Re: Interstellar Propulsion idea using an Asteroid and a few comets!

From: AA Institute (abdul.ahad_at_ntlworld.com)
Date: 08/29/04 

Date: 29 Aug 2004 11:46:15 -0700

"Rob Dekker" <rob@verific.com> wrote in message news:<XBhYc.12929$Lg6.874@newssvr27.news.prodigy.com>...
>
> If you move at a snails pace, then you obviously do not need much energy
> for propulsion. So, it would be OK to have a very large space ship be
> moving at a steady pace of maybe 300km/sec (0.001c). That speed is
> achievable with even ordinary (chemical) rockets. The logistics of such
> a ship would be enormous of course, but so is any interstellar space
> adventure.
> Point is, there would be no need for re-fueling along the way, and the
> re-fueling by capturing comets is a very weak part in your idea.

O.K. I agree, with chemical rockets and many other theoretical
propulsion feasibilities one could achieve 0.001c. But travelling at
0.001c would take 4,300 years to reach Alpha Centauri. I can't see how
we could survive on a ship for that long without re-fuelling for power
along the way. Its a catch-22 situtaion. If you embark on a 4,300 year
voyage, then you're talking about a multi-"generation" starship. If
you're on a generation starship, then you need a *substantial*
biosphere/ecosystem of some kind to ensure survival and comfort for
nearly 50 generations. With the BIOSPHERE 1/2 experiments done a
couple of decades ago in the US (Arizona?) I think they both failed
mainly due to lack of adequate *size* (unless anyone knows
differently?).

So you need a large biosphere/ecosystem in operation, let's say of
volume 3km x 3km x 0.2km (ceiling). To house something on that sort of
scale, I don't think a man made framework is possible for a ship to
withstand 4,300 years of bombardments by interstellar debris. To
provide power for 50 generations (assuming zero propellant
requirements for the ship en-route), I would guess you need some kind
of power refill along the voyage. Unless we can somehow scale-up
nuclear fission used in modern power stations to provide electricity
needs of populations in countries like France (80% nuclear) as an
effective guide that shows to the contrary?

Let's say we have a starship of biosphere volume 3km x 3km x 0.2km
(ceiling), population average of 2,000 people in total carried on this
hypothetical voyage to Alpha Cen. How much Uranium (kg) would be
required to power the day to day electricity needs of this comunity of
people, plus all biosphere heating, lighting, etc needs over 4,300
years continuously?

> So either way, it does not make much sense to 'capture' any objects
> during your journey.

I think I've over played this "capture" business with comets and I
need to clarify. You only physically *dock* with comets when you
envisage you are running out of fuel for future maneouvres, or when
you see yourself running out of power for the biosphere/life support.
You remain physically *attached* to such a comet/planetoid only for as
long as you need to draw on its resources (i.e. mine the thing) via a
ship-comet robotic attachment of some kind. You *jettison* the object
as soon as you've completed your resource harvesting to avoid any
excess mass being carried by the ship unnecessarily. You use the
harvested energy to fire your propulsion system to accelerate you back
to your original speed / trajectory toward your destination of Alpha
Centauri.

You repeat the above *only* when you see the ship's computer
signalling "low" on either fuel or power.

>
> Economics are probably your biggest enemy : What's it all gonna cost ?

That's the problem with all spaceflight in the current era. Our
economic system is very restrictive. If they had a complex economic
framework such as ours in the days when the Great Wall of China or the
Pyramids of Giza were built, then those projects would never have
happened.

cheers,
Abdul

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