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Re: Engineering Newsletter

ReplyFrom: Timothy
Subject  : LIT

>BTW,  has anyone kept all copies of the Mini-LIT newsletter to put in the 
>archives?  I must admit I have not.

I did, if some one needs it, ask...

ReplyTo  : Kelly
ReplyFrom: Timothy
Subject  : Drawings

About the drawing: where did you plan the shielding. And does it ride along
with the hab ring, thus at 1 g?
I had in mind that we made a shielding tube in which the hab-sections
rotated. So then the shielding would not move and would not create an extra
outward stress-factor. 

>>> What program did you use. 
>RayDream designer 3.  They were selling it for $100 bucks in MacWarehouse and
>such a while back.  So I picked it up.  Won't run on the old Macintosh Plus I
>have at home, but it runs like a bat out of hell on the new power Mac I have
>at the office.  I figured it would encourage me to get a new computer faster.

If any one else likes doing raytraces, you can get PovRay or Radiance for
FREE on the internet. I use PovRay and can make the same kinds of drawings.
These are well know raytracers and work great. These programs are available
for different platforms.

(Tip: jpeg images would be about 4 times smaller, so would mean a less bytes
with almost the same image quality)

>Far larger than that.  A multi generation ship would be technically far
>harder then a fast relatavistic ship.  To have half a chance it would need to
>be compleatly self contained and self sufficent.  With enough fuel and
>resources for decades to centuries.  Say a couple times the size of Manhattan
>and with a population of hundreds of thousands of people.  All that assuming
>a big jump in technology to support it all with a crew that small.

Indeed the ship itself would probably bigger than a rel. ship but, I don't
think that energy will be a problem. The amounts of energy needed for a rel.
ship are far more. It's quite easy to calculate the amount of energy that is
needed for a self sustaining system. On Earth the energy income is 1400
Watts per square metre. With that energy all plants and animals seems to do
well. Now the question is how much space per person is needed. Say 10000
square metres? That makes 4.4E14 Watts per person per year. The rel. ship
engine would use 1000 times more per second. So now the only problem is to
build that large ship. Material from astroids would probably be the main
source. At the outer part of our solar system there seem to be billions of
them in all the sizes you want.
Making a self sufficient system should not be that hard with enough energy

ReplyFrom: Timothy
ReplyTo  : Kevin and Kelly

>>> _BUT_
>>> the conversion would take place on the antenna itself.  
>>> diodes wired directly onto the metal mesh would do the
>>>  power converting and the mesh  (of special radiator fins 
>>> if need be) could radiate the heat.  we have thousands and 
>>> thousands of square meters of antenna, it would serve as 
>>> an exceptional radiator.  ----
>I'll buy this part.  With the hundreds to thousands of square kilometers of
>mesh you've been taling about you have a lot of radiator space.  Asuming you
>can radiate the energy away fast enough to keep everything down to operating
>temperature.  If you want supper conductors this could be dicy.  They like
>cold temps and radiators like it very hot.

I don't buy that part: Take 1 square kilometre or 1E6 square metres, that
means 1E18/1E6=1E12 Watt per square metre. Take 10% of that and you get 1E11
Watts of lost energy per square metre. That sure would melt anything away.
Even with thousands of square kilometres it is still too much.

>Kevin, the heat your talking about is enough to provide for all the
>electricity for a few thousand cities the size of Chicago!  Thats the kind of
>power that keeps all those cities outside air temp a few degrees above
>country temps.  You can't just brush that off by saying the engine will be a
>few klicks long and were can pump a lot of heat into the reaction mass.
> (Frankly I doubt the reaction mass can absorb that kind of heat load.)  This
>is a lot of power, and we need to know what were going to do with it or the
>ship will cook itself alive.

I agree. Also super conducting wires don't like very heavy currents.

Subject  : Photon energy
ReplyTo  : Kelly
ReplyFrom: Timothy

>>no, I am talking about the momentum of the photons as opposed to the 
>>momentum of the ions the "Asimov" will eject as exhaust.  Those will be 
>>Hydrogen ions or maybe Xenon moving at .9996 or (.99996, depending on how 
>>much energy you can invest) C  at these speeds, a small mass flow is 
>>sufficient to slow us down (or speed us up depending on which phase of 
>>the mission we are in) at a constant 1 G.
>>> This was clear to me, but rethinking this made me 
>>> realize that your method can't work. Because adding 
>>> momentum to the Asimov will only make it move
>>> faster. Transforming it to reverse momentum would 
>>> surely break one of the basic physic laws.
>No Tim.  The momentum of the microwave is simply added load on the antena
>support structure (which is an extreamly unlikely structure) assuming it can
>take the load the power (electric) them feeds the engines which use it to
>produce forward or backward thrust.  No violation of conservation of
>momentum.  As long as the engine is powerful enough (and antenna strong
>enough) to overcome the thrust load of the photon sail effect of the big
>antenna.  Every thing is fine.

No, that's not what I meant. I think that the energy that is gained by
receiving the photons is not enough to overcome the velocity gain that you
get by receiving these photons. So a powerful engine doesn't work because
there isn't enough fuel.

Subject: Solar array
ReplyTo  : Kelly
ReplyFrom: Timothy

>Are you talking about a 5 kilometer disk a million kilometers from the suns
>surface?  Does this not strike you as a servicing problem?

In fact I was talking about a 50 kilometre disc...

>Solar Power Density out here by earth is 1.35 KW/m^2 not the 5E8 Watt/m^2,
>but the equipment will be a lot more likely to keep working.

I agree completely, but having it so near Earth means a much bigger array.
5E8/1.35E3=3.7E5 times bigger to be exact. That is about 1.5 times the
surface of the Earth!!! That seems to be an even bigger problem :)