An Ode to Simplicity

Simplicity, which by and large we had with classic Traveller's initial little black books (LBBs), is hard to overvalue.  In attempting to achieve the goal of injecting more realism into a hard science fiction version of a Traveller based setting, it is extremely easy to forget this.  Complexity is alluring to some of us, Striker and later, Fire Fusion and Steel, gave us complexity in spades all in the name of realism.  However, as much fun as it can be to mess around with those complex systems, they really don't do much if anything for role playing sessions.  Which is, I think, kind of important for a role playing game.

High Guard gave us what to me is an upper bounds on desirable complexity, still some GM's believe it to be a bit too complex and favor the simpler LBB 2 starship construction rules.  So for construction rules at least, we have examples of workable, usable, upper and lower bounds on complexity.  It isn't an easy target to aim for, let alone hit, when pursuing 'hard science'.

The same considerations hold true for combat systems.  Various Traveller products and adaptions of similar rule sets from other games have given us combat systems that span the range of abstraction levels and the scales of single ship to multiple fleet battles.  Odd thing is, I can't remember, in all my years of role play gaming, ever needing to handle more than small scale battles of a few ships at most in a session and then my players and I were quite satisfied with a more abstract model of movement at least.  More complexity just slows down play, whereas simplicity makes for more enjoyable, interactive, reasonably fast paced gaming sessions.

The same considerations once again hold true for many of us when it comes to skill systems and task resolution systems.  Every time my players and I tried using more detailed skill trees and formally structured task resolution systems, the sessions bogged down into periods of searching through books for skill descriptions, rules lawyering over task resolution, and quickly became roll rather than role playing.  Classic Traveller's LBBs give a good basic set of skills and a minimal set of rules that work quite well.  Nice and simple.  The hardest part seems to be players and GMs coming from other gaming systems that are overly complex and feel lost without all that legal structure.  In the final analysis, once again, simplicity makes for a better game.

This topic has arisen for me because of another game I play.  An open source game, its current crop of developers decided to make combat more realistic.  In the process they've completely broken it and now need an entire new set of additions to get back to the same level of functionality we had in previous versions.  The blind pursuit of realism should never get in the way of the playability and enjoyment of a game.  Seems obvious, but it is a very easy misstep to make when navigating the narrow and rocky trails of game design.

So what does this all mean for the Dark Stars ATU?  Well, once again I find myself waffling.  By throwing out the civilization model underlying Traveller, I can make a playable setting that meets the hard science with one exception criteria.  The problem is that in doing that I've just thrown out half or more  of that body of work we call Traveller.  In the abstract, it works and is quite doable, in reality it bogs down into needing a ton of detail work before it is remotely useable.

In an attempt to avoid the plunge headfirst into a man year or more of background and detail work, I am left with trying to find another solution to the wilderness scenario that meets the hard science with one exception criteria.  As much as I hate it, the process is bringing me back around to giving serious consideration to some form of 'gravitics' pseudo-science.  I really don't like that approach though.  While it solves some problems it introduces myriad others and is at the bare edge of plausibility to qualify as anything remotely hard science fiction.

So I found myself reading about fringe science like the Heim-Droscher hyper-drive.  If you've read much of my ramblings elsewhere on this blog you no doubt realize that I'm a layman when it comes to physics, somewhere around early to mid college level of knowledge - a bit further advanced with mathematics possibly, but I like reading about physics, especially quantum physics.  In the process I've come to discover that our blind faith in Einstein is a little bit misplaced, special relativity shows some fraying around the edges so to speak.  There are other theories.

Yeah yeah I've now lost all credibility with the loyal Einstein is holy camp.  I'll let you in on a little secret, most of them don't understand physics either.  In fact, no one does.  What we have is a collection of theories that fit most observed data within certain error limits.  Quantum physics is bringing everything we think we know into question.

