Traveller Tuesday: Fusion

In this installment of Traveller Tuesday, I slaughter some sacred cows. 

Traveller Rules-as-written (RAW) indicate that starship fuel is liquid hydrogen (LH2). I find this to be a ridiculous concept, as the requirements for cooling or pressuring tons of hydrogen into liquid form are both wasteful and potentially dangerous.  Here is how it works in my Traveller universe (IMTU):


Fusion 
Power plants IMTU use the Deuterium-Deuterium (D-D) fuel cycle as its base. This produces less power than the Deuterium-Tritium (D-T) cycle -- 3.2-4 MeV versus the D-T's output of 17.5 MeV -- but it has the twin virtues of not requiring expensive/dangerous/time consuming Tritium breeding and needing only a single universal fuel.

Therefore, the Deuterium fusion cycle of a typical Traveller powerplant goes something like this:

Apologies for the crap resolution. If you click through it will be readable.

Or, as a single line,

(For the curious, 43.2 megaelectron volts = 6.92140232 × 10^-12 joules. I'll be honest and admit that I don't really know what these numbers mean, as I pulled them from various articles on the web, but they look large enough that my non-engineer brain has no problem accepting them as suitable output for a starship. If you're an engineer and you spot something wrong with any of my assumptions, please let me know.)


Fuel Refinement
However, since Deuterium is less than 0.02% of all naturally-occurring hydrogen, it needs to be distilled ("refined," in Traveller parlance) before it can be used. Fortunately, Deuterium is stable and non-radioactive -- unlike Tritium, which is (mildly)radioactive and has a half-life of 10-12 years.

So these are the basic procedures of fuel refinement: 

• Take in a liquid or gas with a sizable Hydrogen component (ocean dipping, gas giant skimming, crushing iceball asteroids);
• Crack it into its components, saving useful elements (oxygen) and expelling the waste;
• Separate the Deuterium from regular Hydrogen (a process which can take quite some time);
• Store it in liquid form for later use (see next section).
  

This tells us some interesting things:

1. A fusion reactor that needs to be cold-started cannot use unrefined fuel, because by my definition unrefined fuel is unsorted molecular hydrogen, and power is needed to refine the Hydrogen into Deuterium.
2. Contrary to what RAW says, small craft cannot use unrefined fuel unless they have onboard fuel processors.
3. This also answers the unasked question "Why would anyone buy refined fuel?"  Well, you need it for your small craft and cold-starting reactors.
4. This also has the side-effect of requiring class C starports to carry refined fuel, albeit in limited supplies. I don't see this as a problem, because nearly all C ports have fusion power anyway. If you intend to buy in quantities larger than small-craft fuel tanks, you can expect to pay out the nose for it.

Fuel Storage
Even though Deuterium is stable and non-radioactive, it's still hydrogen and therefore explosive. Just the kind of thing you want sitting around a busy starport in large tanks, or surrounding the crew and ammunition in a starship, right?

Therefore IMTU, fuel which is in the tank (as opposed to being in the reactor) is converted to a more stable form.  Civilian ships* convert it to ammonia for storage - specifically, triply deuterated ammonia, which is three atoms of Deuterium bonded to one atom of Nitrogen.**

Ammonia is poisonous, yes, but it has the following benefits over liquid Hydrogen:

1. It's not explosive.
2. It doesn't need compression or refrigeration to be a liquid.
3. It's not explosive.
4. If there's a leak, you can smell it (much like why natural gas has additives).
5. IT'S NOT EXPLOSIVE!

The nitrogen used to convert the D to ND3 is part of the life-support system, as it is added to the oxygen reserves to create the nitrogen-oxygen mix that humans enjoy breathing (with the pleasant side effect of reducing atmospheric flammability). A single tank of Nitrogen will serve a starship for a long while, as it is being constantly recycled from the air to the tanks via the life support system (there's lots of Nitrogen in urine).


*Military ships convert it to a metal hydride form which, while bulkier, has the twin benefits of not exploding and serving as secondary armor.

** I am aware that ammonia is bulkier than liquid hydrogen and therefore NH3 contains less H per unit of volume, but since we're dealing with handwavey units of "H per dton" and it's universally applied across the board, I can claim that the required tonnage is for NH3 instead of LH. As long as everything is consistent, I don't think there's a problem here.


In conclusion

• If the ship has a life-support system, it can convert deuterium to ammonia and back.
• If it has a fuel processor, it can refine hydrogen to deuterium.
• Your pee helps make the ship go.