In article ,
Fred J. McCall wrote:
The original vision called for 40 launches a year (with 5 orbiters, I
believe), with an assumption of simple ground operation.

They had backed off to 24 with four orbiters by the time of the Challenger
accident. In practice, flying 9 flights in 1985 was a strain, and the
push to step up the rate further contributed heavily to the accident.

In actuality, they'd be hard pressed to manage 8 flights a year (with
4 orbiters).

If I recall correctly, the post-Challenger assessment was that there was
nothing about the 9/year rate that would have been fundamentally hard to
sustain... given greater investment in spare parts, support facilities,
and operations manpower, plus some simplifications like actually enforcing
the rules about not making late changes in payload manifests. The
orbiters weren't the "long pole in the tent" for flight rate, except
insofar as shortage of spares made it hard to keep them all operational
simultaneously.

Note that the post-Challenger flight rate was substantially higher than it
is today -- I think it was 8/year when everything went right. The later
reductions were for financial reasons, not because there is any deep
obstacle to the higher rate.

If (dim) memory serves, the fundamental limit set by having only four
orbiters was thought to be (in post-Challenger hindsight) something like
15-20/year. That rate would require quite a few more facilities -- e.g.,
two or three more of the big simulators at JSC -- and a lot of money. You
could probably go a bit higher if you first made substantial orbiter
changes, e.g. a nontoxic-propellants RCS/OMS system to remove the
bottlenecks in the orbiter processing that arise from having to clear the
area every time work even comes close to those systems.

Building up to even the maximum three-unmodified-orbiters rate *now* would
be extremely expensive, and would take several years even with unlimited
funding, because a lot of crucial items are long out of production, and it
takes time to build new facilities and train new staff.

Plus there is that little problem that at such rates, you're probably only
a few years from another loss-of-orbiter accident. (One of the more
interesting post-Challenger reports -- from OTA? I forget -- concluded
that ongoing orbiter production was mandatory for reliable long-term
operations, especially if projects like the space station needed a
guaranteed minimum fleet size. This was not what people wanted to hear
just then, so that report was quietly shelved...)
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