Lightbulb on... Nuclear Lightbulb!

So I've been working on the spacecraft design sequences and after getting hulls, configurations, various forms of streamlining and materials into rough shape I decided to tackle maneuver drives.   After trotting out the various theoretical specs and driving myself to drink (coffee- lots of coffee), I realized that I, like perhaps many other Traveller players, had become so used to the gravitics and nuclear dampener technology handwaviums that I had been totally overlooking something.

Fuel!  We Travellers take it for granted that we can just scoop up unrefined fuel anywhere, any old junk and feed it into our power plants, though maybe not our jump drives without a second thought.  Well... when I started seriously examining the various forms of relatively realistic nuclear reaction drives I started seeing all sorts of different fuel requirements and operating condition gotcha's.  Plain old hydrogen might be easy to come by, deuterium basically just needs a simple fuel extraction/purification process, tritium and helium-3 on the other hand isn't something you're going to find easy.  At least not out in the wilds anyhow.

Fuel isn't a problem with realistic nuclear power plants, whether fission or fusion, as they can easily carry a years worth of fuel built in to the reactor.  Refueling them is part of annual maintenance.   Nuclear fusion drives are an entirely different kettle of fish since they waste quite a bit of their fuel going out the nozzle as superheated plasma.  The inertial confinement fusion drives are even worse since they need specially prepackaged fuel pellets containing a deuterium/tritium mix.

On top of the wilderness refueling issues, there is the environmental friendliness, or rather the lack thereof, issue.  Realistic nuclear fusion drives are as bad as nuclear thermal reaction drives for spreading radiation around.  Not quite as bad as open gas core fission or an Orion bomb pumped drive but definitely unfriendly to the neighbors!

There is pretty much only one nuclear drive that is environmentally friendly (other than the scorched spots), that is the closed gas core nuclear thermal reaction drive - commonly called a nuclear lightbulb drive.  It isn't as efficient as other NTR types but it looks like it may be possible to get a thrust to weight ratio greater than one so it's almost good enough theoretically for surface to orbit.  As I was looking at the nuclear lightbulb design and specs, I remembered something about a way to boost the thrust of a NTR at the expense of its Isp.

With a solid NTR, it is possible to inject liquid oxygen into the throat of the thrust nozzle and gain a factor of 3 or so in thrust output at the expensive of exhaust velocity.  The design is called a LANTR drive with the LOX acting as a sort of an afterburner giving a reverse scramjet mode.  Well, since lightbulbs and solid NTRs have the same preferred reaction mass (H2), what works for one might work for the other, right?  Sort of, maybe, kinda.. *if* it would work, I expect you'd see less of a positive effect than with a LANTR and more of the negative side-effects.  Perhaps doubling thrust at a fairly steep Isp penalty.

Another nice synergistic benefit of a LACGCNTR is shared with LANTR and that is the H2 and LOX fuel is quite usable in chemical rockets and multimode scramjets as well.  Nice for booster engines and small craft, even vehicles.

The more the picture shapes up, the more the following idea seems to emerge: a small to medium sized airframe streamlined starship with a LOX boosted Nuclear Lightbulb reaction drive.  Go most anywhere and still have easy wilderness refueling even without gravitics and nuclear dampener technologies.  A bit slower maybe, but isn't that what fast-drug is for?

Until next time,
Omnivore

Since writing the above I've been examining numerous NTR designs and the rather large number of interesting modified variants.  Bimodel, Trimodel, almost called my idea the Quadmodel but sounded too much like Quasimodo, and then I came up with yet another addition to my hybrid NTR from hell and am at a loss for an official sounding name for what I've been calling the Frankenstein NTR.

The Frankenstein NTR recipe: take one Pratt & Whitney Triton NTR, mix with a Plus Ultra Hybrid Electro-Thermal MITEE, change the reactor core to a closed gas cycle NASA design, and paste the back half of a VASIMR like Magnetoplasmadynamic drive in place of the nozzle.  Oh and almost forgot, add in a scramjet intake as an alternative to the LOX injectors.

