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Fwd: starship-design: AsterAnts



Curtis Manges writes:
 > > ... Oh wait, their is no launch cost for water.  Its just caried along on 
 > > shuttle flights to carry crew or other suplies.  The extra weight isn't 
 > > significant, and causes no real increse in shuttle costs.
 > 
 > Excuse me?? I thought _everything_ had a launch cost. And the weight
 > _is_ significant, about 60 lb/cubic foot.

I have this vague memory that a lot of the water they use on shuttle
flights is produced as by the fuel cells they use to generate power.  So
in a sense they may be getting their water for free; the money was spent
on launching the fuel.

Note that the per-pound launch costs quoted for payload are typically
calculated by dividing the cost of flying an entire shuttle mission by
the weight of the payload.  Water carried for crew use _isn't_ payload
and therefore won't have much effect on the payload launch cost.

The cost per pound to put the entire shuttle in orbit is quite a bit
less than the payload launch cost; the payload is only a fraction of the
entire shuttle weight.