Hallerb wrote:
Fourth, among all the fatalities in space missions, there has been
exactly one flight (Columbia) where having a second spacecraft flying
the same mission profile might have avoided the casualties. Given

Well giving ISS a in orbit shuttle of its own could be very useful as a shuttle
support rescue vehicle, construction assistant, with enough propellants go
visit a near earth asteroid.

OK, so you're suggesting a craft with three dramatically different and
incompatible purposes. You want long on-station time (which the current
shuttle doesn't have) as a rescue vehicle. (And you would need two of
them, if you want one to go gallivanting off to an asteroid). You want a
small, nimble craft for a construction assistant. (I would envision
something which is not re-entry capable, has a small life support
section, and which downloads consumables from the station.) You want
something which is capable of a multi-month mission with considerable
delta-vee and radiation shielding on the order of Apollo. I suppose we
could fly up a shuttle and park it up on blocks in the back yard of the
ISS, but it wouldn't be capable of any of the missions you propose for
it.
This capability can save lives and increase excitement!
And to develop the capability would require a NASA budget about five
times what it is now...