So what does this mean from a science fiction perspective?  Well, for starters it seems a bad idea to tie your shirt-tails to a fringe theory.  Next year someone finally disproves the theory and there you sit looking like yet another casualty of technological progress.  The best advice I've ever read on the subject is to concentrate on the effects rather than the cause.  Say as little about the cause as you can get away with - you'll stay relevant longer and don't immediately set yourself up to be ridiculed by pessimistic no-space-ever fanatics.

Looking once again, hopefully with newly refreshed eyes, at the wilderness scenario (without re-imagining civilization)  we can enumerate the effects of our mysterious scientific advance.

1. It allows for cheap surface to low orbit.
2. It allows for sustained 10 m/s^2 acceleration sufficient for round trips from orbit to ftl point.
3. It allows some form of ftl.
4. The total round trip times for the wilderness scenario closely matches classic Traveller.

I'm tempted to add a fifth element although it isn't an effect, rather the fifth element would be an attributable cause that sounds plausible, can't be easily disproved, and doesn't break proven physics.

In order to address the effects seriously, it is necessary to define point 3 further.  Just what form of ftl are we going to allow?  I'm biased towards the general Alderson Point idea as I think the stock Traveller jump space ftl just opens up too many cans of worms to address with hard(er) science.  In order to address point 4, we need to also define the average normal space trip time under the constraint of point 2 between low orbit and the ftl points.  If we consider the jump points to be non orbiting locations ala Alderson Points, then we need to find the average distance between the average planetary orbit and the average jump point location.

Using the original Lares point/region idea for the first guess at jump point locations places them roughly 0.63 AU from Sol in our solar system assuming a 0.015 m/s^2 gravity threshold.  Assuming we don't want to get closer to the star than absolutely necessary, our maximum travel distance between ftl points becomes just under 2 AU giving an average of 1 AU (keeping things simple) between ftl points.  This works out to a bit over 3 days travel at 10 m/s^2 sustained acceleration.  Our average distance from LEO to Lares point works out to about the same, maybe a hair longer.  Let's call our average wilderness scenario surface to ftl point a 3.5 day jaunt.   Now in stock Traveller each one-way section of the wilderness scenario takes roughly 8 days, so in answering point 4 we need to give our ftl method a transit time of 1 day between systems.   We're back to Lares drive specs again.

Now for the 'fun' part.  Assume for a moment that our maneuver drive is a reaction drive and that 50% of a vessel's mass in fuel will get us through one entire leg of the wilderness scenario.  Now we need a total delta-V of... yikes!  6x10^6 m/s... requiring an Isp of only a bit under 900k.  This is a bit of a problem since it is higher than the maximum possible Isp theoretically achievable with magnetic containment fusion.  That figure is without regards to efficiency loss and material capabilities which serve to limit achievable Isp's to far lower figures.  Congratulations, we've just reinvented HEPlaR.

Hmm.. try for a middle ground?  Abandon the fixed point ftl idea and assume something remotely resembling stock Traveller jump drives but with a lower gravity gradient, say 0.005 m/s^2.  This means that for Earth, Sol's gravity well predominates and the distance to jump point is roughly 13.3mkm distance.  This is about 64 hours constant thrust at 1m/s^2 (assuming midpoint turnaround).  Now we need a much more modest delta-V of around 500000.  Given our desired fuel load, we can get away with an Isp of 66.5k.   While we're now an order of magnitude below theoretical maximums, we're still about two orders of magnitude beyond current projected designs.

We're also neglecting for now the surface to LEO special requirements, but at least we are in the general ballpark with this most recent model.  Our Isp requirements are about twice that of the projected maximums for VASMIR and some pulse fusion theoretical designs.  We also may, however, be too dependent upon the specifics of our solar system for the distances to remain in the ballpark.

Let's aim for a more planetary dependent ftl point distance equation, the catch here is, basing on gravitational gradient, we require a threshold greater than 0.00593 m/s^2, otherwise in our solar system the sun's gravity would predominate.  A threshold of 0.01 m/s^2 works out to just under 200,000 km.  Even at a low constant acceleration of 1 m/s^2 this is only an 8 hour flight from low orbit.  A catch with this is that now surface to LEO delta-V is no longer negligible so our total delta-V requirement is  about 78000m/s, with our desired fuel load we get an Isp requirement of around 11,500.  Ignoring the necessary high thrust component for surface to LEO for a moment, this is comfortably within range of projected technologies and efficiencies.

