On Tue, 29 Jun 2004 20:28:51 -0700, Hephaestus wrote: [...]
Basically, once you decide not to go 100% reusable, you have the ability
to decide certain components (tanks, structure, etc) just aren't cost
effective to reuse. Right?

I worked out once shortly after Columbia broke up that for the same cost
as a single shuttle mission, you could launch the same amount of cargo,
personnel and habitat space on multiple Russian launches for about half
the cost. I was figuring on a Soyuz capsule for the crew, and two
heavylifter launches for the cargo; one for the habitat module, and one
for the cargo. I believe I opted for a Proton, although it could have been
an Energia. Once safely aloft, the Soyuz would dock with the habitat
module, which would then rendezvous with the cargo, whatever it was. The
only part of the whole assembly that would return to Earth would be the
crew. Everything else would be discarded.

(Unfortunately, I can't find any of my reasoning --- it's lost somewhere
on the web and Google's being uncooperative.)

Of course, this was a very simplistic analysis. The major cost I didn't
include was the design and construction cost of the habitat module; you'd
need one of these every time you wanted a mission aloft. However, given
that it doesn't have to be man-rated on launch, only on orbit, and that
once the decision has been made to make it disposable it's possible to
simplify construction considerably --- fuel cells rather than solar
panels, thrusters rather than gyros, etc --- I would expect the long-term
cost per unit to be quite small.

I opted not to reuse *anything* mostly because it made the calculations
simpler. (All the off-the-shelf components I was using were disposable.)
It might be worthwhile to reuse some components. The habitat module is a
prime example; if its consumables allow, leave it in orbit and use it
again. Think of it as being a short-lifetime space station. (Reusability
does not necessarily mean that you have to bring it back to Earth.) Also,
you may not want to deorbit them once you've finished with them --- even
as dead mass in orbit, they're valuable. If your orbit allows, add them to
a station-keeping platform; an orbital scrapyard. As and when technology
allows, it may be cost-effective to reuse them, or at least mine them for
components.

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