In article , wrote:

How many rockets exploded/failed in the 50s and 60s until they got it "right
?" (heck, Ariane has had a lot of recent explosions).

How many airplanes crashed until they got it "right"? The US has had what,
3 spacecraft accidents where life was lost?

There have been three accidents in the US involving the crew of a manned
spacecraft being killed whilst in the spacecraft; two in flight, one in
training.

There were two (three?) fatalities inside Columbia before STS-1 - two
technicians were caught in an area purged of oxygen - whcih you may or
may not feel falls inside your definition. There have also been
accidents in preparation of fuel, motors, &c; I don't have information
to hand, but they were in the 'manufacturing stages'.

What seems to be stopping NASA right now is the choice between a non EPA
approved foam that works and an EPA approved foam that doesn't work.

Except... this is a non-issue. The foam which didn't work, and didn't
work in a very spectacular manner last year, was the old "unhealthy"
foam...

CAB vol 1 pp51:

"BX-250, a polyurethane foam applied with CFC-11 chlorofluorocarbon, was
used on domes, ramps, and areas where the foam is applied by hand. The
foam types changed on External Tanks built after External Tank 93, which
was used on STS-107, but these changes are beyond the scope of this
section."
pp54:
"The Board has concluded that the physical cause of the breakup of
Columbia upon re-entry was the result of damage to the Orbiter.s Thermal
Protection System, which occurred when a large piece of BX-250 foam
insulation fell from the left (.Y) bipod assembly 81.7 seconds after
launch and struck the leading edge of the left wing."

Later, it discusses the effect of changing the foams:
pp129:
"The cause of the earlier-than-normal popcorning [on STS-87] (but not
the fundamental cause of popcorning) was traced back to a change in
foam-blowing agents that caused pressure buildups and stress
concentrations within the foam. In an effort to reduce its use of
chlorofluorocarbons (CFCs), NASA had switched from a CFC-11
(chlorofluorocarbon) blowing agent to an HCFC-141b blowing agent
beginning with External Tank-85, which was assigned to STS-84. (The
change in blowing agent affected only mechanically applied foam. Foam
that is hand sprayed, such as on the bipod ramp, is still applied using
CFC-11.)"

[In other words - the foam that was the root cause wasn't changed, and
the foam that was changed merely led the events to occur earlier rather
than start occuring. They were reduced to previously experienced levels
by STS-101]

I was sure there was a specific note about this somewhere, but a cursory
read-through hasn't found it.

[It's almost a pity it wasn't the EPA-induced changes that were the
cause - it could have made an excellent little parable about hubris]

--
-Andrew Gray