Re: What was the biggest problem for each of the 2 destroyed US space shuttles?

From: Jay Windley (webmaster_at_clavius.org)
Date: 09/13/04 

Date: Mon, 13 Sep 2004 11:14:28 -0600

"Jay Windley" <webmaster@clavius.org> wrote in message
news:ci39kp$44q$1@news.xmission.com...
|
| | <Jay writes about learning by doing>
| |
| | Really? Have a cite for this?
|
| Yes, but not handy this evening.

I like your style of quotation markup, so I will adopt it.

<wynne>
"Beneath a public image of rule-following behavior and the associated belief
that accidents are due to deviation from those clear rules, experts are
operating with far greater levels of ambiguity, needing to make uncertain
judgments in less than clearly structured situations. The key point is that
their judgements are not normally of the kind -- how do we design, operate
and maintain the system according to 'the' rules? Practices do not follow
rules; rather, rules follow evolving practices." (Brian Wynne, "Unruly
technology: practical rules, impractical discourses, and public
understanding." _Social Studies of Science_ [18], p. 154)
</wynne>

I believe that rules for operating complex technology exist at two slightly
different scopes: one that derives from the design studies, and another
that departs from design studies and incorporates knowledge gained in the
field. They apply to different activities regarding the system's operation.
This is especially important for technologies such as the space shuttle that
are considerably innovative. While the written rules can govern at a broad
scope, the SRB field joint teams and their operators are better served by
information they obtain as a result of operating the joint and of testing it

<petroski>
"The very newness of an engineering creation makes the question of its
soundness problematical. What appears to work so well on paper may do so
only because the designer has not imagined that the structure will be
subjected to unanticipated traumas or because he has overlooked a detail
that is indeed the structure's weakest link." (Henry Petroski, _To Engineer
is Human: The Role of Failure in Successful Design_, p. 80)
</petroski>

This quote can also be interpreted to make a case for conservatism. That
is, if you can't know ahead of time how systems will behave, then you should
expect unanticipated failures. That seems paradoxical, I realize, but I'm
saying it seems to argue for staying well within the boundaries so that you
can use the resulting margin to address new failures.

More appropriately, I believe it addresses the notion that the rules have to
be looked at constantly for deficiencies in the design. You have
requirements and specifications, but those generally discuss what is to be
done and impose looser restrictions on how it is to be done. In order to
satisfy the requirements you impose operational rules that initially derive
from the design. But those rules are formulated -- especially in the case
of new technology -- from a tentative extrapolation of known basic
principles. As experience accumulates, satisfying the requirements entails
day-to-day operations that reflect what you learn.

Engineering decisions are made somewhere between perfect understanding and
total ignorance, so any system of rules to govern engineering decisions has
to be formulated to allow for variance as experience is accumulated.
Pretending that you can see the end from the beginning is not helpful.

Now having said that, the question that is more interesting to me is why the
decision-making process leading up to the eve of the launch seems to have
been broken.

In the first chapter of Charles Perrow's _Normal Accidents_ he discusses the
effects of slowly unfolding data upon operators. Accidents are always
investigated in hindsight, and the benefits of that hindsight are frequently
used to judge the operators in charge during the accident. A number of
psychological factors come into play: the value of interpretation, the
basic belief in safety and redundancy.

| | And I'll for a cite for this theory of yours that there is no
pre-existing
| | sense of right, wrong, safe, or broken for anomalies for the Shuttle.
|
| ...But I think you're going a bit farther with the statement than I
| perhaps intended, or perhaps I'm going too far. You still have the
| original requirements and expectations, and they still have value,
| but they are examined and perhaps modified as new information about
| safety and behavior becomes available.

I believe the quotations above support this view.

When you cannot fully predict the behavior of a system as it is designed --
such as in a complex space vehicle -- you have to write the rules that
govern its operation based on the information and expertise you have at
hand, however incomplete or speculative. Those rules can take the form, "Do
not operate the system in this certain way because this bad thing will
happen if you do." That's based on past experience with similar systems and
upon the general principles of design engineering.

But if, for whatever reason, the system is operated adversely and the Bad
Thing does not happen, then you might want to question that restriction. If
you go back and look at the consequences of your adverse operation and
realize that the system had a previously unforeseen margin or protective
interaction, then you can relax the operational rule based on new
information that the original designer did not have. Design ambiguity works
in both directions. 

-- 
                                          |
The universe is not required to conform   |  Jay Windley
to the expectations of the ignorant.      |  webmaster @ clavius.org

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