Re: Re: starship-design: Re: Perihelion Maneuver

[kuo@bit.csc.lsu.edu (Isaac Kuo)]

KellySt@aol.com wrote:

>Agreed.  Best we can do is pick likely or unlikely advances, and keep to
>systems that seem to have a good mix of simplicity and performance.

I would argue we pick only _very_ likely advances.  Either that or
admit that there's no particular reason to think the design will
_ever_ work.

For instance, any design which requires fusion power other than from
H-bombs is speculation.

>For example:

>If we wait for physics to come up with major changes (zero-point energy,
>inertia damping, gravity control, etc..) we could get fantasic increases in
>performance, speed, etc.  But we haven't a clue what might be discovered and
>perfected in the next 50 years.

I seriously doubt any of these will be a factor, ever.  I'm in the
majority camp which figures that the density of zero point energy
is uselessly small.

Something _might_ be discovered in the next millenia which will lead
to fantastic increases in space propulsion beyond the theoretical
anti-matter rocket.  If so, I'll bet it won't look anything like
anything we've imagined.

>Anti-matter ships have great performance, and use known physics, but carrying
>hundreds of tons of the stuff for decades is a major problem (and danger to
>nearby solar systems!), the engine designs have serious problems compared to
>fusion, and the manufacturing expence for the fuel would seem to dwarf the
>other ideas.

Don't forget that anything using fusion power other than H-bombs is
speculation.

An antimatter rocket, unlike a (non-H-bomb based) fusion rocket, could
conceivably by designed and flown using current technology.  It would
be fantastically expensive, and perform worse than a bottlerocket,
but it could conceivably be done.

>But if we could cut the cost down, or create antimatter on
>demand with a light low power systems (might be possible with some theorized
>physics tricks) it would be great.

>Bussards laser sail idea is light and efficent, but the drop sail idea
>requires you to keep hundreds (or thousands?) of square miles of unanchored
>foil precisely shaped into an optically precise form focused on a high speed
>moving and manuvering target, that it can't see.

It's not light or efficient.  But it could theoretically work.

>Fuel/sail avoids a 160,000 to 1 fuel ratio of a pure fusion rocket, and uses
>cheap and plentifull fuel.  But it requers a massive array of solar powered
>microwave sats in our solar system.

You were looking to avoid a mere 160,000-1 fuel ratio?  In favor
of a 400-1 fuel ratio?  Just how lightweight did you think the
microwave satellites were going to be?  Show me numbers.  Power-weight
ratios.  Desired output thrust.  I'll bet that given any reasonable
numbers, you'll find that the mass of the microwave emitter satellites
will end up weighing more than 400 times the sailship.

For every kilogram of sailship, you need 1,500,000,000 watts to
push 1 gee.  Assuming your emitter satellites were 500 times the
mass of the sailship, that means they have a power/weight ratio
of at least 3,000,000 watts/kg (this includes the collectors,
emitters, and lenses)!

If you can't even do that, then you're massive array of satellites
is going to weigh more than the huge amount of fuel you're trying
to avoid using.  And I'll bet you that fuel costs less per kg
than microwave beam satellite.

>All in all we are down to designs that seems extreamly expensive, but
>possible.  Or ones the requre unknown physics or technology.

Positive feedback fusion technology, other than H-bombs, is unknown
technology.
-- 
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
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