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starship-design: debate

In a message dated 12/6/97 12:05:58 PM, kuo@bit.csc.lsu.edu wrote:

>KellySt@aol.com wrote:
>>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.
>We do _not_ have any working fusion power.
>So far, every fusion reactor even built requires more energy to
>start/maintain fusion than it returns.  If you've got something
>to the contrary, I would very much appreciate a reference.

?  We have had several fusion systems where more energy was taped out from the
reaction then took to start it, thou the inefficency of the systems was too
great to get positive payback from the whole system (my favority being the
comercial laser fusion tests in the '80's).  If the systems used better
systems or were scaled up, they would have been able to produce power.  And a
few years ago the DOE annouced one of their systems had reached and exceeded

None of these systems would be comercially usable.  Some could have been
upgraded with current tech to be more usable, but their currently no funding
and little interest.

>Right now, we have working fusion power the same way we have working
>perpetual motion devices.
>>Beyond that plannig on such systems in the next 50 years is highly
>>conservative even by the standrads of commercial investors.
>Commercial investors take amazing risks all the time.  They need to
>do so in order to make their overall profits.  That is the nature
>of investment.  Given the current profitability of the stock market
>compared to bonds, I would have thought that obvious.

Commercial investors never take amazing risks.  Their entire focus is to avoid
amazing risks.

>>>>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
>>>>performance, speed, etc.  But we haven't a clue what might be discovered
>>>>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.
>So what?

So your comment that "Something _might_ be discovered in the next millenia
which will lead to fantastic increases in space propulsion..." is
statistacally far to conservative.  Such things are statistically medium
likely in the next century, virtually certain in a the next 3.

>I know it's against the odds to expect currently foreseeable technology
>to remain the "best" for the next century.
>However, I also know it's against the odds to correctly guess any
>new technology _any_ amount in the future.  Any successful guesses
>in the past are merely lucky guesses, with no predictive value.
>Therefore, anything we would work out a rough design for must come
>from known technology.  Even if we wanted to speculate on unknown
>technology, we'd only be guessing at its performance.
>>>>Fuel/sail avoids a 160,000 to 1 fuel ratio of a pure fusion rocket, and
>>>>cheap and plentifull fuel.  But it requers a massive array of solar
>>>>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.
>But you _do_ have to build them.  That's going to cost--and by my
>estimate cost a hell of a lot more than the fuel you're "saving".
>I make that estimate using mass comparisons, because it's hard to
>say what the actual monetary costs may be in the future.  I make
>the assumption that at any given time, the cost of a ton of fusion
>rocket fuel will be less than the cost of a ton of beam emitter

Mass comparisons are rather irrelavent.  The cost of an ore, vrs a
manufactured systems vary wildly, and are not liniarly related to mass.  So I
can't think of any reason to base cost assumptions on weight.  For example the
cost of a ton of fusion fuel (lithium-6 in this case) could varie wildly
depending on sources found, mining tech, and total consuption.  Similar
factors for the emmiter arrays would have reverse effects (increase demand
would lower the production costs due to economies of scale, vs cost driven by
suply and demand on mining reserves).

>>>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
>>ships fuel would cost 1,600 trillion dollars ($1.6 E 15) at current
>>if you assume 1,500,000,000 watts (I wasn't assuming a 1 g thrust by the
>>and a 40,000,000,000 kilogram fuel sail ship.  Thats about  60 E 18 watts.
>>current power plant costs on earth that would run about E 18 dollars.
>These costs aren't so useful, because they are terrestrial costs.
>It should go without saying that current costs of items on Earth
>probably won't reflect future costs of items in space.  That's why
>I chose the mass based approach.
>>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.
>The only saving grace of the laser sail vs. increased fuel would be
>that the beam emitters may already be built and/or they may be reused.
>For a first interstellar mission (which is what we should be discussing,
>since it's so hard already), it's unlikely they would already be
>built.  There's no way to justify the expense of making them such
>long range other than being meant for an interstellar mission.

Which is another advatage of a dispered phased array system that could be
adapted to longer range without significant modification.  (Even thou the
efficence would decline.)

>The possible reuse of the lasers is particularly notable if it is
>reused in a single mission (e.g. sequencially launching multiple
>modules which provide deceleration fuel).
>However, the possible reuse of lasers for marketable power generation
>is, IMO, dubious.  First, there has to be a market for that amount
>of power.  

Presumably for large scale industrial operations in space, such as non near
earth asteropid work and transport.  But agreed, this is speculative.

>Second, the introduction of that much extra power generation
>into the market will devalue itself.  

Quit likely.

>Third, in this example we
>assume fusion power is available for the deceleration leg.  If that's
>the case, then who's going to bother buying beam power?  

I can't follow this bit.

>All of these
>issues are debatable using speculative numbers, of course.
>>>>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
>>?  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
>Huh?  Give me a hard reference!  This would be very exciting news!

Why?  It hardly made the evening news at the time, and isn't that big of a
milestone.  Its not like they were comercially usable systems, or even
adaptible to such things.  Even if they were, they certainly wern't adaptable
to commercial operation in our power grids at competative prices.  Even the
DOE is grdgingly admiting their tours fusion systems, even if capable of
producing power competativly, could not be used in any power market now

>    _____     Isaac Kuo