocity.

 

[Carlobrand]

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 little reason an X-boat wouldn't be J-6 as soon as that drive is developed irrespective of jump fuel usage. Speed of communication is too vital in an Imperium as large as this one.

...
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 ...

"Considerable space activity" implies a population and infrastructure capable of doing it. In that system, Nathan's point is apt: if the infrastructure is in place, is it worth your while to go anywhere besides the mainworld? Not unless they've erected the infrastructure to encourage that as well, or unless you have some goal that can best be satisfied by going "off-road". Otherwise you're spending time and fuel basically to replace the fuel you just expended, and the more time and fuel you expend to get to the free fuel, the less cost-efficient it becomes.

Where that population and infrastructure are lacking, and where there are not conveniently obvious alternative sources of fuel, you're probably going to buy old scouting reports that tell you where the ice is - and then you expect some mining company has claimed it and is charging fees to anyone who wants to come and get it. It's a good bet some of those low pop worlds are families or communities gathered around the best fuel source in the system and making a bit of extra money selling it and a few drinks to passing ships. Easier to do business with them than to have to clear your filters every 15 minutes trying to draw fuel from swamp water.

 

[Thot]

It doesn't have to be a nuclear-level weapon. One of the proposed future propulsion systems on NASA's drawing board is known as an Antimatter Thermal Rocket (ATR). Similar in propulsive principle to a Nuclear Thermal Rocket (NTR), the ATR replaces the fission (or fusion) reactor that heats the reaction mass with a unit that produces antimatter in microscopic quantities that is then injected into the reaction plasma, causing it to be heated and increasing its exhaust velocity.

The antimatter itself is the weapon, regardless of how it is supposed to be used.

 

[Thot]

No, 2G for 600 seconds. There was an error stemming from unit conversions in my spreadsheet.

I should add that my jump drive will not require the canonical 100 diameter limit, but merely a small safe distance (something like a few ten thousand kilometers) from any planetary bodies, so 12 km/s for 10% of the ship's mass is perfectly fine in that context.

 

[Thot]

Sigh. Its all nonsense, because I miscomputed the energy requirement, too. It's a thousand tiimes as much, meaning too much.

I could operate a ship that has an acceleration of 2 cm/s² that way, but such a vessel would never be able to take off.

There's a reason Traveller assumes gravitic technology...

 

[whulorigan]

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Sigh. Its all nonsense, because I miscomputed the energy requirement, too. It's a thousand tiimes as much, meaning too much.

I could operate a ship that has an acceleration of 2 cm/s² that way, but such a vessel would never be able to take off.

There's a reason Traveller assumes gravitic technology...

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You could always have some kind of understanding of gravity that only allows the partial screening of the gravitational interaction (i.e. Partial Contragravity - enough to allow easier take-off by conventional means, but not necessarily enough to allow total weightlessness or allow maneuver).

 

[Thot]

Hm. Maybe I could use a system like this:

http://www.thedrive.com/the-war-zone/5380/air-force-eyes-air-breathing-rocket-plane-mothership

That is, a ship that uses athmospheric oxygen in addition to brought-along hyrdrogen, to save weight.

Or by extension, an electric propulsion that uses the atmosphere as reaction mass for take-off, and the fuel in the tanks only once in space... where the acceleration and delta-v will be much more limited.

 

[Chaos]

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You could always have some kind of understanding of gravity that only allows the partial screening of the gravitational interaction (i.e. Partial Contragravity - enough to allow easier take-off by conventional means, but not necessarily enough to allow total weightlessness or allow maneuver).

How about gravity drive only works within a gravity well? Say it´s some sort of handwavium doohickey that doesn´t actually generate gravity as such, but counteracts an external gravity source, either reducing it (to allow descent and safe landing) or even negating it (for take-off and boost to orbit) - but far away from major celestial bodies, without a source of gravity to manipulate, it won´t work at all?

 

[whulorigan]

How about gravity drive only works within a gravity well? Say it´s some sort of handwavium doohickey that doesn´t actually generate gravity as such, but counteracts an external gravity source, either reducing it (to allow descent and safe landing) or even negating it (for take-off and boost to orbit) - but far away from major celestial bodies, without a source of gravity to manipulate, it won´t work at all?

Actually that was my point, though perhaps I didn't state it clearly. And my additional observation was that such a form of "contragravity" need not even necessarily screen all gravity, but perhaps only a fraction (perhaps weight is lessened by 30%, or 60%, etc).

 

[Brandon C]

How about gravity drive only works within a gravity well? Say it´s some sort of handwavium doohickey that doesn´t actually generate gravity as such, but counteracts an external gravity source, either reducing it (to allow descent and safe landing) or even negating it (for take-off and boost to orbit) - but far away from major celestial bodies, without a source of gravity to manipulate, it won´t work at all?

And the drop-off for thrust/lift of the grav drive could be severe -- for every doubling from optimum range (1000 km? 100 km?) thrust/lift is divided by four. So, at 8x range lift is 1/64th rated.

 

[Chaos]

And the drop-off for thrust/lift of the grav drive could be severe -- for every doubling from optimum range (1000 km? 100 km?) thrust/lift is divided by four. So, at 8x range lift is 1/64th rated.

Gravity diminishes with the square of distance. So, yeah.