[extropy-chat] FWD [forteana] Re: Are dwarfs better forlongduration spaceflight?]

Adrian Tymes wingcat at pacbell.net
Tue Sep 6 06:46:08 UTC 2005


--- spike <spike66 at comcast.net> wrote:
> > Actually, considering how small a fraction makes up the crew and
> crew
> > support - the "payload" - of any manned space vehicle to
> date...yes, we
> > are talking about shaving close to the margin...
> 
> Ja, ok I see now where is the disconnect.  Assume the
> surface-landing manufacturing machinery is launched
> separately, sent on ahead.  It can go with slow, highly
> efficient ion drives, all the tricky stuff, since it
> has no consumables.  The hab module is in a hurry, so
> it will likely use chemical rockets on a Hohmann 
> transfer orbit.  

Doesn't help enough.  Even if we're just talking a one-person
spacecraft to Mars and back, the constant thrust of a nuclear rocket
would beat out the higher ISP but lower total thrust of chemical
rockets.

> The design exercise is now just the human 
> hab module.  In that scenario, I imagine the
> vehicle as a spherical shell about 4 times her height.
> The propulsion system scales with the mass of that shell,
> which scales as the cube of the diameter.

The scaling factor of different propulsion systems trumps the
difference in crew dimensions.  For example: calculate how much rocket
you would need to make the trip in a few months (one way) on hydrazine.
Then calculate how much you would need for nuclear propulsion.

But you're still missing the non-physics objection: the economics and
practicality of finding and training that one perfect (by your
guidelines) person, not to mention the cost of specializing habitat
manufacture (which would ordinarily be partially borne by other
missions hoping to send their own people up, but could not because your
habitat rules out the people they wish to send), would seem to impose
costs that at first would grossly outweigh the savings you'd gain by
slightly reducing the mass.  Physics is not the only determiner of
economics, but economics is quite often the determiner of whether you
can or can not pull off a project of this nature.

Remember: *practical* optimism!  ;)



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