Roger Books:
> I think I may have to argue this one.  If you can't put stuff in the
> hold
> worth many times the cost of the shipping interstellar commerce won't
> occur.  

Well, this is why I said you must be very careful with the exact
balance. 

And when I talked about reasonable stuff, I meant military equipment
(reasonable in the context). This would not preclude making a buck out
of
shipping something more rare and valuable, e.g. "spice".

Go read Greg Costikyan's article "The 11 Billion Dollar Bottle of Wine"
at http://www.crossover.com/~costik/inttrade.html

It has a general piece, plus calculations for Traveller.
Basically, he came to the conclusion that it's not profitable except in
some rare cases -- *even* assuming the liberties Traveller takes with
the
laws of physics...

There's also different kinds of shipping. E.g. it would be horribly
expensive to fly to Pluto *right* *now*, with current tech. But if you
could magically set up a base there, it could be reasonably inexpensive
to
launch chunks of iron ore back here (yeah, I know ice, not iron, would
be
the most likely export for Pluto...).

You want your troops and tanks there *intact*, and *asap*. Typically,
they
also want to come *back* the same way. The stream of ore they're
supposed
to be chucking back can take a bit of beating and doesn't mind if it's
in
transit for 500 years or never goes home again.

And yes, this *does* mean that shipping plain leg infantry (at least
until
good cryogenics are available) is just about as dumb a military move as
you can make. Humans take space, consume food air and water, are
sensitive
to temperature levels, produce waste etc.

> Without interstellar commerce there is no real reason to be
> "out there".	Why go force a rebel colony back in the fold when you
> are never going to turn a profit off of it anyway?  Let your
> enemies^H^H^H^H
> competitors drain themselves shipping things through space.

Yes, this *is* a possible result. In fact, it is even likely at the
first
stages of interstellar travel. The first colonies are very likely not to
be profitable for generations -- which ofcourse brings the question
who'd
fund such a thing, which in turn brings the shadow of doubt over all
this
interstellar stuff...

> To rephrase, if I can make money shipping food with a bulk hauler I
> can use that same bulk hauler to move medium or low tech tanks 
> reasonably.  Even a "Low" tech tank is not a cheap piece of 
> machinery.

Err... stuff like food and basic raw materials are on the bottom rung
when
it comes to profit per pound. It *is* highly likely that interstellar
shipping of them "old-style" (i.e. with a manned cargo ship) is not a
viable economic venture in any semi-realistic background. You don't see
much water shipped around the globe today, do you? Unless it's bottled
with an "Evian" sticker ofcourse...

The fact is, as we currently understand the world around us, the odds
are
very much stacked against an interstellar culture. The odds are very
much
against going en masse to *any* other planet, even the closest one.

One could just do some hand-waving, say it's a space opera and assume
the
universe is just our old earth with different background paintings and
props. Nothing wrong with that, but if one goes down that road, one
might
just as well throw out the remaining bits of realism with a little more
PSB. Why bother with ships? Just assume everyone teleports to combat.
Why
bother with tanks and guns? Just assume all conflicts are peacefully
settled in UN assembly meetings...

Also, PSB is an insidous thing. It typically has holes, which you cover
with more PSB, which has holes of its own, which you cover with...

OTOH, if one wants to retain the suspension of disbelief, one must set
the limits. And those limits, being "laws of nature", affect
*everything*,
including civilian traffic and trade, which in turn affects the reasons
why anyone would want to fight over West Bumfuck and with how much
resources. It's a vicious circle...

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