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

[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:
>> 
>> >> From: KellySt@aol.com
>> >> 
>> >> breaktrough to me implies a fundamental jump in science or technology.  
>> >> I would see where fusion or huge laser system would require eiather. 
>> >> The fusion and microwave sail system I last sujested seems to 
>> >> require none.
>> >
>> >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?


>> and certainly thats not a major 
>> breakthrough eiather way.  Now the fact no one is doing any real 
>> applied work in fusion is a major problem for our timeline, 
>> but it seems fairly likly a fusino drive
>> would get funding in the next few decades.
>> 
>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.


>> >Concerning lasers/masers, we are speaking of GIANT lasers -
>> >that is, teravats of power - with current solar cells it means
>> >tens or hundreds of kilometer arrays, which makes it
>> >highly impractical, if at all possible to build
>> >and keep in operation for tens of years.
>> 
>> Thus my assumption of the nessisity of automated productino of thousands of
>> SSPS platforms.  A ring of them around the sun at 1 AU should do it.
>> 
>I forgot the English equivalent of the Polisk proverb: 
>"Zamienil stryjek siekierke na kijek"...
>It means roughly that you exchange one big problem 
>for another, possibly even bigger...

Could be true.


>> >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.  



>> >The question of scale is important - for interstellar
>> >propulsion, scales of energy, size, mass, etc. are orders 
>> >of magnitude larger than any tested by humanity till now,
>> >which really calls for breaktroughs to make it work.
>> 
>> Manufacturing breakthroughs yes, but not science and tech breakthroughs.
>> 
>First, manufacturing ability means having an appropriate technology too.
>Second, there are enginering, material strength, heat transfer, etc.
>limits and thresholds that do not scale up indefinitely.
>Because of that the aircraft-carrier engine is neither a magnified
>Chevrolet engine nor some thousands of Chevrolet engines
>linked together, but a completely new design.

In this case I'm not scaling up the systems being manufactured, just the
number of them being made.



>Our technology has NO experience with size and power scales
>needed for a starship systems. At these scales, quite new problems
>will emerge, and thus corresponding completely different designs
>will be needed - to be invented, built, and tested...

I'm avoiuding that be using vast numbers of more conventional scaled systems
in the emmiter ring.

Now the big fusion motors on the starship are an issue, but they should scale
up pretty well (its down thats a problem).



>> >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.



>> >And a viable starship is even harder, in my opinion...
>> > 
>Let repeat the above once more...
>
>
>> >> A big problem is the two are competitors.  
>> >> So if fusion is developed, space solar would likely be abandoned.
>> >> 
>> >Not necessarily. They may find different application niches.
>> 
>> That seems unlikely. Space solar has enough disadvatages that I don't 
>> think it could compete in a economy with fusion systems.
>>
>Not necessarily. E.g, on Mercury there is plenty
>of solar power, but all hydrogen (or other fusion fuel)
>is most likely to be completely absent.
>It is the other way around near Jupiter...

Fuel is light weight, and solar systems are a relyability and cost headach.
If you got fusino, you wouldn't bother with solar power in space unless you
just want bulk heat for melting stuff.


>> >No, it had a pretty good sense - that is, political (mostly):
>> >to show those Ruskies that we are better anyway (after the Sputnik).
>> >And a technology advance sense too (mostly subordinated to political).
>> >Unfortunately, by lack of determination and, let us say, simply guts,
>> >most of the technological & political thrust produced by Apollo
>> >was promptly wasted.
>> 
>> 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.


>> Tech development was no a goal for Apollo. As a mater of fact it was 
>> avioded as much as possible, hence the crude space capsule expendable 
>> booster concept.
>> 
>I wrote also about this in another letter.
>Of course, since one of the biggest factors was time,
>if something could have been done with existing technology,
>it was - it is a safe and fast strategy (it is also
>used in Zubrin's Mars Direct project - and justifiably).
>Despite that, Apollo did lead to technology developments too.

Reply in other letter.


>> >As, fortunately, I do not think that we will have United States of Earth
>> >within 50 years or so, the political sense for going interstellar
>> >may surface again. Especially with space/Mars/asteroids/etc. human 
>> >colonies in place - either one/some of them will want to show its
>> >independence and advanced technological power to those dirty Earthmen, 
>> >or Earth power(s) will want to be the first at this next technology 
>> >power step.
>> >Though I am afraid it will take more than fifty years.
>> 
>> Agreed.
>> 
>You see, so even we CAN outperform your "historian from 1919".
>I also think that that historian was smart enough too,
>despite your doubts...

  ;)


>-- Zenon

Kelly