After more reading and research, it turns out the closed gas cycle idea is pretty problem filled, the impact of modern chaos theory as applied to gas movement kinda puts the kabosh on a central innovation in the design.  I thought that perhaps I'd found a workaround in the molten salt fueled reactor designs but the temperatures are too low.  That's the bad news.

The good news is, a molten salt fueled thorium reactor core might well solve some of the same problems the closed gas core solved but without the melt down problems.  Of course, without the Isp boost too but can't have everything.  On another front, both scramjet and plasma drive afterburner configurations seem to be quite possible.  So the Frankenstein NTR may yet live, though at half the Isp.

Overview of Dark Stars Traveller

What is it? 

Dark Stars Traveller is an ATU (Alternate Traveller Universe) intended for use with the Traveller Role Playing Game.

What is the difference between the Dark Stars ATU and the official Traveller universe (OTU)?

While I've enjoyed Traveller and the OTU over many years, I've always had a yearning for hard science fiction.  All apologies aside, the Traveller OTU is far from hard science fiction.  In the Dark Stars ATU, every technology used has a firm basis in current theory with only one exception.  The exception, and one I feel is necessary for the type of game I want to have and play, is a form of faster than light travel.  Even in the exception, I've done my best to keep it from absolutely breaking known physics.

What is the overall background of the Dark Stars ATU?

Dark Stars is set over 25000 Terran years in the future.  Mankind has spread far and wide but has suffered through periodic rises and falls of imperial ambitions.  Nearly all of the oldest civilizations have been lost in time, Earth itself is either forgotten or considered a legendary myth.  The remnants of humanity are once again climbing out of darkness to claim a place in the stars.

In Traveller terms, the overall setting is very similar to a post 3rd Imperium Hard Times/One Small Step crossed with a bit of cyberpunk/transhumanism.  The absence of gravitic technologies and the use of realistic reaction drives has a large impact on the nature of the setting.  The common interstellar TL is 10, with 12 being the maximum except for some rare TL13 prototypes and even rarer artifacts from earlier civilizations.

What alien races exist in the Dark Stars ATU?

That depends on your definition of alien.  As I am in the Apes and Angels camp, the majority of non human intelligent life in Dark Stars are those created by man.  This includes not only gene-engineered offshoots of homo-sapiens but also includes uplifted species and artificial life.  As far as true aliens, there is one known but as it does not share the same biosphere as mainstream humanity, they remain rather mysterious.  Traces of ancient intelligent life have been found but there is far more legend than fact surrounding the subject.  At least one truly alien species has, however, been uplifted by man in the past.

What form of FTL travel exists in the Dark Stars ATU?

Rather than break out the technobabble and handwaviums, I'll try to simply explain the effects and general nature of the mechanism.  The basic idea is very similar to Alderson Points, that is to say there exist regions of space where an engine of some sort can basically open/create/spawn a wormhole between two star systems.  Even simpler, consider it as teleporting betwen one star system and another but only from and to certain regions.

These regions I've called Lares regions (mythical guardians spawned by Mercury) as, in the Sol system they would occur between the orbits of Mercury and Venus.  The regions do not orbit the star and are, on average, some 100 light seconds in diameter.  The connections between regions are from nearest star to nearest star with a certain exception - giving at least a nod to causality, Lares pathways can only exist between star systems which have roughly the same time vector in their local frame.

The Lares drives themselves fall into the category known as keyhole drives, they are twice the size and mass of Traveller Jump drives but require no fuel.  Instead they use energy stored in 'capacitors' requiring power and time to charge up.  Travel via Lares drive is effectively instantaneous to those onboard, with respect to the local frames at either end, it seems somewhere around 24 hours +/- 5 hours elapses.  Fleets and convoys may take the extra step of synchronizing their drives so as to arrive at more or less the same time.

The energy required by the Lares drives are only a small portion of the energies required for the transition, the remainder comes from the quantum foam.  There is a release of energy at both departure and arrival time, the release at the departure end is much larger but the energy signature of a Lares drive ship arriving in a system is still quite large.  One side effect of this is that FTL is not stealthy by any means, another is that following a Lares drive ship too closely into a Lares region is a very unhealthy idea.

What does space combat look like in the Dark Stars ATU?

