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.