Jan C. Vorbr?ggen wrote:

But the Russians _do_ use (basically) the same ship to move people and
cargo, and even sometimes both in the same mission.

Putting in a dogmatic division between personnel and cargo transport is
stupid.

On the surface, I'd agree ... but then you've got
to consider that there are significant differences
between a cargo-only vessel, something which carries
passengers PLUS cargo and something which carries
only passengers (+ trivial cargo).

Cargo-only allows you to cut out a LOT of the systems.
With no precious, perishable, humans to support the
entire environmental package can be scrapped, plus you
can go from triple/quadruple-redundancy to mere double.
If your cargo vessel is expendable, then you can drop
all the re-entry crap too - vastly simplifying the
design, reducing weight and eliminating recovery and
reconditioning expenses. Big cargo pods might be left
in orbit - to be later incorporated into a space station
or simply as a source of spare materials - metal, wire,
plastic, insulation etc..

Because of all this, an expendable cargo-only system
would be comparatively cheap - especially after we
standardize and mass-produce the major components - and
have fewer systems that we mere humans could screw up.

Passenger-only vessles can be physically small and of
robust construction. Size matters when it comes to
putting things into orbit and also matters when it
comes to maneuvering IN orbit. A passenger-only
vessle can also be OPTIMIZED for that role, which
means fewer compromises that might come back to
haunt us (or wind up scattered over Texas).

The WORST plan is what we have now ... a compromise
vehicle. Big and unweildly, trying to support people
AND cargo-carrying needs. The only nice thing about
the shuttles is the convenience of having people in
the same ship as the robotic arm and immediately
availible for EVA. However, the arm could as easily
be controlled from a nearby ship, and as far as EVA
goes, the passenger shuttle could literally be
docked to the cargo pod.

Cargo ships routine transport (or at least they used to do so) up
to 12 passengers. I regularly use my car for small-scale transport (up to
a few hundred kilograms 8-)). Some airline routes (e.g., Frankfurt-Rio-
Santiago) earn their keep through the mix of passengers and cargo they can
fly on the same plane.

Now, whether you want to combine the passenger car with the heavy-lift
truck - that is another matter, and is probably debatable. But the reason
why this is debatable has nothing to do with safety, as Barton and Gehman
seem to be suggesting.

I think it DOES impact safety - and the economics too.
Automobiles and airplanes are well-refined technology.
Even thus, a truck or plane designed for cargo is not
as well designed to safely transport people - and vice-
versa. Making something that does both jobs well is
difficult and more expensive than producing more dedicated
vehicles.