Re: Best choice of FTL fuel?

nuny@xxxxxxx wrote:
On Jul 24, 12:24 pm, Peter Knutsen <pe...@xxxxxxxxxxxxxxxx> wrote:
Nevermind *how* FTL works.

Nevermind *how* your car works, just think up an interesting fuel
for it.

Yes.

The point is, it needs some fuel, because fuel-using
FTL makes for *better* worldbuilding than non-fuel-using FTL. It works, and
that's it, we don't discuss how or why, but we do know that you have to feed the
hungry engine with some regularity.

For values of "better" ~= "makes material resource allocation/
conflict themes available to storyline" maybe.

Yes, although it isn't just a storyline issue but also a worldbuilding issue. You decide on the premises, then you derive the world from those premises.

The question then becomes, what substance should be chosen by the world builder
as the required fuel?

Horse, then cart. Your thinking is why we don't dare look too
closely at the details of things that sound cool on the surface like
certain sub-genres of steampunk, Baxter's _Anti-Ice_ notwithstanding.

The fuel should be one that stores enough energy to make the FTL

I'm not interested in the physics of the the FTL drive works, and therefore not interested in energy issues either.

drive work*, be cheap enough to be commercially viable, be safe enough
to store on ships with humans aboard, and so on. BTW, why should there
be only _one_ fuel? Space piracy would be a lot riskier (i.e. more
interesting story-wise) proposition if the next ship you boarded
carried Diesel but you burned gasoline (so to analogize).

Because it ends up looking as if the author is giving himself permission to stick his hand up his own ass and pull out a new type of FTP fuel, whenever he has painted himself into a corner.

The famous Traveller RPG setting uses ordinary hydrogen,

If that's your preference then use it; don't waste everyone's time
justifying it.

First of all, I'm not asking for justification. I'm asking for suggestions, and I'm asking for suggestions based on astronomical knowledge, meaning knowledge about how abundant various substances are in different places.

Secondly, I believe I have explained why I'm rejecting hydrogen as a possiblity: It is *too* common.

[...]
and confine ourselves to known substances, as well as materials that
scientists assume to exist somewhere out there.

You mean as an energy-storage medium? You _are_ aware that empty
vacuum theoretically holds more energy per volume than any possible
form of matter? Yes, the trick is getting it out, but still.

Vacuum as FTL fuel is even worse than hydrogen as FTL fuel.

(snip H/He dither)
What other FTL fuel choices are there, if one recognizes the fact that
compications and logistical problems make for better worldbuilding than
"push-the-button-and-it-goes" problem-free wonder technology (much as I like
Iain M. Banks' stuff)?

That's not only not SF, it's not any kind of fiction; just fantasy!

Even an FTL drive that used vacuum energy would need maintenance.

Most maintenanc can be performed aboard ship, possibly even in flight.

My interest is in getting things just about right, such that long-distance expeditions become possible without becoming trivial. That requires that it be possible to refuel in unsettled solar systems, and that you don't have to return to dock every 4 or 6 months for maintenance.

Apart from abundance, ease of transport may also be important. How difficult is
it to move helium? Liquid hydrogen isn't too easy, as far as I know, but we have
some idea of how to do it, and we're gonna become much better at it in the next
couple of centuries.

Well, vacuum is available literally everywhere free of cost, takes
up no storage space, and carries no inertial mass penalty.

I'm looking for the sweet spot. A substance that is neither too abundant nor too rare.

Ideally, starships should spend quite an amount of their capacity (mass) on FTL
fuel storage, if they want much range (or speed); not entirely unlike the
Traveller RPG setting.

Look, if you like the Traveller universe _that_ much, just write in
it. Apparently they do the shared-universe license thing, or at least
have according to Wikipedia:

I don't like that Traveller RPG setting that much. That's why I'm looking for alternatives to hydrogen as the FTL fuel.

http://en.wikipedia.org/wiki/Traveller_(role-playing_game)

see "Traveller in other media".

As for how much of a ship should be tankage, a vacuum-fueled ship
wouldn't need any but the size of the engine that extracted energy and
applied it would be proportional to the size and desired speed of the
ship, I'm thinking.

I'm not looking for the solution that requires the last amount of tankage. That would be what is most convenient from the characters' point of view, and from the human species' point of view.

I'm looking for the optimal solution from a world builder's point of view. I don't want to make things too easy, for the people living in the setting.

*Considering that just to get to c (much less past it) you need
_infinite_ energy, what possible fuel will do?

Irrelevant to my question.

--
Peter Knutsen
sagatafl.org
.

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