Re: Best choice of FTL fuel?

All I know about He3 is that significant quantitites of it can be extracted from
the lunar surface, which may be useful for fusion reactors.

scarce, but you can expect a better ratio in gas giants.
Assuming you find He3 there in a concentration of 0,0001% in a H-He
mixture, you'd have to refine 10.000t of gas for 1t of He3.

Not one million tons?

I guess you are right, I mixed up the fraction of 0,0001 and 0,0001%.

That's the trick. I want to hit the middle ground. Neither make FTL travel,
including "wilderness refuelling", too easy, nor too difficult.

Other ideas:
* pure Silicon -- the element as such abounds (say "rock"), but
usually as SiO2 or other compound, so you need to refine it first.
* Iron -- similar as above
* Mercury -- much scarcer than the above, a heavy metal with low
melting point, and toxic to boot so it requires careful handling. I
think this makes for a cool substance to use.

So your FTL just requires energy?

Sort of. The drive is a device that can open "tunnels", but it needs a
lot of energy to do so.

That's one of the things I want to avoid, because then you can just install a
large battery (or capacitor) in your ship, and a fusion reactor (or even a
fission reactor), and you're good to travel anywhere you want for the next
several decades (if not centurires).

I beg to differ. Since all FTL is just magic anyway, you just have to
set a number how much energy you need per ton and lightyear. And a
ship's capabilities to generate energy are always limited. As I said,
the energy yield of fusion isn't that great when compared to
interstellar distances concerning "miles per gallon".
And that way or other, you _always_ need to lug mass around as fuel.
An energy requirement is not "just" energy. You don't get energy out
of nothing.

dynamics of FTL travel in
the Traveller RPG setting

I'm not really familiar with Traveller.

What do you mean when you use the term "torch drive"?

The main propulsion engine of so-called Torchships, i.e. ships with a
powerful drive capable of constantly accelerating at 1 G (or more),
fuelled by large-scale matter to energy conversion. The power source
is sometimes fusion, sometimes matter/antimatter annihilation,
sometimes even more exotic devices.
The term was coined by Heinlein, I think.

But that means unlimited travel endurance for - at least - decades.

Nope. Even if you manage total mass conversion, you get 90e15J/kg and
that's the absolute maximum, and you need to find a way to make use of
that energy as well (M/AM annihilation just gets you a pile of gamma
rays which are "difficult" to make use of). Whatever your power source
and reactor looks like, you're always going to need some specific kind
of fuel.

I don't want to have energy be the "fuel" of FTL travel. I want it to be a
specific substance, with a knowable abundance, so that it is possible to derive
the setting from that premise.

If you absolutely don't want to make it energy-based, I think I'd opt
for mercury.
.

Relevant Pages

  • Re: OT: The Next Hundred Years
    ... The creation of energy has not been a problem. ... I think fusion reactors will eventually be very small. ... but not in our lifetime. ... American Union, I hope. ...
    (rec.music.classical.guitar)
  • Re: OT: New Climate Pact!
    ... > is the start of a campaign to make fusion reactors fashionable again. ... Fission reactors are a nasty technology which is not inherently ... since most things we get energy from on Earth are caused by energy ...
    (uk.comp.sys.mac)
  • Re: Totally new N. Cal Thread
    ... that once an empire always an empire, ... able to impose their standards on the rest of the World, ... that fusion reactors will ever work as a useful source of energy. ...
    (talk.origins)
  • Re: Ten rocket loads could supply all the energy needs of humankind for a year
    ... > This year the energy output of fusion equalled the energy input. ... > Once its scaled up ten times all our energy needs for the next million ... We dont need to go to the moon for Helium 3 at least 20 years, ... The first commercial N Fusion reactors will be deuterium tritium ...
    (sci.energy)
  • Re: Ten rocket loads could supply all the energy needs of humankind for a year
    ... > This year the energy output of fusion equalled the energy input. ... > Once its scaled up ten times all our energy needs for the next million ... We dont need to go to the moon for Helium 3 at least 20 years, ... The first commercial N Fusion reactors will be deuterium tritium ...
    (sci.physics)