31 May 2013

Fuel Revisited

Traveller is famous for using gigantic amounts of hydrogen as fuel for the jump and maneuver engines (well the power plants for those maneuver drives).

It's also famous for not explaining why you need to refine the "wild" fuel you obtain from places like gas giants.

I noticed on my own that hydrogen is a miserable material to keep around.  It seeps through just about any material that can take the pressure and or cold of storing it.  A hydrogen atom is literally small enough to slip between the atoms of the container wall.

Then there's the storage strategies.  You're left with cryogenics or pressurizing it to the point where it liquifies.

Canon Traveller ship designs pretty clearly aren't using pressure in their bunker design, lots of sharp angles and the tankage takes up stray void spaces.  That's asking for a rupture.  Even with better materials, using the stray space method is heavier than proper rounded containers.

Cryo is implied in several sources without them saying it outright.


The jump drive and power plants include the cryogenic systems to keep the fuel cold enough to remain liquid.  This makes hydrogen a super pain in the ass should a leak occur too.  Stuff at this temperature gets brittle and fragile.

The sublimation through the tank walls I'm handwaving away by saying at TL9+ they've come up with a way to "charge" the walls of the tank material to repel the hydrogen atoms so they can't seep out.

Last is refinement.

It's a multi-step process.  First it's mainly refrigeration.  Most wild sources of hydrogen are gaseous.  Second it's separation of impurities, while you can burn the impurities, they might not be aneutronic and those stray neutrons can be hard on the machinery and disrupt the delicately balanced geometry of the fields generated by the jump drive.  Third it's enrichment, protium fusion is lower yield than deuterium + tritium fusion so adding some neutrons to each H as you're storing it effectively improves your fuel density and protium fusion emits a stray neutron (we're trying to stop that).  Included with the refining machinery is a plasma heater that will rip water apart to get its hydrogen.

PS: DT fusion makes neutrons too, but give a higher yield so there's some energy to spare in breeder reactions to suck up those neutrons and using some of the energy making He3 and that will give nice aneutronic 4He with some easily captured protons as exhaust.

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