There are at least two different ways of designing the feel of space combat; the first, and most common, is to envision something known and then tweak the physics and rules to fit; the second way, used in Dark Stars, is to model the projected environment and let the chips fall where they may.  So, in some sense, this can't be answered until Dark Stars Ship Design is completed.

However, it is possible to make a few general observations.  First, lets look at what is removed; no gravitics and realistic reaction drives means interplanetary travel will be relatively slow and, while various means may allow a warship to trade off fuel efficiency for raw thrust during combat, delta-V is still a concern.  Also, in the absence of gravitics, laser ranges become much shorter and repulsors do not exist at all.  Shorter laser ranges are somewhat offset by the removal of sandcasters.

Nuclear dampener technology is also removed.  This not only implies nuclear weapons being more effective but also implies that (along with the absence of gravitics) certain types of fusion power plants become less efficient in terms of power produced by reactor mass.  The big one though for most Traveller veterans is: wave bye bye to meson guns and meson screens.

In the absence of both gravitics and nuclear dampener technologies, fusion and plasma guns are not viable.  While combat ranges are most likely much shorter than normal Traveller, flamethrowers have no place in realistic space combat regardless of how hot they are.

Now before you run away screaming about how boring realistic space combat will be, lets look at a few things which never made it into Traveller's OTU, but have made it into the Dark Stars ATU.  Two entirely new (to Traveller at least) weapon systems: Kirklin mines and Casaba howitizers.   Lasers, while getting a nerf to their ranges, get a boost from being drastically upsized in the form of spinal mount free electron lasers.  Heat management has also been ignored in Traveller, no longer though radiators are considered to be armored with IR transparent materials.  There are also changes to armor, generally replacing the more advanced Traveller armors with lighter advanced composites and the use of storm shelters.

Kirklin mines are basically sandcaster cannisters reborn as anti-missile shrapnel mines.  They would be launched by either simple cold gas (mine laying), as a short burn missile, or from a large bore mass driver.

Casaba howitzers are a cross between nuclear shaped charges and directed energy weapons.  A low tech short range bomb pumped x-ray laser replacement.  This weapon would be used as either a stand off missile warhead or fired from a large bore mass driver.  It, in game terms, gives you back the effects of a fusion gun (sort of) but adds radiation damage. 

Dark Stars adds in another consideration that is normally ignored in Traveller, namely moment of inertia as it effects changing faces.  I'll spare you the math, in Dark Stars moment of inertia is worked into a DM penalty to agility and spinal mount accuracy by the subtle means of dividing the length of the warship by 42.  Along with taking mass and surface area into account as well as volume, this implies that very small warships (aka fighters) may be very agile but naked in terms of armor and that very large warships may be very well armored but are sitting ducks and can't hit anything with spinal mount weapons.

Another facet of Dark Stars space combat is, there is no stealth in space!  Warfare at the interface level or in clutter is another story.  Also be aware that nuclear explosions and lasers may, at least temporarily, blind an enemy.

Particle accelerators are refactored a bit, it seems at least some versions of Traveller have ignored that for a neutral particle beam traversing empty, field-free space, the dispersion is proportional to the temperature of the beam.  Charged particle beams suffer from electrostatic bloom and space charge rendering them impractical as space weapons.  In Dark Stars N-PAWs are possibly useful space weapons but their range is even shorter than that of lasers.

Beyond a certain point, adding more armor is ineffective because surface damage can knock any warship out of action regardless of how well armored or big it is since once radiator surface area is reduced below a certain point its a shut off the reactor or boil alive situation.

So what picture is emerging?   Definitely shorter ranges, but not so short (at least at the longest ranges) that evasive maneuver would be ineffective against all weapon systems.  As far as warship size, both ends of the scale are self defeating - fighters and dreadnaughts are both suicidal.  Beyond that?  Well there are still quite a few weapon options and possible mixes.  While lasers look to be awesome at point defense, the possibility of temporary sensor blindness may make relying solely on them a bad idea.  If you're able to get either a large bore mass driver or an N-PAW into short range, it's Katie bar the door time.  I'm projecting that the basic picture will end up being missiles predominate at long range, lasers at medium, and mass drivers/N-PAWs at short range.

Anyhow, that's the overview of the Dark Stars ATU so far.