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Re: Re: starship-design: Interstellar mission within fifty years

In a message dated 10/15/98 11:44:47 AM, zkulpa@zmit1.ippt.gov.pl wrote:

>> From: KellySt@aol.com
>> In a message dated 10/13/98 11:23:59 AM, zkulpa@zmit1.ippt.gov.pl wrote:
>> >> From: KellySt@aol.com
>> >> 
>> >> In a message dated 10/9/98 9:01:44 AM, zkulpa@zmit1.ippt.gov.pl wrote:
>> >> 
>> >> >I don't think so. Controlling sustained fusion reaction
>> >> >and directing the output to achieve efficient thrust
>> >> >still wait for breaktroughs.
>> >> 
>> >> We don't actually need sustained, 
>> >>
>> >Eh? Do you thing that micro-explosions or similar concept
>> >may lead to a viable starship engine? 
>> Sure, we use micro explosion to power most of our suyrface transports.  No
>> fundemental reason a pulsed fusion drive is out of the question. At a high
>> enough pulse rate all the pulses just form a vibration load, which is
>> handelable.
>> >I doubt it.
>> Why?
>Not because of the word "explosions", but because of the word "micro".
>For a starship, you need rather macro-explosions (and the big 
>"macro" for that). For macro-explosions it will be next to impossible
>to reduce pulsing to mere "vibration load".

Its all a mater of scale.  Scale wise the power to weight ratio of a 1G
starships not that much more then that of a hot sports car able to accell at
nearly 1G. The power of the vibrations should be equally handelable.

>> >I must disagree. Of course funding is necessary,
>> >but all currents concepts how to built it I know about
>> >seem to me to be blind alleys - maybe possible as a laboratory
>> >experiment, but impractical or impossible to scale up
>> >into the terawatt-range needed for a starship.
>> The Bussard designs I used seemed pretty scaleable, the laser 
>> fusion systems looked good.  Natural since we never built 
>> a production copy this is questionable, but for a 50 year timetable 
>> it seems reasonable.  Its not like
>> I'm pitching zero-point energy systems or something.
>OK, but still it is only handwaving at this stage, you must admit.

So were liquid rocket engine designs in the late 1800's.  Obviously nothing on
the shelf is going to do the job.  So we need to figure out what can get from
paper to hardware in the desired time.

>> >> >Not speaking about the waste heat (again - question 
>> >> >of efficiency, but not only).
>> >> 
>> >> Irrelavent.  The waste heat would be dumped into a area of space 
>> >> after The power was converted from sunlight.  Average heat load 
>> >> in the area wouldn't change much.
>> >> 
>> >Just "dumped"? Into what "area"? 
>> >In space you can expel the waste heat by radiation
>> >only, and for terawatt-range power stations that means huge 
>> >high-temperature radiators and efficient enough heat transfer
>> >from the concentrated "reaction chamber" (or lasering medium)
>> >into that huge radiating structure... 
>> >Above some power threshold it may become simply impossible. 
>> Or a hugh number of gigawatt platforms (current SSPS designs) 
>> scatterd over a 1 AU ring.  
>I know, I know, thousands of Chevrolets linked together... 

Hey, a few hundred gigwatts here, a few hundred gigwatts there, after a while
your talking real power.  ;)

Besides we neeed a large baseline emmiter to keep the beem in ffocus over the
desired ranges.

>> >> >Like the space elevator - theoretically possible, and
>> >> >we have even produced an appropriate material (buckytubes).
>> >> >Do you think we will build such an elevator within 50 years?
>> >> 
>> >> I doubt we will ever build one. They cost far more then they are worth.
>> >> 
>> >I do not speak about the cost, but about the technological
>> >(and manufacturing...) ability to actually build it,
>> >provided we have the money.
>> Well we could build one now out of Kevlar and metal if we were 
>> crazy enough to write the checks to cover the STAGERING costs of it.
>No, kevlar + metal is not strong enough. Buckytubes are (barely).

I used to hang with a guy at JSC who was dippy for skyhooks.  Kevlar is strong
enough, you just need a big taper on your teather.  You could do it with
aluminum if you were crazy enough.  (Course the geo sync part would look like
a samall moon...)

>I still do not see technological & manufacturing ability
>to build it now, no matter how big check you can underwrite...
>And the starship is much more hard to build, in my opinion.
>> >> Agree that Apoll made a lot of sence as a cold war "battle", 
>> >> but a historian from 1919 would have found it pretty implausible.
>> >>
>> >I do not think so. There are plenty of examples in history when
>> >political reasons lead to great technological advances.
>> >I think that it is true for MOST of civilization advances...
>> But most look pretty unbeleavable ahead of time.
>Huh? Possibly as concerns the particulars, but the rule
>itself is well-known since some time...


>-- Zenon