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starship-design: Re: Re: debate

In a message dated 12/9/97 11:55:52 AM, kuo@bit.csc.lsu.edu wrote:

>>>>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.
>Untrue.  They regularly invest large sums of money on speculations
>which may fail, and when it's other people's money it can make big
>news when the bet fails.

All investments are risks.  "amazing risks" suggests an unusually high risk

>The larger the sums of money, the more risk investors take.  On one
>end of the spectrum are personal savings, which require a low risk
>strategy in order to save up retirement funds safely.  On the other
>end of the spectrum is Bill Gates, who has so much money to spare
>that he can afford to risk most of his eggs in one basket--his own
>company--because it is the most profitable place to put it.  There's
>maybe a 5% chance that a some "disaster" will cripple Microsoft
>stock--that's too much of a risk for anyone to put their entire
>retirement savings into Microsoft stock alone, but Bill Gates can
>afford to put the vast majority of his money in Microsoft stock
>because even in the worst case what remains is plenty.

No, thats not what risks mean.  Gates invests in MS stock because it gives him
more control in his company and because (as you stated above ["There's maybe a
5% chance that a some "disaster" will cripple Microsoft"]) its a very low risk

>>>>>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
>>>>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.
>No, I don't think so.
>Sure, something will lead to fantastic increases in space propulsion
>compared to TODAY's technology.  But look carefully at what I say.
>I say, "Something _might_ be discovered ... which will lead to
>fantastic increases ... beyond the theoretical anti-matter rocket."
>Beyond the theoretical anti-matter rocket.
>I have great confidence that for interstellar travel something on
>the level of a theoretical anti-matter rocket or less will remain
>the best we can hope for in the next millenia.  The physics of
>relativity and conservation of energy strongly suggest this.

The physics of relativity and conservation of energy have only been developted
in the last century.  They are not the end of physics research, nore are they
likely to be the ultimate form of power or rocket physics.  Research into
newer physics, capable of far greater power, performance, etc (zero point
energy, inertia/mass damping, etc) has progressed to the degree that NASA is
funding some conferences and studies on them.  So I would estimate that the
odds that current physics (like the physics of relativity and conservation of
energy, or mass conversion rockets) will not be greatly surpassed in the next
century, are about nil (assuming no colapse of civilization).

>>>>>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.
>Yes, they vary wildly--but in all cases the cost of the manufactured
>system is more than the cost of the raw materials used to manufacture
>it.  This should be obvious.

But they are not made out of similar materials.  For example an IC chip made
out of silicon may or may not be worth its weight in gold.  Or the cost of
gold could increase or decrease by orders of magnitude.

>The costs of various raw materials may differ, but fusion rocket
>fuel (Deuterium and possibly Hydrogen; D-D fusion is trivial if
>we have Li6-H fusion) will very likely always costs less than
>the metals/composites used to manufacture beam satellites.

Deuterium, He3 and other exotic issotopes is extreamly rare and difficult to
aguire, so its cost per pound could be hundreds to thousands of times as much
as Li-6, and likely to cost far more pound for pound they an equal weight of
solar power sat, much less they the equivelant weight of silicon, iron, or
aluminum (the major materials for solar power sats).

>>>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.)
>Huh?  Advantage over what?  A dispersed phased array system can't
>be adapted to longer range without significant modification.  What
>_can_ be done is to increase it's efficiency by bunching it up
>together as tightly as possible, ideally shoulder-to-shoulder.
>The only thing you gain by dispersing them over a wide area is...
>you don't gain anything, actually.  At every range, the beam
>produced by the tightly bunched up array is superior to the
>beam produced by the widely dispersed array.

You gain increased range due to the larger virtual lens from the array.  Being
able to focus the beam acuratly over interstellar distences was identified as
a major problem by the group a year or two back.

And yes the phased array planforms are likely to require fair little
modification to do this.

>>>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.
>The only serious use for them I can imagine is for laser powered
>rocket transport.  Assuming nuclear reactors remain expensive and/or
>fission materials remain restricted, laser powered rockets offer
>great potential savings in rocket costs.
>For any sort of heavy industrial work where it's worth putting a
>high power refinery on site, it's also worth putting its power
>source on site.  Beamed power really only offers a potential
>advantage in cases where the power is only needed a small fraction
>of the time (which is the case for rockets).

Since the refineries and propulsion platforms would need to relocate around
asteroidal space, being able to buy a couple months powe without shipping a
power plant to the site could make a lot of economic sence.  With the power
levels this system is capable of it could directly melt ore bearing asteroids
by transmitted power.  With a little workl it could be used to "blow" a metal
asteroid into a hollow cylinder of sphere like a glass blower.

 !!!!!  Or it could be used as an asteroid clearence system to burn everything
out of earth crossing orbits!  That might make the system more saleable?!
Humm..  probably an overly complex and expensive way to do that thou.

>>>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.
>The affordability of the powerful deceleration leg fusion rocket
>(that we can afford it at all) suggests we have similar fusion
>power generation capability which is relatively affordable.
>Given the plentiful inexpensive energy everywhere, who's going
>to need beam power?

Saying you have fision power, does not mean its the cheapest form of power,
nor the cheapest way to get power to a remote area.  We have nuclear powe
plants, but still fire foundrys with coal.

>    _____     Isaac Kuo