There are a couple serious problems with this last scenario, it is quite possible that ships would be able to launch ordinance at planetary targets immediately upon exit from ftl for one.  Another is that space battles are, at best, confined to low orbit by the time you make intercept.  Note that the ftl threshold with this last scenario is well inside the Moon's orbit.

When you consider hard science, the ftl threshold parameters get very dicey for any commonly applicable value to yield near habitable planet entry and exit points.  Either you end up entirely too close to the planet for any kind of space battle, or else the entry and exit points are highly dependent upon the nature of the solar system. So, round robin style, we're back to looking yet again at the first scenario with fixed ftl points - dizzy yet?

With reasonable fixed ftl points, we're stuck with either HEPlaR like drives that even with a bit of handwavium break physics, or lengthening the transit times.  Let's take a look at doubling the time first.  We'll make our ftl transits instantaneous and allow a full week each way between average ftl point and average habitable planet.  Using the 1 AU ballpark figure, we need a constant acceleration of, well lets call it 2 m/s^2.  This gives an Isp requirement of around 350000, still pretty hefty but within 3He/2H fusion range.  Up till now we've been ignoring the thrust requirement and have been looking just at the Isp.  Even a measly 0.2g of thrust at these high Isp levels is, quite frankly, impossible given physics as we know it.  It doesn't break physics to have such a device, but no one has a clue how to create one.  Temperature levels are extreme using any straight up design even if all other engineering factors were accounted for.

Just for fun, lets double the time again.  Two weeks each way.  Now we can get by with 0.5 m/s^2 constant acceleration and an Isp requirement of about 175000.  This makes 3He/2H fusion look a bit more realistic but doesn't open any new doors.  Doubling again to a month each way, we get by with 0.1 m/s^2 constant acceleration, and an Isp requirement of around 70000.  Ignoring the 'bang bang' engines due to manufactured fuel pellet requirements, while this doesn't open any particularly new doors for us it is interesting that we're just a little over twice the Isp of a magnetoplasmadynamic (MPD or VASIMR) drive. 

I started off with observations about the value of simplicity and then proceeded to dive into complexities.  Mike Wightman over on the CotI forums briefly explained a simple system he had used in a reply on my Dark Stars ATU thread.  Basically he used the High Guard jump drive percentages as the maneuver drive percentage with maneuver ratings in m/s^2 rather than standard gravities.  He then used the jump drive fuel requirements as the G-hour fuel requirements.  I'd like to end up with something nearly as simple for the deep space maneuver drives in the mass based design system.

To start with, a base engine mass of 1% of ship's wet mass per tenth of a meter per second squared of acceleration works fine as high Isp engines generally have a poor thrust to mass ratio.  After examining all the above breakpoints, I like the fixed ftl points of the original Lares idea along with a full week's travel time average.  The Isp figure of 180000 works out to 0.2 tons of fuel per hour per meter per second squared of acceleration.  In other words, each G hour requires 2% of the ship's mass.  This isn't quite correct, but it is fairly close and it is simple.  Note that this is 5x the efficiency of Mike's approach but is necessary for the travel distances and times involved.

Just to check here, the 180000 Isp with a fuel ratio of 1:1 gives a total delta-V of roughly 2,600 km/s and a constant acceleration range of 1.3 AU per leg (x2).  I'm definitely hacking the math here!  Even so, its pretty spot on to the requirements.  Time is 14.4 days and acceleration 0.5m/s^2.

When it comes to realistic reaction drives usable in a Traveller setting, this is about as close and simple as I can get.  Some tables are still needed for various delta-V costs and times for distances at different accelerations to get rid of the hairy math but that's for the future.

Honestly I'm still not satisfied, the changes in travel times are too large and would require a serious adjustment of pricing for goods, services, transport, the ships themselves, etc.