Bill writes:

> a shuttle has a 1 in 200 chance every liftoff of having something
>  catastrophic happen - that's pretty lousy odds if you ask me...

The odds of catastrophic failure of a shuttle have been previously calculated
to be as low as one in every 75 missions. These odds were well known to NASA
before anyone flew on the shuttle, but the people who flew on it elected to
fly anyway. They knew perfectly well what they were doing, but felt what they
were doing was important enough to continue.


Tom writes:

> presuming the reported pressure was unexpected, and by that I also imply
>  "unexpectedly HIGH", we look to a probable cause: intense heat in the wheel
>  well, due [most likely] to missing tiles in the affected area -- tires are
>  basically baloons, and if they get hot, they expand like a hot-air baloon,
>  and may eventually pop -- the resulting "explosion" could destabilize the
>  craft to the point where the wings get over-stressed and tear off; and the
>  whole thing just "cascades" in failures...

A failure mode will be likely much more gentle than that. An interruption of
the hypersonic airflow pattern over the left wing due to the debris strike
pattern might, for instance, cause the control system to increasingly pitch
or yaw the spacecraft into an insustainable attitude, through a series of
oscillations of increasing amplitudes, sufficient to cause internal stresses
to break the frame apart at the seams.

People generally don't perform failure analyses on the HP3000 when it fails,
but all failures begin with a single, most "upstream" event that eventually
cascades into the complete loss of the system. The capacity to perform
backups obviates that work on a computer system. If good backups exists, the
system can be easily "brought back to life," if need be, on a completely
different set of hardware and never really notice the costs of the failure.
NASA, on the other hand, spends an inordinate amount of time working out
these fault trees, attempting to assess how severe a risk the failure of any
single component presents to the mission at any point in time.

Secondly, people have repeatedly mentioned how the crew was '"doomed from the
beginning" but didn't know it. That too is characteristic of all failures.
The seed of the failure always proves to be latent in the system, residing
there for perhaps months or years, not merely a few days. Shakespeare wrote
essentially the same when he had Hamlet say:

"So, oft it chances in particular men,
That for some vicious mole of nature in them,
As, in their birth--wherein they are not guilty,
Since nature cannot choose his origin--
By the o'ergrowth of some complexion,
Oft breaking down the pales and forts of reason,
Or by some habit that too much o'er-leavens
The form of plausive manners, that these men,
Carrying, I say, the stamp of one defect,
Being nature's livery, or fortune's star,--
Their virtues else--be they as pure as grace,
As infinite as man may undergo--
Shall in the general censure take corruption
From that particular fault."

Wirt Atmar

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