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

[Kelly St <KellySt@aol.com>]

In a message dated 12/5/97 3:44:11 AM, kuo@bit.csc.lsu.edu wrote:

>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.

Actually we do have working fusion systems.  Some need more efficent systems
like lasers and such.  Others aren't commercially usable to produce
electricity.  But we do have them.

Beyond that plannig on such systems in the next 50 years is highly
conservative even by the standrads of commercial investors.


>>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.

We only figured out mass conversion and fission theories in the last hundred
years.  Expecting we woun't find a few such stagering things in the next
hundred is really better against the odds and history.


>>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.
>
>>Forwards 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.

Don't care about the weight of the sats since we don't need to carry them.
Thats like worrying about the weight of Kennedy launch facilities in
calculating the mass ration of a rocket.


>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.

The cost is at least a good question.  As a rough guess the 160000 to 1 ration
ships fuel would cost 1,600 trillion dollars ($1.6 E 15) at current comercial
rates.  

if you assume 1,500,000,000 watts (I wasn't assuming a 1 g thrust by the way)
and a 40,000,000,000 kilogram fuel sail ship.  Thats about  60 E 18 watts.  At
current power plant costs on earth that would run about E 18 dollars.  So
assuming you only want to launch 1 ship, one time (and assuming no changes in
costs) the staged fussion ship would  cost less.  Thou the microwave platforms
could pay their way selling power comercially, which could complicate the
economics.


>>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.

?  No we have had runing fusion reactions that produced more power then they
took to run, and have other systms that could work efficently at those scales.


>-- 
>    _____     Isaac Kuo


Kelly