> I have some doubts. To quote a bit more from the letter I quoted in my last
> mail
>
> ""For non-reusable parts like the solid rocket booster and the external
> tank, each launch is a new statistical event for an item that has never
> flown or been test fired on the ground. Once a re-useable part works it will
> work every time if maintained to specification"

I agree with Olin- fatigue is a HUGE factor in reusable parts.  I think
a reusable part, even maintained to spec, is still more likely to fail
than a disposable part which is manufactured to spec.

QC can add a lot of nines to the reliability of a product, especially
when one factors in the money and effort NASA puts into it.  Say
an external tank is 99.999% reliable.  Each tank has that reliability,
per launch episode.

Launch the same 99.999% shuttle over and over, and fatigue will,
over time and in ways unpredicted by engineering studies, start
to reduce the number of nines in the equation.

Furthermore, the shuttle really can't be considered an efficient
reusable vehicle.  The effort involved in testing, replacing, and
bonding the heatshield tiles on the underside of the ship takes
similar effort to the building of a brand new Apollo-type craft.
After every mission.  AND the shuttles were speced for 100
flights or 10 years.  Columbia, at the time she was lost, was
22 years past her first flight.

Mike H.

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