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Timothy replies to Kelly:

>stage  total weight (tons)     thruster pack and stage structure
>1      1,000,000,000           10,000,000 
>2         40,000,000              400,000  
>3          2,000,000               70,000 ton ship 
>                                 with 5-10,000 tons of 
>                                  drive systems. 
>This assumes a 100 to 1 thrust to weight ration for a fussion drive systems
>(which is questionable), and once you get where your going, coming back is
>out.  But it would give us huge fuel ratios for relativistic flight.
> Possibly a multi stage fusion craft to get to the star and build a fuel
>launcher systems for two way flight?  I'll have to think on this.

I assumed that we could build a variable thrust engine, but for
weight-savings staging may be better.

I think that staging would not solve a more fundamental problem: Pressure
One can see the engine as a force pressing on the back of the ship. We want
a certain acceleration a. The heavier the ship gets, the bigger the force
that is needed to get that acceleration (F=m*a). But assuming the backside
of the ship stays about the same, the pressure (p=F/Area) gets bigger and
bigger. So for a certain weight of the ship the pressure may become to big
for any material to hold. (The backside of the ship is a loose expression,
in fact it would be the support beams that connect the ship and the engine)

>>                      *       LIT "ASIMOV"      *
>>                      *     Starship Design     *
>You might have noticed I hate the name Asimov for the ship.  It gives the
>whole project a grade school feel.  I mean lets be real.  This is a name that
>would never be acceptable to a real starship project.

I never liked it much either, I guess the vote was done by passer-by-ers on
the Web. I can recal that I added the optimistic name 'New Eden' :)
What did you vote Kelly?

>>    * Manned:
>>      * Without crew procreation
>>        * Suicide (explore and die before your time when supplies end)
>>        * One-way (outpost construction and stay till natural death)
>Suicide and one way are the same.  We couldn't biuld a self sustaining
>outpost, and wouldn't fund resupply flights forever unless there was
>something in it for us (or a fantastic improvement in star drives back home).
> NO ONE would fund a one-way flight.

I don't agree with you on that (yet?), I will expect an answer on my letter
of 01-05 10:55.

>>      * Use the interstellar medium
>We have no real idea how to, or for that matter know whats out there to use.

There is just too little, unless we can scoop an area with a 1000 km radius.

>>      * Power from installations at Solar system
>Beamed power or fuel launchers have the advantage of offloading the need to
>carry the heavy fuel (and power systems) with the ship.  That improves the
>ships power to weight ration significantly.  But the systems are difficult to
>do, limit range, and don't seem to help us to slow down.

Also they have a not so good efficiency. (A big part of the beam just flies
along the ship without being used.)

>> 3. Gravity on board
>I think the idea I came up with for a multi segmeny hab ring is the best.  We
>need gravity for the crew, and the rotating hab segments will allow it to
>adapt to changing thrust directions.  Unless the ship can operate under
>continuous thrust for the full flight.  This seem best.

You would always need the rotating rings, because in the time that you spend
at TC you don't have acceleration because of engine-thrust.

>> 4. Mission composition
>Given the size the main ship must be, I don't think we could afford 2.  Which
>is a pity from a safty standpoint.  A robotic pathfinder would be a good idea
>if it would work, but I'm dubious.  
>A suply ship sounds a little risky.  How would you like to be waiting in the
>target system for the next 5 years groceries.

The idea of supply ships is to send them first and wait for them to arrive
savely, unfortunately that would take 20 years from their launch. No a good
way for food.